# Talk me into (or out of) a whole house heat pump to replace dead oil boiler



## NoGoodAtScreenNames (May 6, 2021)

Hi Everybody.

What I was optimistically hoping was a $500 service call from the oil tech ended up being a quote to replace our current boiler. I’ve had a heat pump in the back of my mind for a while but was hoping to get a few more years for the tech to mature and gain acceptance here instead of being a trailblazer as a primary heat source. 

Here’s my situation.

- 2800 sq ft house with 8’ ceilings in NE Mass. normal winter day is in the 20s and overnight dipping into the teens. There are usually a few days that we get close to 0 F as an overnight low.

- Current heating: 4  zones (upstairs, downstairs, single room partially finished in basement, mud room on first floor) baseboard heaters.

We use about 300 gallons per year with burning 2-3 cords. I would want to size the new system as if we were not wood burners though.

- Insulation: house is fairly tight, no noticeable drafts. R-49 in walk up attic, R-19 in the walls plus exterior foam board under the siding. Basement is partially finished, walls are mostly insulated.

- Air Conditioning: House is ducted for single zone AC. There are booster fans that can be turned on for upstairs but I haven’t seen them make a noticeable difference. 

Indoor unit is 10 years old. Outside is at least 25 years old and has got to be nearing its end.

- Electricity: We pay $0.16 per kWh when pulling from the grid. We get paid $0.04 per kWh we send back. This is measured in 15 minute increments. So basically no offsetting production. It is 4x better for me to use my solar immediately than to send it to the grid to offset night time / cloudy days. I figure a heat pump is a good way to use my excess solar during the day especially in the shoulder seasons. 

Everything else in the house is electric - heat pump water heater, induction stove etc. We currently have 100 amp service. Expanding to 200 amps is not an option. We looked at it while installing our solar system and it would be $8k since it’s an underground line and crosses under 4 neighbors driveways. However 100 amps seems to be treating us fine now. I can’t imagine the heat pump using more electric than the old AC on a hot August day - unless it kicks into resistance mode heating. 

Install costs: Replacing the boiler will be $10k. I haven’t talked to anyone yet about a heat pump. There is a rebate of $1,000 per ton for new heat pumps. I assume I would need at least a 4 or 5 ton unit based on house size. 

Ducted or Ductless: I do not want a mini-split system with big units hanging on the wall (except for the partially finished basement or mud room). I was hoping either to use a zoned air handler or I could install in the ductless units in the basement and push air through the 1st floor floor registers. For upstairs maybe using an air handler for a single zone. Not sure if this is possible but maybe using short run air ducts up from the basement or running the lines through the old ducts to an in floor register. I’ve seen some concealed units or some floor mounting options that could look ok. But again, big ugly thing hanging high on the wall isn’t going to get approved.

Any thoughts or things I should be asking the heat pump guys?

Thanks!


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## EbS-P (May 6, 2021)

To make sure I’m understanding you you have ducting for the first and second floors with an interior air handler?   Ducting to the basement?   If you have ducting for AC I would definitely explore an air to air heatpump.  Around here multiple zones get multiple compressor units and air handlers usually done by floor.  

i hear you about being first adopter of new technology but air to air heat pump are not that. Getting one that can do more than 50% of rated capacity at cold temps say (single degrees). That’s the newer. Variable speed compressor for large systems that’s newer too. Air to water heat pump that emerging tech here in the states.

get some ideas of what’s available by calling around and check them out at this website.
https://ashp.neep.org/#!/


I think it sounds like a good idea especially with the incentives. Those I think aren’t likely to increase in your region soon.
Evan


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## NoGoodAtScreenNames (May 6, 2021)

Thanks Evan.

Yes we have a single air handler for air conditioning on the first and second floors. I can turn on some inline booster fans that go upstairs but its all one zone run off one thermostat.

No duct registers in the basement though it would be easy to add whatever we need down there in the "finished" room. At worst the basement is just drop ceilings and we have access to all the 1st floor joists. I could probably live with an air handlers for the first and second floor assuming they were zoned separately and a mini-split for the basement room and mudroom.

I guess my main concern is that the heat pump talk tends to be really focused on zoned mini-splits and the efficiency gained by avoiding duct losses. But that gets people like me that would be perfectly happy with an air handler ducted system from trusting heat pumps to keep up with a cold New England day. In reality, I'm not worried because the wood burning takes care of that now, but again, I don't want to have to rely on wood to be comfortable (65F to 70F) when its 10F outside.

EDIT:

The current air handler for the AC is in the basement / inside the building envelope. I know duct losses can be extreme when they are placed in an attic out of the envelope / on top of the insulation. Luckily, that wouldn't be the case here.


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## EbS-P (May 6, 2021)

NoGoodAtScreenNames said:


> Thanks Evan.
> 
> Yes we have a single air handler for air conditioning on the first and second floors. I can turn on some inline booster fans that go upstairs but its all one zone run off one thermostat.
> 
> ...



Seems like you are really almost the perfect candidate to got air to air heatpump.  They are now selling variable speed compressor units like you would need.
Easy install makes for less cost and why the mini splits are popular.
I think this one is really oversized but just look at the general specs.  https://ashp.neep.org/#!/product/27356

these are the important cold climate numbers.


Capacity Maintenance (Max 5°F/Rated 47°F)76%
That’s quite good from what I have seen


We have a basement on the single zone heatpump. It’s not ideal. I’ve thought about adding a mini split. But really 5000$ for a Mitsubishi 1.25 ton units just doesn’t make sense. Right now. It get cold when we run the stove upstairs but if I close off all the vents upstairs and up them all downstairs (I added two more this winter). We got by just fine. A space heater or two will work for the coldest week of the year.
I after 3 years of 90% wood heat I’m going to run the heatpump more. Say 60-75% of the heating load for the next year and see how the basement gets along.   Ideally I want to put the 4K not towards a mini split but a really efficient 4 ton unit and new ducting.
Evan


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## begreen (May 7, 2021)

We've had a central heat pump system for the past 15 yrs. It mainly carries the load during mild shoulder season weather and it replaced a propane forced air furnace that cost a fortune to run.  We heat with wood when temps drop below 45 usually. The HP is an American Std. Heritage 16 with a 2 stage compressor. It is tied into an AS variable-speed air handler. There are resistance coils in the plenum that have been used just a few times when we are away. All the ductwork is insulated, supplies and return. The only cost has been replacing the filters. The current options for even higher efficiencies in package units were not available at the time. When/if it has to be replaced it will be with a high-efficiency, central combo from Daikin, Mitsubishi, or maybe Mr. Cool?


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## woodgeek (May 7, 2021)

"I’ve had a heat pump in the back of my mind for a while but was hoping to get a few more years for the tech to mature and gain acceptance here instead of being a trailblazer as a primary heat source."

I guess I was a weirdo for ripping out an oil boiler in 2010 then, and switching the whole house to a single speed, single zone 4 ton central heat pump!

I think you can do it if you want, the biggest issue IMO is the 100 A service.  My house burned 600 gals at its current insulation level, and needs 12 kW to keep up at 0°F.  So you would probably be Ok with a 8 kW strip, minimum, or 32A.  Any installer you find will want to put in 12 or 15 kW, and it will be a no go on the box.

The other issue is that the ducting on your AC is probably too small.  

If I were you I'd get a variable speed compressor, ducted system, 3 tons would probably be good.  You will need the variable speed to get summertime dehumidification.

LOTS of design options.

Do you need four zones...that makes it hard.  Can you do 2, like up/down?


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## NoGoodAtScreenNames (May 7, 2021)

The 4 zones is how the oil is - not how it needs to be in the future. Mudroom could be easily brought into the 1st floor zone and the basement zone is really a single room maybe 12 x 16. We don’t actively heat either one and neither would need AC. Basement stays around 58 in the winter with the heat pump water heater stealing waste from the boiler with the thermostat set at 50 so the heat never really comes on.

We did upgrade our circuit box when doing the solar so there is some physical space but it’s still 100 amps feed and it’s a big house to be running on 100 as is. This is the piece that worries me though. I assume some installers will say let the oil take over when it gets cold. But if I pay for a new boiler I don’t have a budget for a shoulder season heat pump. I would just increase my min temp to start a fire. But my AC is due to kick it pretty soon so combining them seems to make the most sense if my electric capacity can support it.

I have some feelers out so we’ll see what they say.


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## Highbeam (May 8, 2021)

There are heat pumps with propane for back up instead of electric resistance heat. Wouldn’t need much amperage for that.


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## EbS-P (May 8, 2021)

NoGoodAtScreenNames said:


> The 4 zones is how the oil is - not how it needs to be in the future. Mudroom could be easily brought into the 1st floor zone and the basement zone is really a single room maybe 12 x 16. We don’t actively heat either one and neither would need AC. Basement stays around 58 in the winter with the heat pump water heater stealing waste from the boiler with the thermostat set at 50 so the heat never really comes on.
> 
> We did upgrade our circuit box when doing the solar so there is some physical space but it’s still 100 amps feed and it’s a big house to be running on 100 as is. This is the piece that worries me though. I assume some installers will say let the oil take over when it gets cold. But if I pay for a new boiler I don’t have a budget for a shoulder season heat pump. I would just increase my min temp to start a fire. But my AC is due to kick it pretty soon so combining them seems to make the most sense if my electric capacity can support it.
> 
> I have some feelers out so we’ll see what they say.


My unit Trane 16, the heat strips kick on when the unit goes into defrost mode (ie. A/C mode). Other wise it will blow AC cooled air.  We lived two or three years without working heat strips as they were probably defective when the unit was installed and I had no clue.  It was fine until it got cold. Here that’s 30 degrees.   Or probably woodstove temp for you.  So it’s a code issue. Not an operational issue.  New heatpump installs here must be permitted and inspected.  Question might be do you HAVE to install heat strips?


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## peakbagger (May 8, 2021)

A VRF system based on an outdoor air to refrigerant cold climate heat pump is probably the optimum system. They are rapidly becoming the go to solution for multi zone systems. Unlike multihead minisplits, they can heat and cool simultaneously. The system monitors the demand and flips from primary heating to primary cooling and if one or two zones needs heat while the other two are cooling, the system can use the heat removed from cooling to partially heat the other spaces. if the overall demand changes the outdoor unit flips to whatesver demand is dominant. The options for terminal units are wider. Sure you can get wall mounted air handler but you can also get duct mounted unit. The refrigerant lines due need to be run to the terminal units but compared to ducts they are much smaller.

This combination is getting quite popular for new high end homes and commercial systems the problem is the cost to retrofit is steep.


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## NoGoodAtScreenNames (May 8, 2021)

Heat strips are just to defrost the outdoor unit right? I assume those would run at a lower amperage than a resistance heat coil trying to heat the house directly.

I’ll have to find out what the code, if there is any here, on the minimum temperature needed for the primary heating system. If I had a system that was still in heat pump mode at 0F. I could probably be ok with lower   Amp demand for back upheat coils. But if code says I need a certain amperage heat coil to go down to -10F then I may be out of luck with 100 amp service.  The current boiler runs on a 240V 50 amp breaker. I assume if a heat pump at maximum usage could stay under that I’d be ok code wise with what I have. We’ll see...


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## maple1 (May 8, 2021)

That sounds like a really crazy price for an oil boiler swap? My first thought is do the central heat pump AND replace the boiler. Be a shame to abandon that hydronic system. I like redundancy, and you might find (I would bet will find) you aren't quite as comfortably warm as you want to be on your colder days. But holy crap, that's big $. Around here there have been really good buys on fairly newish boilers that people are swapping out for other heat sources.


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## woodgeek (May 8, 2021)

MORE:

1. The heat strips will run two ways....when the defrost cycle runs AND when the HP can't keep up (on your coldest single digit days).  For the first case, you don't actually need it...the heat to melt the ice comes from chilling conditioned air in the home.  The heat strips are downstream of the coils, and the system just warms the air so that the homeowner doesn't get a blast of cold air out the registers for a couple minutes every hour or two (they hate that).  

If you try to size the HP big enough for your coldest design temp, it will be way oversized for normal conditions (and more expensive), so that is why they go for a properly sized system (that can just cover your heat need at typical January/Feb temps).

2. In my case, I installed the HP and left the old boiler, and used the boiler as a backup, specifically as a 'second stage' on the thermostat.  This didn't make the HP a 'shoulder season heater', although some installers will assume that is the case.  The HP covered 80+% of seasonal demand, with the boiler kicking on only on coldest days in Jan/Feb.  So, I realize your boiler is dying/dead.  IF, however, you can patch it up to working condition, you could use it for backup.

3. I upgraded my service from 100A to 200A, whole new box, etc.  And then the installer didn't change the aerial line from the street!  I assumed that that would need to be upsized.  He said 'nope!' they're all the same size around here.  While your line is buried, you might check with a pro to see exactly what the ampacity limit on the wire is, you might get lucky.  If it was 150A, you can add a second 50A subpanel for the HP.  And again, I think bc of your insulation level, you only need 8kW (32A) for your backup.

4. I also assumed that when I had a 100A breaker box, if I added up all the breakers, they would have to be less than 100A.  And 200A for the 200A box.  But that does not seem to be a code requirement.  I'm not a pro, and you will need advice from a pro....but if you are adding up loads and breaker sizes from your appliances and coming in a little over 100, that may not be a problem. The code (I think) assumes that not all the loads are running flat out at the same time....there is a slight derating that occurs.  I think when I was running my strips, and my HP and charging my electric car, and my HPWH and my oven all at the same winter day, that was only 24 kW, or 100A.  On my 200 A box.

Bottom line: If you want a central HP, I think you are a GREAT candidate for a central system, primarily bc of your high insulation level.  Since a 3 ton would cover you (on typical Jan/Feb) days, you COULD upsize to a 4 ton to further reduce backup needs (bc a 3 and 4 ton unit price is very similar, you are gonna get hit on install cost and wires and ducts).  I'd quote a 3 and a 4.  As for the strip backup, either you can put it on your box, or not, according to code.  If you can, then not a problem.  The middle case is where the HVAC guy wants 15 kW strips, bc he oversizes them all to avoid callbacks, but the electrician says you can't have more than 8 kW.  In that case you need to do a load calc on your house to confirm 8kW (x3414 = 27,312 BTU/h) is sufficient for your min temp (like -10°F).  Etc.  Keep in mind that a smaller strip is more efficient (bc it runs on defrost for comfort, you are making expensive BTUs even during mild weather) but that the smaller strip will only mitigate the cold blasts...in defrost the unit will push >50 kBTU/hr outside, the 8 kW strip might only get the air up to cool, from cold.

As for tech, IMO minisplit or central doesn't matter...what matters is **variable speed compressor**.  In New England the heat BTUs are way higher than AC BTUs, and an oversized AC doesn't dehumidify.  The variable speed compressor will allow it to throttle way down in AC mode, to get proper dehumidification.  My system struggles with humidity in the summer...I have other mitigation strategies for that, but when the compressor dies, the next one will be variable speed.

If you are 'nervous' about the HP being sufficient, patch up the boiler and keep it another season or two for backup security.  That is what I did.

In the end...I am using a low-tech, single speed HP, and my climate is only 4°F warmer than yours in every month of the calendar.  My system is low maintenance and comfortable.  The whole 'oil heat is best' and 'hydronic is the best', I don't agree.  The oil boiler was loud, smelly, gave us low grade CO poisoning for a month once, and having hot radiators behind all my furniture was a PITA for decorating.  The forced air blower is near HEPA filtering all the air in my house 12 mos a year, for less dust and allergies. No regrets at all.

Get some quotes!  And disregard what many old installers tell you... mine told me 100 reasons why my system would never work.  Crazy.


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## EbS-P (May 8, 2021)

NoGoodAtScreenNames said:


> Heat strips are just to defrost the outdoor unit right? I assume those would run at a lower amperage than a resistance heat coil trying to heat the house directly.


Heat strips are only for the circulated air. Most compressors have their own heater (less than 200W) to make sure they operate at low temps.  Neither of them defrost the coils.


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## stoveliker (May 8, 2021)

As some said above, in my previous home I had put in a new heat pump with gas "emergency heat" (rather than the standard heating coils that indeed heated the home when it was below 40 F there, indeed in the South). I really liked that because when it was cold outside the air blowing into my home was really warm. Also when the thermostat was set far above the current temp in the home, the gas kicked in, and it heated the home really quick. So we slept cold and in the morning it was warm in 5-10 minutes of hot air blowing.

If you have natural gas, put in a heat pump and gas back up. Not sure that is financially a good idea when you have to buy propane ..


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## semipro (May 8, 2021)

@NoGoodAtScreenNames I'd suggest you check out the HP below to get an idea of some of the newest tech out there.  We're using one now and have another on order.  They have their strong and weak points but they are pretty innovative.  A couple of key aspects:

Can be configured as either a 2 or 3  ton system.
Heats at very low ambient outdoor temps (in our case, no backup electric heat strip needed.  We have wood stoves anyway)
Very quiet outdoor unit, compact, can be wall-mounted.
Variable-speed inverter compressor
Air handler fan not variable speed (I wish it was) It is a multispeed DC motor but the speed is not modulated according to conditions.
Outside unit defrosts by running briefly in cooling mode (which does blow some cold air out inside registers)
I'm not necessarily recommending this system for your application but it's working great for us.









						MRCOOL Universal Series DC Inverter Split System  |  MRCOOL
					

Advanced DC Inverter Technology. The MRCOOL Universal Series -  Up to 20 SEER Central Heat & Air Systems




					mrcool.com


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## begreen (May 8, 2021)

semipro said:


> Air handler fan not variable speed (I wish it was) It is a multispeed DC motor but the speed is not modulated according to conditions.
> Outside unit defrosts by running briefly in cooling mode (which does blow some cold air out inside registers)


I am sorry to hear this. I was considering this unit. We love the quiet operation during shoulder season. With the compressor on low speed and the air handler also running at low speed the system is almost silent.


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## velvetfoot (May 8, 2021)

10 grand seems like a lot to me too for just replacement.  

Not sure why the oil boiler is on a 240v. 50amp breaker, unless it's shared or something.  One of the advantages of an oil boiler is that it just needs a small genny to run during a power outage, with those little circulators, keeping you toasty, and likely in hot water.  In NE Mass, you're not gonna die in the summer w/o a/c, but maybe without heat in winter.

Baseboard hot water heat is a quiet and even heat.  You might not like the results with an air system; how much additional ductwork and modifications, even with existing a/c?

Of course, fossil fuels can always be legislated away, or maybe re-jiggered for the 'proper' price signals.  Also, around here, I got a brochure from the electric utility saying, I thing, that they'd help financially with the conversion to electric.

If you're looking to burn more kWh, how about a plug in hybrid, or a hot tub?


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## maple1 (May 9, 2021)

Yes that 240v 50amps sounds very odd. Mine was on a 120v 20a.


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## NoGoodAtScreenNames (May 9, 2021)

So I was mistaken about the current breaker. I’ve never had to turn it off at the main so just assumed based on the bad labeling. Looks like it’s running on a normal 20 amp unlabeled breaker in the box. The 50 amp was labeled “HVAC” and another 15 amp double pole was labeled “AC”.  After switching some things on and off the 15 amp is the air handler.  So the only thing left for the 50 amp would the outside AC unit. I’ll try narrowing that down when it’s a little warmer and can try running it. Either way, whatever it feeds would be taken over by the heat pump. What size breakers do primary heat pump systems normally run on?


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## maple1 (May 9, 2021)

Sounds like there are still a lot of unknowns re. heat pump application to your situation. Mainly around existing ducting and zoning but also around possible heat strips and their use - thinking the100 amp service will severely limit you for that.  And I dont think I would want heat strips anyway but that could just be a personal aversion. Ducting requirements could vary quite a bit going from light a/c use, to full time whole house heating needs. So I'd encourage getting a heat pump/HVAC guy in (more than one actually) for an assessment and recommendations. I think I would also get a second opinion on a new oil boiler - there are still quite a few decent looking used ones here, after checking the local used classifieds a bit ago. (Altho even after saying that I can understand wanting to get rid of oil and oil tank - just wouldn't want to give up that hydronic system).


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## semipro (May 9, 2021)

NoGoodAtScreenNames said:


> So I was mistaken about the current breaker. I’ve never had to turn it off at the main so just assumed based on the bad labeling. Looks like it’s running on a normal 20 amp unlabeled breaker in the box. The 50 amp was labeled “HVAC” and another 15 amp double pole was labeled “AC”.  After switching some things on and off the 15 amp is the air handler.  So the only thing left for the 50 amp would the outside AC unit. I’ll try narrowing that down when it’s a little warmer and can try running it. Either way, whatever it feeds would be taken over by the heat pump. What size breakers do primary heat pump systems normally run on?


The HP I reference above uses 24 amps for the outdoor unit and about 10 for the air handler.


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## EbS-P (May 9, 2021)

I don’t like how most of the marketing of efficiency is geared towards cooling.  Here in southeastern NC, (the south mind you on the coast)we have more cooling degree days than heating degree days. Not by much mind you but peak inside versus outside temps summer would never be more than 25 degrees but winter can be as much 55 or 60 if it’s record setting cold.  
Don’t even get me started on trying to find someone to do an actual load calculation.  

Given your location and fact you utilize wood heat, finding that balance between cost and efficiency is something to think about. A 14 SEER unit with heating rating of 8 might make more sense than a top of the line 20 SEER unit. But my general rule is buy the most efficient HVAC system you can afford. My only recommendation is that the variable speed blowers are nice. Took me 9 years to finally figure out that the thermostat wire did not have enough conductors (need 7 in total. 2 stages for heat and cooling plus emergency heat (the strips), fan and ground) to allow for fan control and to flip the dip switches and put mine Trane blower in enhanced mode. And I only found out about it by reading the manual.

my 3 ton with air handler is on a 40A and heat strips are on a 60A.


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## NoGoodAtScreenNames (May 9, 2021)

Thanks everyone. At this point I may be leaning towards replacing the oil burner with as cheap and efficient one as I can get. Natural gas isn’t an option on my street. The quote is for. Buderus G155-4 with a Riello burner and new zone valves, pump etc. 

As I mentioned in the original post, the air conditioner is probably on its last legs as well. Maybe it makes sense to do a heat pump primarily as a replacement for the ac. I can get one that does well in cool to cold weather and still have the oil to take on the really cold days. The coldest time of the year for us is the shoulder season when it’s too warm for a fire and we’ve already turned the boiler off for the season. Running a heat pump on a rainy 52F day would be nice. I’d still want the heat pump to perform well in cold weather, but without resistance heat as a backup I could probably make due with the 100 amp service.


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## clancey (May 9, 2021)

Don't they have a heat pump that does AC and Heat as well----don't really know what exactly a heat pump is as well as don;t really know what shoulder season is?...clancey


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## NoGoodAtScreenNames (May 9, 2021)

Heat pumps are basically air conditioners that can run in reverse so they pull heat from outside and put it in the house. Most of them now will be dual use for heating or cooling depending on the season. 

Shoulder season is the Fall / Spring when the heating need is lightest. I don’t know why it’s called shoulder season... I hadn’t heard the term before hanging around here.


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## clancey (May 9, 2021)

Thanks and taking a guess here about shoulder season now I would think that if the heating season fall and spring is the lightest then it is time to go out and chop wood for the next winter to replace whats been burn"t...Just a guess---one needs to use their shoulders to chop wood and maybe that's how the name came to be but at least now I know when it is fall and spring...clancey


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## semipro (May 10, 2021)

begreen said:


> I am sorry to hear this. I was considering this unit. We love the quiet operation during shoulder season. With the compressor on low speed and the air handler also running at low speed the system is almost silent.


Although the air handler fan speed does not vary in operation, it does decrease by about 1/3 when you switch configurations from 3 to 2 tons.  This is done using DIP switches on the control board of both indoor and outdoor units.


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## Highbeam (May 12, 2021)

semipro said:


> Although the air handler fan speed does not vary in operation, it does decrease by about 1/3 when you switch configurations from 3 to 2 tons.  This is done using DIP switches on the control board of both indoor and outdoor units.



Seems you would always want a certain flow rate to always deliver heat/cold to each register sufficiently.


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## begreen (May 12, 2021)

Highbeam said:


> Seems you would always want a certain flow rate to always deliver heat/cold to each register sufficiently.


The higher flow rate is not necessary when the indoor temp is near stasis. In shoulder season weather above 50º our heat pump and air handler are usually running at half speed. This is also true of several high-efficiency furnaces.


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## Highbeam (May 13, 2021)

begreen said:


> The higher flow rate is not necessary when the indoor temp is near stasis. In shoulder season weather above 50º our heat pump and air handler are usually running at half speed. This is also true of several high-efficiency furnaces.



So those rooms with high demand at the end of the duct run just don’t need conditioning? Do you think this depends heavily on duct design, return location, house shape?


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## semipro (May 13, 2021)

There seem to be several HVAC modes where multiple/variable speed air handler fans would be an advantage and various methods for accomplishing that.  Here's some related info that I've gathered (though I'm sure this is not all totally accurate.  

Single (really set) speed AC PSC motor -  These usually have multispeed capability depending upon how they're wired.  The speed (RPM)  changes in operation as the duct conditions change.  A restricted air filter will actually cause the motor speed to increase and the flow to decrease because the blower wheel is a centrifugal device. (not intuitive I know).
Variable speed AC motors - the blower speed varies depending upon conditions like the temp differential across the coil or setpoint versus outside temp, etc.  These typically require a variable frequency drive unit (VFD). 
Multi-stage systems - both the outdoor compressor/fan and the indoor air handler together run at different preset speeds depending upon the stage.  This is what @begreen  described above (I think). 
Variable speed DC motors, or electrically commutated motors (ECM) - These may be more efficient overall than AC PSC motors.  These are "smart" in that they can change speeds to maintain motor torque, airflow, or motor speed.  Although they can operate at different speeds depending upon the signal/power they get, many are set to operate at a constant speed.  The advantage of this is that these motors can compensate for changes in the system like a dirty filter.  For example, they can increase speed to maintain flow over the coil to prevent freezing up if a filter is dirty or some registers are closed.  
True, variable speed in operation air handler motors, whether AC or DC - vary in speed in synchronization with the outside unit, usually an inverter compressor type unit.   Rather than operating in single or multiple stages of heating/cooling, they vary infinitely (or with many incremental "stages") to provide operation over a wider range of conditions.   I suspect that many mini-splits operate in this manner.  It requires special communication between the indoor and outdoor units that is not present with standard thermostat wiring. 
In general, decreasing the AH fan speed is useful because it can reduce fan power requirements, reduce evaporative cooling during heating, and reduce fan noise, energy use, etc.

My challenge, and the reason I've been researching these issues, is that I'd hoped that a smarter system might allow me to shut off registers to bedrooms at our house where we don't want heat while maintaining warmth in bathrooms.  There are various systems comprised of electrically controlled duct dampers,  remotely controlled electrical registers, and even inflatable airbags within ducts to strategically control flow to individual rooms.  However, these systems do not typically coordinate with AH fans, and unintended consequences such as coil freeze-up, increased register airspeeds and evaporative cooling, and increased AH fan energy use may result.


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## begreen (May 13, 2021)

Highbeam said:


> So those rooms with high demand at the end of the duct run just don’t need conditioning? Do you think this depends heavily on duct design, return location, house shape?


Yes, proper system and duct design are important  Our system is balanced with the longest takeoff runs being under 15 ft from the supply trunk ducting.


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## EbS-P (May 14, 2021)

begreen said:


> Yes, proper system and duct design are important  Our system is balanced with the longest takeoff runs being under 15 ft from the supply trunk ducting.


After removing some of the insulation and ducts I found that every takeoff run was started from the trunk with a manual balancing damper.  Restricting the short runs should increase flow a bit in the longer runs.    Interesting concept if done correctly.   More interesting idea would be to use some type of actuator on these dampers to control each room / run. 
Evan


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## begreen (May 14, 2021)

EbS-P said:


> After removing some of the insulation and ducts I found that every takeoff run was started from the trunk with a manual balancing damper.  Restricting the short runs should increase flow a bit in the longer runs.    Interesting concept if done correctly.   More interesting idea would be to use some type of actuator on these dampers to control each room / run.
> Evan


Exactly, our system has dampers on the shorter runs. It took about 30 minutes to fine-tune the system once it was up and running. Sealing connections to reduce leakage is also important.


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## NoGoodAtScreenNames (May 19, 2021)

I talked to the first guy before he comes out to do an estimate. He recommended trying to fix the boiler. It’s leaking from the face plate of the tankless coil (that we don’t use anymore since we have a HPWH). The prior owners installed a seasonal hot water system - oil in winter and electric in the summer. If he can fix the leaking, he advised keeping the boiler officially on during the summer, but adjust the temp down so it only cycles once or twice a day. This would protect it from leaking in the future. While I don’t love burning oil in the summer it will should be a very small amount.

For the heat pump / AC, he recommended two separate air handlers for the first and second floors. One would be in the basement and the other in the walk up attic. I know air ducts in attics are frowned upon generally. The attic is open an spacious - a lot of people in the neighborhood with the same house design have converted them into living spaces. It will be convenient to access if needed. The insulation now is fiberglass batts between the main joists and then a second layer of R-30 layer perpendicular on top with a raised platform walkway going down the middle with exposed insulation near the eaves. The ducts could be under enough insulation that they would essentially be in the building envelope. As it is the attic stays fairly cool in the summer for an attic about 100F on a typical summer day.  We have a radiant barrier and solar panels on the south side providing shade.  In winter it’s fairly cold up there but warmer than outside and when it’s really cold we probably aren’t running the heat pump with wood with the oil back up. Still, I’m sure that there will be some replies to not put an air handler in an attic. Talk me into (or out of that) I guess as well. 

We have someone else coming on site on Friday so we’ll see what they think.


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## EbS-P (May 19, 2021)

How many rooms / vents would there be on the second floor?   Would the second floor get its own zone then?  All the suggestions seems reasonable. 

If you don’t keep the boiler running it is just going to keep degrading.   Couple thoughts I had.  The heat pump without resistive strips while not the most comfortable solution by itself should be able heat the house enough to keep the house livable on its own even when temps really drop outside. I’m guessing when in the single digits your heat pump could pump out 20k btus.  I bet it could keep Temps above 50 degrees inside but I’m just guessing.  No frozen pipes while you are way. So I could make an argument to do away with the oil burner but if it can be repaired I do think that’s the best plan.  

Attic ducts while undesirable aren’t terrible.  Insulate well and you’ll be fine.  

I kept trying to think of what you could do with 100 amp service if you didn’t have a wood stove and wanted to ditch the oil heat. I kept thinking a complete boiler replacement is in the same ballpark as an electrical service upgrade.  New boiler  will need annual maintenance and have a 20-30 year life while the upgraded service would probably be fine for the rest of your life.  

just some thoughts.
Evan


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## NoGoodAtScreenNames (May 19, 2021)

EbS-P said:


> How many rooms / vents would there be on the second floor?   Would the second floor get its own zone then?  All the suggestions seems reasonable.
> 
> If you don’t keep the boiler running it is just going to keep degrading.   Couple thoughts I had.  The heat pump without resistive strips while not the most comfortable solution by itself should be able heat the house enough to keep the house livable on its own even when temps really drop outside. I’m guessing when in the single digits your heat pump could pump out 20k btus.  I bet it could keep Temps above 50 degrees inside but I’m just guessing.  No frozen pipes while you are way. So I could make an argument to do away with the oil burner but if it can be repaired I do think that’s the best plan.
> 
> ...


Not sure about vent placement but the second floor would be a single zone. Upstairs is probably around 1,200 sq ft - 4  bedrooms, 3 baths plus a small office. So a lot of wall divisions - especially since my daughters door only opens twice a day...

I thought about the cost of a new boiler vs the cost of upgraded service as well. I would want something that was able to maintain at least 65F without a fire going. That could be because the boiler kicks in or resistance heat is used. In reality I’ll be burning wood so the house will be comfortable regardless.

For resistive heat with 100 amps is it possible to upsize that later or over do it now but set it so it doesn’t ramp up too much? So could I get something that could run up to 40 amps but keep it from ever using more than 20 until the service is upgraded? If not could I add resistive heat to a system down the road without a complete replacement? I still keep thinking though that my outdoor condenser is on a 50 amp breaker and the air handler is on a separate 15 or 20 amp breaker. How much resistive heat could I get with switching those over to a heat pump?

That all being said a service upgrade is probably somewhere in my future but the budget would like to find another way around that if possible. Doing solar, a kitchen remodel and this all within a year is eating into the kids college fund...


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## Highbeam (May 20, 2021)

The resistive strips are super cheap, simple, small and upgradable. You could buy a low wattage set and a high wattage set now to be swapped in later just to sure the bolt holes all match up. Be sure the wiring being run allows for the amperage draw of the higher wattage strip heater. We call them strip heaters but it’s more like a few coils.


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## EbS-P (May 20, 2021)

NoGoodAtScreenNames said:


> If not could I add resistive heat to a system down the road without a complete replacement? I still keep thinking though that my outdoor condenser is on a 50 amp breaker and the air handler is on a separate 15 or 20 amp breaker. How much resistive heat could I get with switching those over to a heat pump?



I’m guessing that on most air handlers thave a spot to install the strips and can accommodate strips with different power levels. So it seems plausible that you could install /upgrade at a later date. Would the installer want to do it that way? I’m not sure how low the the strips go but my 10Kw strip is on a 60A so you could get 3 kw on a 20 easy if they make them. I would have them install and pull wires from the recommended  strips now but leave them out of the main panel for now.  I think having everything their now but not being used would be a simpler install down the road. Slide in strips, pull wire into panel and connect to appropriate sized breaker.  20 minute job. 

I’m guessing that a 4 ton unit will be on a 40 maybe 50 amp. Still need the air handlers on a separate breaker if air handler is separate from the compressor (again guessing).

I’m right with you in the upgrades.  New roof big renovation upstairs, Diy renovation on 1000 sq ft basement that just won’t end.  My record is 5 trips in a single to “get more done store” but sure doesn’t feel like it.


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## woodgeek (May 21, 2021)

OP: "We use about 300 gallons per year with burning 2-3 cords. I would want to size the new system as if we were not wood burners though."

The KEY factor in all this is your winter BTU demand, both for sizing the HP compressor tonnage AND figuring out how big strips you need (and thus if your panel can carry it).  And this info from the OP is key.

Let's say a normal winter is 2.5 cords and 300 gallons total per year.  If we figure each cord displaced 150 gallons of oil, then this is 150*2.5 = 375 + 300 = 675 gallons of oil/yr if OP never burned a twig.  If this figure includes the boiler is running all summer and it has a standby oil consumption of at least 0.75 gal/day, or 100 gal during the non heating season, we would discount this.  But it sounds like the OP shuts it down, so I'll run with the 675 gal/yr figure for heating.  Summer shutdown also gives a higher seasonal eff rating (no parasitics).

675 gal * 138,000 BTUs/gal * 0.75 (true eff) = 70 MMBTU/year. DEMAND

If we assume that OP has an annual HDD of 6000, then we can figure:  70 MM/ 6000 = 11,600 BTU/HDD.  This is ~500 BTU/hr°F for his house envelope.

In MA, I would design strip heat to carry a -10°F temp with no heat pump, to 70°F, which is +80°F dT.  Given that loads are slightly quadratic (due to stack driven losses going like dT^2, while conduction losses are linear) I'd round up to 90 or 100°F dT.  This implies that heating with strips during a polar vortex event would be 45-50,000 BTU/hr.  Since strips are 100% efficient, this is 13-14.5 kW of strip heat.  14.4 kW of strip heat pull 60A at 240V.

So, if he rips out the boiler, OP needs *15 kW strips*, wired with 75A wiring and breaker (80% service rating).

CHECK: I have an older, 2340 sq ft house with a HP, it would call ~500 gallons per year, and I have 15 kW strips.  I have estimated that my demand at 0°F is about 12 kW, based on timing the thermostat duty cycle.  So 15 kW is sensible.

OP question: the strips themselves are just small coils like in a toaster that live in the air handler, and cost like $200, and are easy to swap out.  The cost is in the heavy wiring run to the air handler.  You are looking at 75A wiring and breaker.  IF you decided to install undersize strips (while the boiler remains as a second stage), you would still install 75A wiring, but say put in a smaller coil and breaker to match.  At a later date (when your service is increased, say), the coil and breaker can get swapped out to 15 kW for a few hundred dollars of parts.









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The other decision is tonnage.  If you get two units/zones, total tonnage.  I'm on a 4 ton system, and based upon OPs colder climate and 15-20% higher estimated demand, he needs 5 tons minimum, which is the max size for a single compressor unit.  My system carries me to about 24°F outdoor temp.  I run the HP down to 5°F, and the second stage makes up the difference.

The issue to come up is the installers.  They are all gonna spitball the heating load, as I have above.  Some might say OP needs 6 tons (like two 3 ton units) and 20 kW strips (like 10 kW in each air handler).  Others (fearing a call back) might spec in 8 or 10 tons (two 4 or 5 ton units) and 30 kW of strips (two 15 kW strips, 150A).

I"m saying the 6-7 tons (two 3 ton units, or a 3 upstairs and a 4 downstairs) and 15 kW total strips is probably fine.  Higher tons will get you a lower balance point, and save operating cost (less strip calling).  

OP...what is your AC tonnage (its on the compressor label)  Its probably 3 tons.  This tons heat versus tons AC is why you need a variable speed compressor and more ducting.  Its (possible) that you wire the two units so the upstairs unit is covering most of the AC (hot humid air enters at the top, and cool dry air falls) and get away with single or dual speed units.  Maybe.

Don't worry about ducts in the attic...get them **masticked** so they don't leak, wrapped in code-level insulation, and bury them.  I had to tear mine upon to mastic them after install (seriously), but then found I was losing <2% heat on my longest run.  If your installer doesn't mastic ducts in the attic...look for a new installer.

You still need to call an electrician to confirm your service wiring is 100A, not just your box.  Or you can read the gauge off the wiring and post it here.  If you are limited to 100A service, then you are looking at fixing the boiler, wiring it as a second stage, and putting in heavy wires to the air handlers, but no or dinky strips (to take the chill off).  And as said, burning 100 gallons during the summer to keep the boiler from leaking?  Or you can bite the bullet, get a new service run and a 200 A panel, and be ready for the future.

When you get quotes... share the tonnage and total kW strip they say you need...

Cheers.


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## woodgeek (May 21, 2021)

So yeah, again, I did all this in 2009-2012.  

I ran for two seasons with on a new HP (ducts in attic) the old oil boiler as a second stage, while improving my envelope.  They installed 15 kW strips (and a new 200 A panel) which only got called on defrost (not wired to the tstat at all).  My guy put in 100 A wiring and breaker (!) worried that I would come back and need bigger strips.

My oil demand plummeted, and I could estimate break even temps by when the second stage got called (which improved as I improved the envelope).

I was still using the oil boiler for HW 12 mos a year.

In 2012 I tore out the old boiler and tank, put in a HPWH and hooked up the strips as the second stage by moving a small wire behind the tstat.  And I was all good.


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## NoGoodAtScreenNames (May 21, 2021)

Thanks @woodgeek - that’s a lot of great info to think through. You are correct. We’ve been shutting down the boiler in the off season. Usually comes on in December and off in March - though I probably do it too early and end up turning it back on during some cold spells. Early spring can be tough. It’s 55 and rainy, the house feels cold and I’m not turning the burner back on but it’s too warm for a fire. This is where a heat pump would really help for comfort (or tbh just sucking it up and keeping the boiler on more).

For the service, upgrading was an option last year when we went with solar. The panel is compatible with a new 200 breaker in and I think the wiring from the meter to the box is also upgraded with 200 amps in mind. The issue is the cable size from the transformer to the house and specifically the conduit that it is in. They said it is undersized for a 200 amp cable by at least a half inch by code.

I’m meeting with someone later today. I’m going to pull some of your and @EbS-P numbers to make myself sound a lot smarter on this stuff than I really am.


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## NoGoodAtScreenNames (May 21, 2021)

I don’t see tonnage on the AC condenser. My main takeaway from the label is that it’s really old and uses the old refrigerant. So other than switching out capacitors this is one repair away from the junk yard.


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## woodgeek (May 21, 2021)

Separate from all this, do some reading on 'attic airsealing'... older houses (pre 2000) typically have several square feet (!) of openings between the conditioned space and the attic, and that alone contributes* 20-30%* to total winter heating demand/bill.   I got that fixed when I did my oil to HP swap and it made a HUGE difference on my winter comfort (draftiness). summer comfort (humidity) and bills.

Tells: You say you have R-49 attic insulation, and no air handler up there.  
--In the winter, an R-49 insulated attic should have NO snow melting on the roof.  That is, the snow on an R-49 roof should melt at basically the same rate as the snow on the ground in the same sun.  If yours melts faster than that (or gets a joist pattern showing through) you do not have an 'R-49 attic', you have conditioned air just blowing through all that fiberglass.
--In the summer, if you turn off your AC at noon on a warm sunny day, the upstairs floor in a house with an R-49 attic should not get uncomfortable very fast.  Like maybe rise a few degrees by the late afternoon and not get noticeably humid (even when the attic is roaring at 120-130°F).  If it is heating up faster, you have superheated and humid attic air getting pulled down into the framing through gaps in the attic. 

Attic airsealing is either a large DIY or a small trained pro project.  If you have a big open flat attic, it will be relatively easy/cheap to do and have a very fast $$ payback.  I'd get it done before installing ducts, tbh.


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## woodgeek (May 21, 2021)

NoGoodAtScreenNames said:


> I don’t see tonnage on the AC condenser. My main takeaway from the label is that it’s really old and uses the old refrigerant. So other than switching out capacitors this is one repair away from the junk yard.



Googles the model # and came up dry.  ACs in New England don't get much use and can last a LONG time.  

If you DON"T upgrade the service:
Get a new boiler, you could also 'drop in' a new single speed (cheap) HP (and **variable speed** airhandler) on the **existing** AC ductwork.  You would max size the unit to the existing ducting, and skip the strip heater.  Get a smart stat that calls the HP when outdoor temp is above 35-40°F, it could probably keep up.  No defrost cycles, no cold blasts.  Smart stat will then run 100% oil at lower outdoor temps.  

The HP will use LESS amps per ton than your existing AC...bc its more efficient.

You could 'play' with the switchover temp to set it lower and see how low it can carry you and if you care at all about defrost cycles.  Lower temps would save more oil.

Given that the heat pump and oil boiler would both last 20+ years, you'd be baking in an extra few hundred tons of CO2 emissions, if you care.


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## NoGoodAtScreenNames (May 21, 2021)

woodgeek said:


> Separate from all this, do some reading on 'attic airsealing'... older houses (pre 2000) typically have several square feet (!) of openings between the conditioned space and the attic, and that alone contributes* 20-30%* to total winter heating demand/bill.   I got that fixed when I did my oil to HP swap and it made a HUGE difference on my winter comfort (draftiness). summer comfort (humidity) and bills.
> 
> Tells: You say you have R-49 attic insulation, and no air handler up there.
> --In the winter, an R-49 insulated attic should have NO snow melting on the roof.  That is, the snow on an R-49 roof should melt at basically the same rate as the snow on the ground in the same sun.  If yours melts faster than that (or gets a joist pattern showing through) you do not have an 'R-49 attic', you have conditioned air just blowing through all that fiberglass.
> ...



Yup - did all that. Pulled up 20 sheets of plywood flooring, pulled up each and every bat of old insulation looking for holes (found a ton all over the place). Reinstalled insulation and built a platform higher to add another layer. Also added a radiant barrier on the rafters. Huge difference from before. I was skeptical of the radiant barrier working but it was pretty cheap and works well. Top surface of the insulation is only about 100F on a typical summer day.


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## EbS-P (May 21, 2021)

NoGoodAtScreenNames said:


> I don’t see tonnage on the AC condenser. My main takeaway from the label is that it’s really old and uses the old refrigerant. So other than switching out capacitors this is one repair away from the junk yard.


Google your  model number.  I’m guessing the “48” in it is 48kbtus or 4 tons.
Evan


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## woodgeek (May 21, 2021)

EbS-P said:


> Google your  model number.  I’m guessing the “48” in it is 48kbtus or 4 tons.
> Evan



NICE.  If the AC is that BIG (sized in 1990 for a big drafty house), the ductwork might take a new 4 ton HP as a drop-in to the existing system.  That could probably carry the house in winter (now that its airsealed,  and better insulated) down to 30°F.

I'm almost wondering if you can patch up the oil boiler, and do a 4 ton HP 'drop in' (no new ductwork or strip wiring or service wiring required).

And you can then decide between replacing the oil boiler with new, or going to all heat pumps NEXT YEAR. 

I assume the existing AC air handler is in the basement and putting most if its air into the lower story.  Going 'all HP' next year would then require probably a second HP (probably 3 tons) and new (but simple and cheap) ducts in the attic, strip+wiring installation (for BOTH HPs) and $$$ service upgrade.


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## EbS-P (May 21, 2021)

woodgeek said:


> I'm almost wondering if you can patch up the oil boiler, and do a 4 ton HP 'drop in' (no new ductwork or strip wiring or service wiring required).


For your use case this really seems like the way to go.  They will always want to sell you more.  there just is not enough profit in it for them to put any real time in designing the perfect system.  To be honest most would not want to pay that extra that extra premium. So that leaves us, the consumer that really cares in the uncomfortable position of telling the contractors what they should be looking at to install.  

The second upstairs zone could be a separate system down the road. If you get at minimum a two stage compressor and replace a 4 ton with a 4 maybe 5 ton that runs 3-4 tons on the low stage you could just add the 2nd floor system later and not use the second stage until it gets really cold.  Variable speed air handler are nice not sure I posted this but mine has a feature that’s called enhanced mode. Ramps up slow and stays at 80% for first 8 minutes then ramps too 100% when second stage is called. Allows you to run. Higher cfm per ton say 400 maybe 450 but only when it’s really needed.
Look for a thermostat that has 3 stages of heat and 2 cooling.  Don’t mess with the Nest smart thermostats. My hvac guy said they have been a huge source of issues.  
Evan


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## NoGoodAtScreenNames (May 21, 2021)

The guy I met today recommended a single zone unit from Bosch.

Bosch BVA60WN1M20 Air Handler

BOVA60HDN1M20G Condensing unit

As expected he really down played the ability of heat pumps to keep up with very cold weather and was inclined to keep the oil as a backup / no electric heating coils now, though they can be added to the unit later. Also didn't get the warm and fuzzies (or cool and fuzzies in this case) on AC performance upstairs. Flow will be lower and coming out the floor registers the air will want to sink back downstairs. Hopefully he's under-promising and over delivering...

Installed cost is 16K and that doesn't do anything for my boiler situation... I assume this single zone / no coils option is going the most bare bones so the cost isn't making me too enthusiastic - especially if there's not a great performance impact during the summer upstairs where it gets hot and muggy.

Still need to get a cost from the guy who talked about a separate handler in the attic.


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## woodgeek (May 21, 2021)

Huh.  Seems a bit high given the (online) hardware price is only $4k.

My whole system change (with 200A box upgrade, all new ducts, and strip wiring) was about $10k in 2008.

I assume the quote is high bc of new ducting?  That is, that this is not a 'drop in' replacement using the old AC ductwork (and probably wiring).

I wouldn't worry much about the AC tbh.  Most installers are used to folks with unairsealed attics with a LOT of upstairs heating load.

Existing AC registers are mounted where?  50:50 upstairs and down?

In general a HP is only marginally more expensive than an AC unit of the same tonnage, for the unit.  Its the wiring stuff (strips and box upgrades) that make it more expensive.


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## EbS-P (May 21, 2021)

Man that price is 5k more than I was thinking.  I guess if you are keeping the oil running, how much could you save with save with a 4 ton two stage American standard unit.   or if you need higher efficiency to get the rebate maybe this.  18 seer American Standard 5 ton  https://ashp.neep.org/#!/product/25753.   Really If its rated at 41k BTUs at 5 degrees I don’t see why you would need heat strips. that Bosh unit may have better efficiency but has 6k less btus Than the AS unit At 5df.  I like shopping for this kind of stuff, I hate having to make the final decision
American standard are just rebranded Trane unit.  FYI. 

if the rebates are still available and you can get by this summer with  your current AC it might make sense to wait on this awhile.    The supply chain is just so messed up right now.

my dad just did the math here for our weather and the extra money for the more efficient unit just didn’t make money sense. So he went single stage 14 seer.   Your heating degree days are  probably 3x our cooling degree days.

to put it in perspective I was quoted 6000$ for a single 2 ton mini split that  was an easy install in a basically unfinished basement.  

evan


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## velvetfoot (May 21, 2021)

How much life is left in the oil boiler?  My oil boiler runs as a cold start and I have a large (120 gal) indirect dhw/buffer tank, (which doubles as a buffer tank for a pellet boiler, but that's another story), on its own zone.  I also have an electric and heat pump water heaters, along with the pellet boiler, but I've been only burning oil, partly because of the price of oil going down, (that's changing), laziness, noise, and ease of power outage use, as I said earlier.  I'm also of the opinion, based on the observations during my own oil boiler maintenance, that keeping the boiler running for a longer time to heat that well-insulated buffer tank, is better than cycling it a lot.


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## NoGoodAtScreenNames (May 22, 2021)

The quote was to use existing ductwork. I wonder if there is a little bit of rebate confiscation going on. If they approved a 5 ton unit for the full rebate that’s $5,000. So they may think my budget is higher instead of letting me benefit from the rebate savings.

I think I’m going to try fixing the boiler which should be about $1,500  if it works. This would then be a replacement for my poorly running AC with the benefit of providing heat. I can run it for a few seasons to see how it does in cold weather and then when the boiler truly does die decide to upgrade to heating strips for extreme cold days, replace the boiler or upgrade the heat pump to whatever the tech is available then. Most likely it would be upgrading the electrical service and putting heating strips. Don’t forget I burn wood and plan to do that for as long as I can.  Anything after the heat pump is my second backup after wood.


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## EbS-P (May 22, 2021)

NoGoodAtScreenNames said:


> So they may think my budget is higher instead of letting me benefit from the rebate savings.


I might ask for a quote on the cheapest non rebate eligible system too.   I just don’t see you running the system enough to make up the cost difference between the cheap- less efficient system vs the expensive-really efficient one.  It would be different if you didn’t burn wood. 

Evan


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## woodgeek (May 22, 2021)

Makes sense. I agree about the confiscation...

I live in a HCOL area, and I find that **simple** installs usually come in at 2X the online hardware cost.  That would be $8-9k in your case for a simple drop in.  + $5k rebate gets to your ballpark.

Get more quotes.  Or get a quote for a 4 ton AC replacement, and then up the quote to HP without any strips.  It shouldn't be much more.

Ductwork for a 4 ton AC is probably a bit too small for a 5 ton HP... with a single speed compressor, running too high cfm for the ducts will make for a lot of air noise.  Right sizing it will be reasonably quiet.   If you existing ductwork is OK and quiet at 4 tons, it might be ok at 5. But I still think 4 tons would be enough for shoulder (>35°F with oil doing 100% of colder). 

-----------------------

Oh, new idea... which I think you are already thinking...

5 tons (with current ducts up and down MIGHT be enough to cover you reasonably with strip heat backup).  So you could install a 5 ton on existing ductwork with the patched boiler kicking in below 35°F.  You can test it out (by playing with the tstat) to see how low it goes, and if it does OK (like down to 20°F or something), then just pull the boiler and add strips WITHOUT adding another HP.

I'll tell you two things...the 'cold blast' defrost thing is not an issue during dry weather, it is only bad when its snowing and the coil is getting packed with snow.  So you could test the HP to your heart's content during dry weather and prob not even notice the defrost (the unit will defrost FINE without strips, the heat comes from conditioned house air).

I will tell you that if you DO try to run on HP only in cold weather, some rooms will get colder than others (esp with a one-zone two story setup).  I ended up adding a couple branches to my ductwork over time to even that out.  This has the advantage of increasing the cfm capacity of the ductwork (resolving the too small current ductwork issue).

As a woodburner, you probably don't care much about heating balance in the dead of winter anyway.  The house won't freeze unattended with a 5 ton HP.

The only problem here is that a 5 ton HP might have poor dehumidification in summer AC, cool humid air is not comfortable.  I'd get at least a two-speed compressor and variable speed blower to help with that, a small upcharge.


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## NoGoodAtScreenNames (May 22, 2021)

The current AC is pretty loud. I threw it on today and it’s a base line 60 db on a first floor room. The booster fans for upstairs are loud and rickety when they are on. All in all it’s kind of sounds like riding a subway. I often turn it off just because the sound gives me a headache. That and the fact it doesn’t work very well make me want to replace it. I like the guy who wanted to put two units in since he talked a lot about running them low and constantly to improve humidity levels. Even when it is somewhat cool upstairs it’s still muggy.

follow up note on the insulation. Today was the first real summer  like day. 85F going to 90 in a few days. We had the windows open and it’s been comfortable. 75 downstairs, 2nd floor walls at eye level were 78. Second floor ceiling 78. Top of attic insulation 95. Roof sheathing 130 behind the radiant barrier. Putting some effort into the attic definitely helps.


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## EbS-P (May 22, 2021)

I got one of these to monitor temp and humidity in my crawl space this summer. It’s a neat gadget.

  Limited-time deal: Govee Hygrometer Thermometer, Wireless Thermometer, Mini Bluetooth Humidity Sensor with Notification Alert, Data Storage and Export, 262 Feet Connecting Range Amazon product


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## woodgeek (May 22, 2021)

Yeah, a single zone HP with a two speed compressor (and adding some brach ducts in the basement to reduce the noise and improve the balance (which is DIY-able) is the 'cheap' option, but it would work OK.

I've got a single zone HP with single speed compressor and balance is OK bc I run a strategically placed ceiling fan 24/7 in the winter.  A bit of a kludge, but comfortable.  When the HP dies, my next one will be variable speed compressor,  to run low and slow and quiet in the shoulder seasons.

The two zones and HPs, up and down, would be VERY nice, quiet, and will be the most efficient (bc it will have more tonnage, and run at lower speed).  But it will cost $10k more.


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## maple1 (May 23, 2021)

From an earlier post it sounded like the problem with the oil boiler was leaking around the DHW coils? That's minor, if so. Mine did that a couple times over the time I had it. I just replaced the coil gasket. First time i did it i installed unions to make it an easier job in the future. But not clear if that is the problem or not. Or exactly what you have for a boiler. Oil boilers usually can last a very long time. The burner could be another story.


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## begreen (May 23, 2021)

NoGoodAtScreenNames said:


> The current AC is pretty loud. I threw it on today and it’s a base line 60 db on a first floor room. The booster fans for upstairs are loud and rickety when they are on. All in all it’s kind of sounds like riding a subway. I often turn it off just because the sound gives me a headache. That and the fact it doesn’t work very well make me want to replace it. I like the guy who wanted to put two units in since he talked a lot about running them low and constantly to improve humidity levels. Even when it is somewhat cool upstairs it’s still muggy.
> 
> follow up note on the insulation. Today was the first real summer  like day. 85F going to 90 in a few days. We had the windows open and it’s been comfortable. 75 downstairs, 2nd floor walls at eye level were 78. Second floor ceiling 78. Top of attic insulation 95. Roof sheathing 130 behind the radiant barrier. Putting some effort into the attic definitely helps.


I grew up back east in a house with no AC. We opened up the windows in the evening to let in the cool night air and closed them in the morning.  We had a whole house fan in the attic gable with a ceiling vent that helped pull in the cool night air too. This worked reasonably well except on the hottest, muggiest days.


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## NoGoodAtScreenNames (May 23, 2021)

It’s a Burnham and yes leaking from the dis-used tankless dhw coils and around the faceplate.  Suspect since it hasn’t been leaking too long that most of the corrosion is just sediment from the water accumulating and that the fasteners are in repairable shape. You never know till you try and you don’t try unless you know what you are doing.

We once had a family friend over who is a plumber and I was showing him the crazy labyrinth that is necessary to run two different water heaters seasonally. I pointed to a valve that looked in totally good shape and he he yells “Don’t touch that Since you’re not a plumber you are only allowed to touch that twice a year, once when you turn it on and once to turn it off. Even better, call me and I’ll turn it for you”.  Little does he know I turn all the valves once a month to make sure they don’t get stuck...  but this is boiler thing is out of my league.


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## NoGoodAtScreenNames (May 23, 2021)

begreen said:


> I grew up back east in a house with no AC. We opened up the windows in the evening to let in the cool night air and closed them in the morning.  We had a whole house fan in the attic gable with a ceiling vent that helped pull in the cool night air too. This worked reasonably well except on the hottest, muggiest days.



Yes, when it’s reasonable out at night I often open the door to the attic stairs and open the windows on the table ends of the attic. I then have a few window fans blowing in. Often it’s better to give a place for the warm air to go than to try to cool it off. The humidity can still be tough if you don’t directly feel the air movement from fans though.


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## begreen (May 23, 2021)

The irony is that my dad was a mechanical contractor, but the house was boiler heated so AC would have required a whole new system installed.


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## velvetfoot (May 23, 2021)

Crazy labyrinth?  You ain't seen nothing.  The blue tank came with the system and hasn't been used since I got the other tank.  You got me thinking about draining the electric tank and maybe running it and the heat pump water heater, but I'm also lazy.

My boiler is a 2003 vintage Burnham boiler.  I don't know how long those cast iron oil boilers can last.


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## maple1 (May 23, 2021)

NoGoodAtScreenNames said:


> It’s a Burnham and yes leaking from the dis-used tankless dhw coils and around the faceplate.  Suspect since it hasn’t been leaking too long that most of the corrosion is just sediment from the water accumulating and that the fasteners are in repairable shape. You never know till you try and you don’t try unless you know what you are doing.
> 
> We once had a family friend over who is a plumber and I was showing him the crazy labyrinth that is necessary to run two different water heaters seasonally. I pointed to a valve that looked in totally good shape and he he yells “Don’t touch that Since you’re not a plumber you are only allowed to touch that twice a year, once when you turn it on and once to turn it off. Even better, call me and I’ll turn it for you”.  Little does he know I turn all the valves once a month to make sure they don’t get stuck...  but this is boiler thing is out of my league.
> 
> View attachment 278969



Oooh, ya, that does look pretty crusty.


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## NoGoodAtScreenNames (May 23, 2021)

maple1 said:


> Oooh, ya, that does look pretty crusty.



Yeah. And that is from about 1 year since I first noticed some dampness. During the heating season it was evaporating so I couldn’t see any leak but still corroding and building up all the crunchiness.


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## EbS-P (May 24, 2021)

Have you checked out the MR Cool systems. They are very intriguing.  I still don’t have a good assessment of the quality versus cost and if they are a good investment but it’s product that’s out there. They claim 100% heat output down to -5F. (I think I saw that somewhere). 









						4 to 5 Ton 18 SEER MrCool Universal Central Heat Pump Split System - Upflow/Horizontal
					

The 4 to 5 Ton 18 SEER MrCool Universal Central Heat Pump Split System is one of the most high performing, versatile, and simple heating and cooling products available from the industry today. This is a central heat pump that can cool better than most air conditioners, heat better than virtually...




					iwae.com


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## NoGoodAtScreenNames (May 24, 2021)

EbS-P said:


> Have you checked out the MR Cool systems. They are very intriguing.  I still don’t have a good assessment of the quality versus cost and if they are a good investment but it’s product that’s out there. They claim 100% heat output down to -5F. (I think I saw that somewhere).
> 
> 
> 
> ...



Very interesting video of the performance of just the heat pump with no supplemental resistance keeping a house at 70F while it was -24F outside. They didn’t say how much electricity it was using at the time though. I assume it would have been down near 100% efficient if not below which would mean in a real world application you’d be better off with resistance heat I’d think. But on the other hand it would be nice to know you won’t go cold without resistance heat even if you use a little extra electricity. Either way pretty impressive and breaks some myths about heat pumps (or at least this one) in very cold weather.


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## woodgeek (May 25, 2021)

For the record, the coil plate of my old boiler looked more crusty than that for all the 6 years I owned it, but didn't drip when it was hot.  I just let it stay hot all the time and never got it fixed.

Doesn't seem likely to be the sort of thing that will open up and cause a flood suddenly.  I don't know if I would bother fixing it, and would just use the boiler for a few more years as is, esp if it doesn't drip when hot.

If it makes you nervous, two suggestions:
1. put a pan an a water alarm under it...some of them are now wifi enabled to alert your phone.
2. shut it down when not in heating season and TURN OFF the makeup water supply.  Turn it back on when heating season returns.  When the boiler cools without makeup water, it will relieve the pressure behind the leak, and probably stop a slow leak entirely.  That way there is NO WAY the leak can open up and flood your house, e.g. while you are having a relaxing summer vacation.  Worst case is just gravity drainage of a few gallons of rusty water....which will not happen anyway.

I say go for a 5 ton heat pump, have an HVAC guy add a few branches (or upsize existing branches) to your ducts to up its CFM capacity 20-30%, to rooms that you think are underserved.  Flex is quieter than hard ducting.  And then run the boiler AS IS 4 mos a year, assuming it doesn't start to drip when hot.   After a season or two getting to know the new HP (e.g. running it with the boiler shut down sometimes to see how low it goes without strips), get a $$$ new service line and strips put in, and the rip out the old boiler.   You can then decide if you want another HP in the attic (or a minisplit in the basement), or to further expand the ducts to the existing unit for better balance/quiet, etc.

And this is basically just what I did 9-11 years ago.  Except you already have the HPWH.


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## begreen (May 25, 2021)

NoGoodAtScreenNames said:


> The guy I met today recommended a single zone unit from Bosch.
> 
> Bosch BVA60WN1M20 Air Handler
> 
> ...


I would be leery of getting the Bosch. They make some good tools, but are not known for HVAC. If they abandon this market you could be left out of luck when service or parts are needed.


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## peakbagger (May 25, 2021)

I am on a few industry mailing lists and every worldwide firm is jumping on the bandwagon to sign up HVAC firms to sell their product that they probably are already selling somewhere in the world. There are also a few US firms trying to get their foot in the door. Everyone assumes that the federal government and utilities will be subsidizing retrofits heavily. Its a potential gold rush and no one knows who will shake out.  No doubt the Chinese will rush in with copycat low price equipment and undercut all the big name firms. The trick with all this equipment is its more complex than its predecessors and potentially need more skilled maintenance by folks with access to factory parts and service manuals. Local HVAC firms are making their bets on who they want to be in bed with in the long term. 

Another aspect is the current HCFC being used in most equipment is being phased out and it doubtful its replacement will be drop in. Good chance ten years out, when the current units start to fail it will not be worth fixing them.


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## Prof (May 25, 2021)

NoGoodAtScreenNames said:


> The guy I met today recommended a single zone unit from Bosch.
> 
> Bosch BVA60WN1M20 Air Handler
> 
> ...


Holy cow! I had the same unit installed last summer for $6500, including new ducts in the basement. It looks like the units went up a bit in price, but no where near the cost difference. That being said, I couldn't be happier with the Bosch system. The bump to my electric bill has only been about $20-40/mo for cooling. Used it for heat in the shoulder season, and didn't notice much increase in electric bill then either.


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## Texas123 (May 25, 2021)

Surely there are some on line HVAC load calculators which can be used? I mean you need to know the heating and cooling loads and then add a few percentages. Down here in Texas the rule of thumb is one ton (12000) BTUS of heating or cooling for each 500 square feet.


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## semipro (May 25, 2021)

Texas123 said:


> Surely there are some on line HVAC load calculators which can be used? I mean you need to know the heating and cooling loads and then add a few percentages. Down here in Texas the rule of thumb is one ton (12000) BTUS of heating or cooling for each 500 square feet.


Poor assumptions about HVAC needs have caused a lot of problems with improper dehumidification and resulting mold issues.  Usually with the idea that "bigger is better".  
Relatively simple calculations of heating/cooling loads and required system sizes can be done using well know prescriptive references such as "Manual J". 
A good reference here: https://www.energyvanguard.com/blog/hvac-design-done-right-manual-j-s-t-d/


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## begreen (May 25, 2021)

Prof said:


> Holy cow! I had the same unit installed last summer for $6500, including new ducts in the basement. It looks like the units went up a bit in price, but no where near the cost difference. That being said, I couldn't be happier with the Bosch system. The bump to my electric bill has only been about $20-40/mo for cooling. Used it for heat in the shoulder season, and didn't notice much increase in electric bill then either.


The Bova 2 is more efficient than the Bova 1. Looks like Bosch developed these units in China with Midea.


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## EbS-P (May 26, 2021)

semipro said:


> Poor assumptions about HVAC needs have caused a lot of problems with improper dehumidification and resulting mold issues.  Usually with the idea that "bigger is better".
> Relatively simple calculations of heating/cooling loads and required system sizes can be done using well know prescriptive references such as "Manual J".
> A good reference here: https://www.energyvanguard.com/blog/hvac-design-done-right-manual-j-s-t-d/


I think that with variable speed compressors and air handlers the manual J will be less utilized and installers will go with their gut feelings then add a ton and call it good.  My dad could not get any he was getting quotes from to do a manual J. He even offered 250$   They just asked if the old system did ok and kept the same size.  I have tried the online free tools. I never got very good results. I rushed through and it always over calculated the load.  The the shade, maybe I underestimated wall insulation, the 3/5 daylight basement basement and the crawl space.... just to many variables.  Or maybe I just like the house temps different than design spec.  

For installs we’re heating demand is more than twice cooling I really think variable speed compressor and air handler are the way to go.  My two stage handles all but the coldest week well but i doubt even then the heating load is twice the max cooling load.  

Evan


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## NoGoodAtScreenNames (May 26, 2021)

The utility rebate is administered by an energy efficiency company. They require pre-approval of the design before the work can begin in order to qualify for the rebate. First step in that is a consultation with customer which for me happened yesterday.

A lot of the same advice I’m seeing here. They were mostly concerned about right sizing the equipment so it can cycle down appropriately for the zone. He also seemed a little skeptical of a drop in place without a good thinking about the existing ducts. At a minimum he said we should reseal all the existing ducts including the hidden runs in the first floor walls going upstairs. He recommended  something like this for the hidden runs:

https://aeroseal.com/

Lastly, he wasn’t as concerned about heating strips. He seemed to favor doing getting something that had good cold weather performance which for my area he said to design for 8F. Like many of you said he thought to use the boiler as the backup and see how it performed in real life and upgrade the service only if needed down the road.


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## woodgeek (May 26, 2021)

I'd be the first to admit you need a pro consultation.  I'd think that to get to 8°F on HP alone you would need more than 5 tons total, which means an upper story and lower story air handler.  A $5k rebate would help alleviate the pain. 

And a 5 ton system on the existing ducts is NOT going to be a simple drop in, bc you would be upsizing the existing ducts, in hopes of saving money.  But at some point on that, there will be diminishing returns.

As I said, the defrost cold blasts are only when the there is snow or freezing rain packing the outdoor unit, actual 'frost' melts pretty quickly and the hot ductwork absorbs a lot of the cold air before it reaches the registers.  If the registers aren't pointed at where you live, you still might not care...or might only notice a few times a season.

But you will need backup, either the boiler or strips.


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## clancey (May 26, 2021)

I am curious and is that Windhager--pellet--a back up system for your boiler in the picture velvetfoot?  A lot of stuff there and I was just wondering? If this is so and I am on the right track here (which I doubt--lol)--do you save a lot of money by having the pellets over the oil and why the two systems?  c


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## velvetfoot (May 26, 2021)

clancey said:


> I am curious and is that Windhager--pellet--a back up system for your boiler in the picture velvetfoot? A lot of stuff there and I was just wondering? If this is so and I am on the right track here (which I doubt--lol)--do you save a lot of money by having the pellets over the oil and why the two systems? c



As I alluded to earlier, I haven't been using it since the price of oil went down and pellets did not.  What you can't see is 6 tons of pellets on pallets off to the right.  It was a project after I did right after I retired.  I originally wanted a wood boiler, but I ran into a snag with getting a propane tank for storage.  Oddly enough, I'm getting a 1000 gal tank for the gen delivered on Tuesday, but as I said, it's a rental, lol.


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## clancey (May 26, 2021)

Yea okay that makes sense---good for you...thanks c


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## semipro (May 27, 2021)

woodgeek said:


> As I said, the defrost cold blasts are only when the there is snow or freezing rain packing the outdoor unit, actual 'frost' melts pretty quickly and the hot ductwork absorbs a lot of the cold air before it reaches the registers. If the registers aren't pointed at where you live, you still might not care...or might only notice a few times a season.


I'd agree with all of this but I'd note that the outside coil on our Mr. Cool Universal will freeze up when the humidity is high regardless of precipitation (of course maybe that's what you're referring to re frost).   Ours is located where it's not exposed to rain, snow, etc. and the coils still freeze up.
The cold blasts of air from the registers are a minor nuisance and the reverse cycling of the HP to defrost reduces system complexity and lifetime costs.


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## sesmith (Jun 2, 2021)

Have you checked with anyone who does ground source heat pumps?  Likely more money up front but would be an ideal solution so long as you find an installer who knows what they're doing.  We put one in our previous house up north here.  I'd do it again.  Best heating system we ever had.  We now live in SC in the winter months.  There it made sense to do a new more efficient air source heat pump.  But up north here, I wouldn't do air source unless they're getting as good on the low end now as the minisplits are doing.  You'll end up spending a lot of the winter with the heat strips running.  With ground source you don't have that issue.  Properly sized, you'll use the aux strips very little.    Ours was extremely efficient.  We actually quit burning wood in that house as I wasn't cutting it myself anymore, and it would have cost more to heat the house with wood than with the heat pump if I had to buy firewood.


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## peakbagger (Jun 3, 2021)

Ground source heat pumps can be very efficient but its a function of if the house was designed for low supply temperature heating.  Air based systems have to have larger ducts installed in conditioned spaces  while hydronic systems need properly designed and installed radiant heating or lots of radiant emitters. It comes down to if a house is set up for 85 deg F supply temp and the ground source is 40 to 50 degree F year round the COP is very high compared to air source unit which may need to deal with 0 deg F. 

The down side is bit up front cost to drill the wells or install the ground loops. The very general number in my neck of the woods is 300 feet of well for one ton of heating. Unless someone is doing a lot of excavation, ground loops (slinky style) are also expensive and have some issues where the ground source can start to run out of capacity and start to cool down in heating season and heat up in cooling season. These also tend to be complex custom systems where technicians have to be well trained. In my rural/vacation area many of the techs end up driving up from the more urban areas and maintenance and  repairs are expensive.  I have talked to local firm that does a lot of geothermal (mostly heavilly subsidized) and they are not interested in 2 to 3 ton install, they start getting interested above 5 tons.

For a new house, there is lot to be said for spending the money for complex heating and cooling system on upgrading to a Passivhaus or Pretty Good House design and minimize both heating and cooling to the point where the systems are quite small.  Add in some solar panels and net metering, and those homes can easily be net zero even in cold climate. The best heating and cooling costs are the ones you do not need to spend by designing in low heating and cooling demand.  Unless someone is willing to gut a place, super-insulating and low supply temps are hard to retrofit.


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## sesmith (Jun 3, 2021)

Yes.  Can't agree more.  In his case, I'm sure his duct system would need to work to handle the extra flow needed for a heat pump system.  Once done, he would have super efficient ac and heat.  Can't stress enough that you need to find an installer who knows how to engineer and size the system.  Good design is super critical for geo systems, or bad things happen.  Ours was done in trenches, not slinky style though.  We had plenty of space that they did straight lines in the loops.  Never had any issues with capacity.  We did have to replace all our ducting and increase capacity.  I do miss that system.  It was way quieter than the heat pump system we have in our SC house.  Don't miss the cold weather, though.


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## begreen (Jun 3, 2021)

sesmith said:


> It was way quieter than the heat pump system we have in our SC house.  Don't miss the cold weather, though.


Time to change the avatar location?


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## sesmith (Jun 3, 2021)

Well...yes and no.  We retired a couple of years ago.  Sold the house and moved to another one in SC.  Kept a piece of forest land we had 4 miles up the road from our old place and put a cabin on it.  So from spring to fall we alternate between the cabin in central NY, and a boat on the Great Lakes.  It's a rough existence, never knowing where we belong, but someone's gotta do it.  I still get my wood heating fix in the shoulder seasons at the cabin, but once the snowflakes fly, we're outta there.


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## maple1 (Jun 4, 2021)

Geo can be a very hard thing to justify if retrofitting. I looked into it 10 years ago just before my boiler swap. Would have been 20k for the in ground and heat pump side, and somewhere between 10-20k more for a distribution system overhaul. Also had a couple friends tell me their power bills ended up being quite a bit higher than they were anticipating. From pumps running 24/7, I think. But maybe their anticipations weren't realistic.


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## peakbagger (Jun 4, 2021)

maple1 said:


> Geo can be a very hard thing to justify if retrofitting. I looked into it 10 years ago just before my boiler swap. Would have been 20k for the in ground and heat pump side, and somewhere between 10-20k more for a distribution system overhaul. Also had a couple friends tell me their power bills ended up being quite a bit higher than they were anticipating. From pumps running 24/7, I think. But maybe their anticipations weren't realistic.



My limited experiences is that there are a lot of good geothermal salesmen . Our state was throwing a lot of money for incentives and unrealistic promises were made. Lots of summer places were built that looked good but lots of glass, open fireplaces,  square footage with suspect attention to detail for energy efficiency all mean that these homes are relative energy hogs so even if there method of heating is more efficient its still a steep bill. The other aspect is that as seasonal homes the temptation is to keep the temps low during non occupied periods and then crank it up when the owner shows up to use the place. Low supply temps means slow heating response so there are usually far less efficient auxiliary resistance heaters in the system to augment the geothermal heat.


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## sloeffle (Jun 4, 2021)

peakbagger said:


> My limited experiences is that there is lot of good geothermal salesmen .


I couldn't agree with you more. When I bought my geo system I had a guy tell me that I needed 200' of pipe in the ground for every ton. I had friend that took that advice, and he said his heat strips come on quite often.  The system I have now has 600' of pipe in the ground per ton. Slinky vs well vs horizontal pipe is another debate I had also.


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## sesmith (Jun 4, 2021)

peakbagger said:


> My limited experiences is that there is lot of good geothermal salesmen .



Unfortunately, that's been the case.  Luckily, our installer was an engineer who knew how to design systems, and ours worked out even better than his predictions.  He was able to calculate up front just what it would likely take in kwh to heat our place and cool it, and heat water.  How do you find a guy like that?  I have no idea.  I worked with his dad (also an engineer), so based on that, he was our guy.  Not sure what the incentives are now, but when we installed ours the payback was about 7 years over oil (federal incentives included).  Unfortunately, the incentives and the hype made too many installers who shouldn't have got in the game "geo experts".  Many of those went out of business leaving customers on the hook with marginal systems.  Not sure if the playing field has weeded out the bad ones yet.  Like anything else you contract out, you have to do some research on the product and background check the contractor.


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## EbS-P (Jun 4, 2021)

sesmith said:


> Unfortunately, the incentives and the hype made too many installers who shouldn't have got in the game "geo experts". Many of those went out of business leaving customers on the hook with marginal systems


I am getting the sense that this is happening with solar installations now.  Had a guy come over and say “oh your north facing roof is pretty flat let’s put 12-15 panels there” this was after I have to break out my compass to convince him what direction north was


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## sesmith (Jun 4, 2021)

It is down in my area of SC.  Solar took off the last few years.  They used to have reps at Home Depot to try and sell you (before covid).  I can't believe some of the crappy shingle roofs they put panels on that should have been reroofed prior to installation.  Also can't believe the shading issues on some of the installations I've seen.


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## NoGoodAtScreenNames (Jun 16, 2021)

So I got another quote. This was for two 3 ton carrier units. One in the basement with with the existing duct work (cutting off the lines to the second floor) and another unit in the attic with insulated duct work for ceiling registers… $40K and that does not include upgrading to 200 amp service. As much as I’d like to get off fossil fuels, if I took the boiler replacement quote for $10k that’s $30k in heating costs to save with a heat pump before I break even. Burning wood, I don’t burn a lot of oil - let’s round up to $1,000 to make numbers easy. A true all season heat pump will take 30 years to pay off?  As a retrofit I’m not sure anyone would ever take that deal. 

Granted at some point I’ll need a new AC but I’d be better with the drop in Bosch for $15k, though I’m suspicious the existing ductwork won’t work well that option…

So I guess at this point I’m leaning towards fixing the boiler if it can be done and let it ride on the AC as long as I can. It’s sad, I’m the type of person who might otherwise pay a little extra for the green option, but I just can’t justify that with the amount of oil I actually burn through.


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## EbS-P (Jun 16, 2021)

NoGoodAtScreenNames said:


> $40K and that does not include upgrading to 200 amp service.


That’s steep. What are the odds those units last 30 years?  So what if the duct work isn’t great, a  5 ton ac/heatpump replacement would carry you a long way for a long time with the wood stove.    I agree spending money in the boiler as a backup to the future cheaper heatpump is the way to go.  Plant a few more trees, buy some carbon credit or hang all your laundry on the clothesline  what ever makes you feel better about still running the boiler.  I think that’s the best decision. Personally I chose the clothesline.  7 big loads a week adds up.  
Evan


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## Prof (Jun 16, 2021)

Holy cow! Yeah, I couldn't justify that type of price difference for the green option.


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## begreen (Jun 16, 2021)

I think repairing the boiler is a good option, regardless. Then you have baseload heating covered. The woodstove is gravy on top.


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## NoGoodAtScreenNames (Jun 17, 2021)

EbS-P said:


> That’s steep. What are the odds those units last 30 years?  So what if the duct work isn’t great, a  5 ton ac/heatpump replacement would carry you a long way for a long time with the wood stove.    I agree spending money in the boiler as a backup to the future cheaper heatpump is the way to go.  Plant a few more trees, buy some carbon credit or hang all your laundry on the clothesline  what ever makes you feel better about still running the boiler.  I think that’s the best decision. Personally I chose the clothesline.  7 big loads a week adds up.
> Evan



At that price if I was just trying to throw money at reducing my carbon foot print I’d be better replacing my car with a BEV.

Thinking again about the drop in with the existing ducts. How much does the air handler location matter?  Right now it’s in the basement on a far gable end. I would think tying it in at a more central - maybe 15-20’ more towards the center of the house may help ?


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## begreen (Jun 17, 2021)

NoGoodAtScreenNames said:


> Thinking again about the drop in with the existing ducts. How much does the air handler location matter? Right now it’s in the basement on a far gable end. I would think tying it in at a more central - maybe 15-20’ more towards the center of the house may help ?


Design-wise that would be an improvement, but it most likely would require a redo of the trunk ducts which usually taper down in size as air supplies are taken off the main trunk. That could get costly.


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## NoGoodAtScreenNames (Jun 18, 2021)

begreen said:


> Design-wise that would be an improvement, but it most likely would require a redo of the trunk ducts which usually taper down in size as air supplies are taken off the main trunk. That could get costly.



Yeah - I was talking to the guy who first recommended patching the boiler and doing two units. He hasn’t quoted the heat pump yet, but he was basically recommending to hold off on anything for right now other than fixing things that are broken. He said the sheet metal costs alone are turning a 12k job into a 15k job, plus manufacturers are raising prices due to supply problems. I imagine most jobs now are non discretionary commercial and new builds that were already in the works.


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## woodgeek (Jun 20, 2021)

$40k is robbery IMO.   I still like the idea of patching the boiler, and dropping in a (size matched) HP on the existing ductwork, with no defrost circuitry, and using it for AC and shoulder season heating.

Anyone who want more than $12k for a drop in conventional HP is IMO ridiculous.

Ofc, the current environment is jumping costs, waiting is probably a good idea too.


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## NoGoodAtScreenNames (Dec 12, 2022)

So I’m back and I think I’m going to try to pull the trigger sometime before next summer. My original post has the details if you don’t want to reread the whole thread.   

We were able to patch the oil burner pretty inexpensively. So I’m not looking for a heat pump that will have to carry the whole house in extreme cold temps. My new goals probably in this order. 

1) Replace the current 40 year old outdoor unit so it doesn’t die on a hot summer day.

2) Improve AC performance upstairs

3) Have shoulder season heating that can keep up to about 40F. At that point I’m fine with burning wood or oil. If the heat pump can still help out with some btus below that - great but not necessary. Rebates of $1k per ton plus whatever IRA incentives that may apply make it seem crazy to do just an AC. 

I’m going to start talking to contractors again. I’m thinking that keeping an air handler in the basement for the first floor and blocking off the ducts to the second floor is best. Probably a new unit in the attic with either a  single zone air handler or multiple heads. Multiple heads would be the preference I think if not cost prohibitive. 

I’m still restricted to 100 amps but I’m hoping that avoiding resistive heat strips should leave me ok.  Not sure everything can run on one outdoor unit that can ramp up / down to meet the demand of both floors or if it means two outdoor units. A lower amp option I guess would be preferable. 

Any thoughts or advice before I start talking to folks again? Thanks everybody.


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## EbS-P (Dec 12, 2022)

Advice. 
1 avoid condensate pumps. 
2 Heat pumps work really well in 40+ degree weather.  I just was curious today and my 2009 unit runs a COP of 4 when it’s 52 degrees.   So if you don’t need lots of cold weather capacity don’t spend extra for it.   
3. Can contractor can install  almost any unit but will they air balance it.  I think by code they need to do a load calc.  Ask for it. Pay 200$ to get that the manual s and the manual D.  Get copies.  Why. You want a new unit and want to re use old ductwork nothing wrong there unless the ducts won’t handle the capacity of the new unit. 
4. Wait till the IRA efficiency threshold is set.  It should be out soon. 
5. Im not sold on invert whole house systems and wood heat.  The ROI because we don’t use it much during the winter is much much longer.  Im a fan of the two stage units.  
6. Get in writing the. Units will keep humidity below 55% in the summer.  

100 amp service should be fine.  Smart kid control is a thing now.  My 3 ton systems pulls 3kw max at 240 V. Call it 12-13 amps.  

That said cold weather heatpumps might be a good fit.


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## woodgeek (Dec 13, 2022)

EbS-P has a good list!

I will add that if you wanted to use this as your sole heat source, you would pay for inverter/cold weather tech.  As it is, you won't.  Two-stage compressor is a good get, bc of the summer dehumidification factor (a single speed system won't dehumidify well).  This may be less important if the system is undersized for heating (and thus not super oversized for cooling).  

I would add variable speed air handler.  These are getting almost standard, but they are a must.  They spool up and down slowly, so they are less annoying.  Also helps with dehumidication (bc CFM can be altered).

Also, make sure the return(s) are properly sized, if not as large as possible (oversized).  The air noise on the returns is a major source of overall noise.  And that you can get good 1" low resistance MERV 13+ filters in there.  

The 'weird' thing you are doing is the 'no strips' thing.  The installer will hate that, and assume you will be a callback problem.  What you will see in use is that the unit will cycle in defrost (probably every compressor runhour) when the temps are below ~40°F outdoor.  When this happens the registers will blow COLD air.   Like ice cold.  If there is not much frost on the outdoor coil, this cycle might last 2-3 minutes, and there is enough warm air in the warm ductwork to buffer this... it might just start getting cold at the registers and the compressor is done, and starts pumping heat again.  So, if its 35°F outside and dry, you might not notice/care.  But the installer will assume you (or the Mrs) will HATE this and call him back and complain and demand a refund.

Be aware that the '40°F' number you have is 100% about this.  The HP will work great down to 5°F, and provide loads of BTUs down to 20-25°F even if its not 'cold weather' optimized.  It will just do this 'cold blast' thing every run hour.  The tstats in the unit that call the defrosts are not precision, they are more like ±5°F.  So you could get lucky and get one that doesn't defrost until 35°F outdoor.  Or you could get one that starts at 45°F.  Its a crap shoot, and also depends on how tolerant your wife is.  You can get a LOT more shoulder BTUs out of this if the registers are not directed at where she hangs out.

And even if you don't mind the cold blast under normal circumstances, if it it rainy/snowy/damp out, the compressor will pick up a LOT of ice, and then do a defrost cycle for 8-10 minutes.  And in that case, the cold blast will have everyone asking WTF and the dog hiding.

So you are going to have to experiment.  The actual outdoor temp where frost/ice starts to form is about 35°F.  My guess is that you will get a house stat that locks the HP out at 35-37°F (you will want this control), and that short 'defrost' cycles with no ice on the coil will be bearable.  And the total BTU/$$$ difference between locking out at 35 and 40 will be useful. 

The other thing is that if no one is home (you are all traveling) then there is no problem running the HP to lower outdoor temps, calling the oil as a second stage.  So you could have it wired that way (HP first stage, oil second stage) and then adjust the HP lockout temp to 35° normally, and lower when 'away'.  I don't know of a smart stat that will do that automatically.

Be advised.  The above is for conventional 'split' HPs that would drop into your AC ductwork.  Mini-splits also manage to defrost themselves, without the cold blast and without strips.  I don't know how they do that (presumably feathering the register air  or running at lower speed) but that might be useful in your application.  So an installer might have a tech fix for the above that I do not know about.


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## NoGoodAtScreenNames (Dec 13, 2022)

Thanks to you both.  When we were considering the heat pump as the primary heater earlier in the thread we were talking about high amperage resistant heat to take over a few days a year when it’s excessively cold. I’m not opposed to some coils to help with defrost cycles - but I would just pick the lower amperage ones.


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## EbS-P (Dec 13, 2022)

How long do you want to be in this house?


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## NoGoodAtScreenNames (Dec 13, 2022)

At least 10 to 15 years. Wife wants to stay forever. I think it’s too big of a house for 2 people after the kids move out… I’m mid 40’s so probably until retirement.


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## EbS-P (Dec 13, 2022)

I think smart load center control will start being more widely adopted.  Will that mean your 100 amp service will be adequate in the dead of winter while baking, running heatpump and charging a car?    They are marketing it like it should.  But it will take a new panel and at that point why not just upgrade to 200 amp service.   

Do it right the first time. And that probably means spending more than you think and being really skeptical about the lowest bid.   If you have space in the panel I think the resistive strips make sense.  

I’m looking at 8k$ to replace ductwork for 3000 sq ft.  Just ducts no equipment.  Like most things the duct work won’t last forever.  Getting properly sealed and insulated ducts might be consideration.   It might help up stairs and you could possibly, with single variable speed compressor set up two zone AC.


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## NoGoodAtScreenNames (Dec 13, 2022)

Yes the panel was upgraded when we went solar but we fitted it with 100 amp main breaker due to the supply line. The problem with 200 amps is that I have 150 foot underground service line going across 3 driveways in 1.5 inch conduit. It was going to be pretty pricey ($8K) when we looked into it with solar. So far I’ve gotten away with 100 amps with an inefficient AC along with all high efficiency electric appliances, a dual speed pool pump, a 16 amp level 2 car charger while also charging another car on a level 1. Future potential loads would be more / higher amped car chargers and electric resistance heat. But that’s hopefully a project for a future day / owner… But building it to fall over to resistant heat when I have the oil burner seems too much especially with an upgrade to 200.  I know oil isn’t great, but I’m using a high bio blend (50%) - and wood so my fossil fuel use is fairly low as it is.


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## EbS-P (Dec 13, 2022)

NoGoodAtScreenNames said:


> Yes the panel was upgraded when we went solar but we fitted it with 100 amp main breaker due to the supply line. The problem with 200 amps is that I have 150 foot underground service line going across 3 driveways in 1.5 inch conduit. It was going to be pretty pricey ($8K) when we looked into it with solar. So far I’ve gotten away with 100 amps with an inefficient AC along with all high efficiency electric appliances, a dual speed pool pump, a 16 amp level 2 car charger while also charging another car on a level 1. Future potential loads would be more / higher amped car chargers and electric resistance heat. But that’s hopefully a project for a future day / owner… But building it to fall over to resistant heat when I have the oil burner seems too much especially with an upgrade to 200.  I know oil isn’t great, but I’m using a high bio blend (50%) - and wood so my fossil fuel use is fairly low as it is.


I remember now….  100 amp makes sense to make it work.  I’d pull wire for 10kw strips. Breaker for what ever you choose.  Smart load management on an electric oven and car charger  and I don’t see why 100 amps isn’t plenty.  Check out Vue energy,  i heard a podcast where they were hyping this tech.   Domestic hot water off the boiler right?


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## EbS-P (Dec 13, 2022)

Back to the idea of bosh.  I feel I read somewhere that there were more problematic than others.  But I can’t remember where.  It’s a chunk of change and having this talk with hvac techs is probably beneficial.  I joined hvactalk.com  and they are helpful but don’t give any diy or pricing advice


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## NoGoodAtScreenNames (Dec 13, 2022)

EbS-P said:


> I remember now….  100 amp makes sense to make it work.  I’d pull wire for 10kw strips. Breaker for what ever you choose.  Smart load management on an electric oven and car charger  and I don’t see why 100 amps isn’t plenty.  Check out Vue energy,  i heard a podcast where they were hyping this tech.   Domestic hot water off the boiler right?


Used to have a dual system. One indirect off the oil and then a straight electric. That’s all gone now and I’m just one HPHW that steals waste heat in the air from the boiler. When we fixed the boiler we got rid of the unused coils that were the main source of the leaking.


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## pirates712 (Dec 13, 2022)

I haven't read through this whole thread, but I wanted to add that the ducted mitsubishi system we had put in over the summer has the option to turn off the blower during defrost. I have the electric strips locked out and I've never noticed when it defrosts. For 40f+ non-hyper heat would be fine.


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## NoGoodAtScreenNames (Dec 13, 2022)

I think I could get away with 100 amps forever once I get my Mr. Fusion plugged into my kitchen.


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## begreen (Dec 14, 2022)

EbS-P said:


> Like most things the duct work won’t last forever.


 Metal ductwork will certainly last a lifetime if done right. Most flex duct is a plastic film sandwich with insulation and a spring coil in between. It may not last forever, but plastic has a long lifespan if rodents don't get to it.


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## peakbagger (Dec 14, 2022)

I have had many experiences over the years with flex duct in commercial work. It is always getting crushed and yanked on. I used to see the "spaghetti monster" concepts where they was one rectangular box on the discharge of the unit and then multiple duct connections all over the box with long runs of flex duct run to the drops. If they were balanced at all, it was when it was brand new. On occasion we would find a duct completely disconnected. Inevitably the returns would be short circuiting. The contractor that installed these systems at the mill I worked for got paid to maintain the equipment so they really didnt care if the systems needed a lot fo call in work to maintain them.


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## EbS-P (Dec 14, 2022)

begreen said:


> Metal ductwork will certainly last a lifetime if done right. Most flex duct is a plastic film sandwich with insulation and a spring coil in between. It may not last forever, but plastic has a long lifespan if rodents don't get to it.


I asked about all metal ducts.  Labor and extra material cost it’s cheaper to replace 2-3 times.  That’s probably the rest of my life.


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## begreen (Dec 14, 2022)

With a proper design, the ductwork should last the life of the house. It's infrastructure and not normally a replaced item.


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## woodgeek (Dec 14, 2022)

EbS-P said:


> I asked about all metal ducts.  Labor and extra material cost it’s cheaper to replace 2-3 times.  That’s probably the rest of my life.


I went with metal trunks, and insulated flex on the distribution points (its supposed to be quieter).

I assume it will last decades.


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## begreen (Dec 14, 2022)

woodgeek said:


> I went with metal trunks, and insulated flex on the distribution points (its supposed to be quieter).
> 
> I assume it will last decades.


That's how I went too, R8 flex on the branches. It's 16 yrs old now and will easily outlast me.


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## semipro (Dec 14, 2022)

I can attest that rigid duct is louder.  I removed poorly installed fiberboard and flex duct and replaced with all rigid duct except for the distribution box.  The noise at the registers was much louder.  Fortunately, I soon after replaced our air handler with a much quieter unit and all is well.  

I can also confirm that mice can really do a number on flex duct.


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## NoGoodAtScreenNames (Dec 19, 2022)

I’m having someone come out this week. I’ve been thinking about the options.

The downstairs is 4 rooms plus a bathroom - all pretty open (no doors and wide entryways). Air movement should be pretty easy. It works well when running the insert on the far end. Treating as one zone makes sense.  I’ve been thinking about an air handler in the basement to evenly distribute it, but I could also get away with a wall unit or two (though I don’t love the aesthetics). One way cheaper than the other?

Upstairs is harder, 3 bedrooms, 3 bathrooms (2 off bedrooms) an office and a small room leading to the attic entry.  Lots of closed doors which would point to an air handler, but also potentially a lot of unoccupied rooms, especially when kid(s) go off to college. Having multiple units would be nice, but access to an outside wall may be hard without running the lines in the front of the house for some rooms. I was thinking about ceiling cassettes with the refrigerant lines running in the attic, but that would require condensate pumps which can be noisy. If I close a door can I shut the vent to the room? 

Last thought is that since there are going to be two units they don’t necessarily have to be the same type and size. Hot air rises and cool air falls. Does it make sense for heat pump performance on the first floor and cooling on the second? But that’s probably over complicating things.


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## begreen (Dec 20, 2022)

31º outside and for yucks I tried our 2 stage heat pump out to see how it performs at this temp by raising the thermostat a degree. The verdict is, it works. The cycle lasted 20 minutes. The HP did not go into defrost mode. It's calm with no wind so that helped. Still, not bad for a 16 yr old system. Temps are expected to drop tomorrow night. Do I test the old system at 25º?  Maybe, if it's not too windy.


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## Highbeam (Dec 20, 2022)

begreen said:


> 31º outside and for yucks I tried our 2 stage heat pump out to see how it performs at this temp by raising the thermostat a degree. The verdict is, it works. The cycle lasted 20 minutes. The HP did not go into defrost mode. It's calm with no wind so that helped. Still, not bad for a 16 yr old system. Temps are expected to drop tomorrow night. Do I test the old system at 25º?  Maybe, if it's not too windy.



We’ll be into the mid teens tonight they say. Woodstove is running, loping along. It’s hard to stop burning wood even to just test the heat pump system but that’s the only way to know what it can do.


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## NoGoodAtScreenNames (Dec 21, 2022)

The quote I received for $40k earlier in the thread was for two 3 ton Carrier Infinity units. My insert is rated at about 35k btus and does a fine job of maintaining the temperature in the house down into the 20s without the oil kicking on much if at all. That quote probably assumed on a 0 degree day after a power outage that I would want it to raise the temperature from 45F to 70F in short order. Having a heat pump that can maintain temps at lower outdoor temps is different than one that can raise the indoor temp in those same temps. I’m hoping I can find a cheaper quote focused on maintaining temps as a secondary to the oil.


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## maple1 (Dec 21, 2022)

That's a crazy price.  Did it include all new duct work and maybe a panel/entrance upgrade?


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## woodgeek (Dec 21, 2022)

NoGoodAtScreenNames said:


> The quote I received for $40k earlier in the thread was for two 3 ton Carrier Infinity units. My insert is rated at about 35k btus and does a fine job of maintaining the temperature in the house down into the 20s without the oil kicking on much if at all. That quote probably assumed on a 0 degree day after a power outage that I would want it to raise the temperature from 45F to 70F in short order. Having a heat pump that can maintain temps at lower outdoor temps is different than one that can raise the indoor temp in those same temps. I’m hoping I can find a cheaper quote focused on maintaining temps as a secondary to the oil.


Sounds about right to me.  They were hoping for a big score.

I could carry my 2250 sq ft house on a single 4 ton Carrier Infinity unit FTR, down to 10°F or so.


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## EbS-P (Dec 21, 2022)

begreen said:


> 31º outside and for yucks I tried our 2 stage heat pump out to see how it performs at this temp by raising the thermostat a degree. The verdict is, it works. The cycle lasted 20 minutes. The HP did not go into defrost mode. It's calm with no wind so that helped. Still, not bad for a 16 yr old system. Temps are expected to drop tomorrow night. Do I test the old system at 25º?  Maybe, if it's not too windy.


From 32 down to 17 my unit does not lose capacity.  Defrost certainly depends on the humidity.  When my heat strips kick on is where I paid a lot $$ not to feel cold air for a few minutes.   



NoGoodAtScreenNames said:


> The quote I received for $40k earlier in the thread was for two 3 ton Carrier Infinity units. My insert is rated at about 35k btus and does a fine job of maintaining the temperature in the house down into the 20s without the oil kicking on much if at all. That quote probably assumed on a 0 degree day after a power outage that I would want it to raise the temperature from 45F to 70F in short order. Having a heat pump that can maintain temps at lower outdoor temps is different than one that can raise the indoor temp in those same temps. I’m hoping I can find a cheaper quote focused on maintaining temps as a secondary to the oil.


Is two systems necessary or a luxury.  I decided that it was a luxury I didn’t need and with a wood burner on each floor I don’t need my heatpump to keep up on the coldest days.  

I’m considering adding a mini split to for the extra capacity.  Here a MR cool unit would be fine.


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## NoGoodAtScreenNames (Dec 21, 2022)

Nope. They would adjust the ducting in the basement to just service the first floor and new ducting in the attic. Panel would have been ok, but did not include a new service line to the house. That was another $8k on top of the $40k. Needless to say I did not take them up on that and this thread lives on…


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## EbS-P (Dec 21, 2022)

NoGoodAtScreenNames said:


> Nope. They would adjust the ducting in the basement to just service the first floor and new ducting in the attic. Panel would have been ok, but did not include a new service line to the house. That was another $8k on top of the $40k. Needless to say I did not take them up on that and this thread lives on…


Well I have approached it from the “what’s the bare minimum that you could get by with”   If you don’t know ask.  And then ask if the tech has a heat pump.  And what they would install at their house. Butchers don’t eat filet and prime rib.  Remember they are half salesmen half tradesmen. 

Can it be done in stages?   Attic ducts are less than ideal. Have you thought about attic encapsulation?  

Don’t do anything until you get a room by room load calc code requires it but many won’t bother.  

Rest of my replay was lost due to bad connection but basically it said any heatpump system without backup heat is oversized and you probably waisted money on the oversized equipment.  Embrace backup heat will be required 7-10 days a year.  And during record/near record cold.  

Binned data existed that tells you the number of hours you can be expected to be below design temp and knowing the equipment and your heat load calculation can tell you with some certainty how much backup heat you need at certain temps.  Have not found it for free yet.  Any good hvac company will have this software.  Ask for it.  

Welcome to the HVAC rabbit hole.


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## NoGoodAtScreenNames (Dec 21, 2022)

EbS-P said:


> From 32 down to 17 my unit does not lose capacity.  Defrost certainly depends on the humidity.  When my heat strips kick on is where I paid a lot $$ not to feel cold air for a few minutes.
> 
> 
> Is two systems necessary or a luxury.  I decided that it was a luxury I didn’t need and with a wood burner on each floor I don’t need my heatpump to keep up on the coldest days.
> ...


For heating I don’t think it’s needed. For AC we probably do - at least for the humidity control. It’s pretty uncomfortable upstairs on a sticky summer day, even if the temps aren’t too high with the current central AC running continuously. The warmer humid air just floats above the colder air that pours back downstairs. Was also thinking about a single ceiling cassette in the hallway upstairs to help  if the central AC isn’t doing all it needs to for the second floor.


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## EbS-P (Dec 21, 2022)

NoGoodAtScreenNames said:


> For heating I don’t think it’s needed. For AC we probably do - at least for the humidity control. It’s pretty uncomfortable upstairs on a sticky summer day, even if the temps aren’t too high with the current central AC running continuously. The warmer humid air just floats above the colder air that pours back downstairs. Was also thinking about a single ceiling cassette in the hallway upstairs to help  if the central AC isn’t doing all it needs to for the second floor.


Separate humidity  from temperature.  Is it too hot or hot and humid.   If you don’t have numbers it’s hard to make a good decision.  I cool 2000 sq ft up stairs and 1000 down with a 3 ton unit.  So 6 cooling tons has to be oversized.   Do you currently have an upstairs air return I forget?


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## NoGoodAtScreenNames (Dec 21, 2022)

Too humid mostly. It can be very uncomfortable and be only 75F on an overcast day. We have returns upstairs, not including the stairs, but everything is on the floor. Nothing to pull down the hot air.


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## begreen (Dec 21, 2022)

Highbeam said:


> We’ll be into the mid teens tonight they say. Woodstove is running, loping along. It’s hard to stop burning wood even to just test the heat pump system but that’s the only way to know what it can do.


True. And the woodstove is not stopping in these temps. But I can measure duct outlet temp to see what kind of heat it's putting out.


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## EbS-P (Dec 21, 2022)

NoGoodAtScreenNames said:


> Too humid mostly. It can be very uncomfortable and be only 75F on an overcast day. We have returns upstairs, not including the stairs, but everything is on the floor. Nothing to pull down the hot air.


I have decided to install a whole house dehumidifier.  Not saying that it’s a good fit for you but it’s an option


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## woodgeek (Dec 21, 2022)

EbS-P said:


> I have decided to install a whole house dehumidifier.  Not saying that it’s a good fit for you but it’s an option


Really?  Before you see the result of airsealing?


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## EbS-P (Dec 21, 2022)

woodgeek said:


> Really?  Before you see the result of airsealing?


Yep…  we don’t run ac for at least 3-4 months when the humidity is really high.  Plus it’s going to be ducted to the crawl space too for 50-100cfm of dry ventilation

Edit… and it will take some latent load off the acc upping its sensible capacity.  That with a bit more insulation I’m hopeful I can keep the 3 ton unit run for another decade.


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## NoGoodAtScreenNames (Dec 21, 2022)

Met with someone today. Brainstormed a lot of different options on zoning both with and without a separate unit in the attic. Don’t have a quote yet but the starting point is going to be a whole house central AC / heat pump with existing ducts. For upstairs we’d do a mini split running off the same outdoor unit in the ceiling in the hallway. If doors are closed they still get the benefit of the ductwork. If open they would get better airflow from the upstairs split if needed. It’s a bit of an overlap in the zones but he thought it’d work pretty well. 

We would do a non-hyper heat Mitsubishi since we have the backup wood / oil and it will  be easier on the 100 amp issue.  Really cold weather here is really just January and February. Otherwise it’s highs in the mid 30s and night time lows in the 20s. But the oil and wood can deal with the heat pump not running on cold nights. This seems the least complicated / most likely to succeed / hopefully most cost effective method than the other quotes. Cautiously optimistic. 

And yes - they will do all the heat load calcs. They handle the rebating for the utility which requires an outside design review before signing off on the rebate and starting the work.


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## EbS-P (Dec 21, 2022)

NoGoodAtScreenNames said:


> Met with someone today. Brainstormed a lot of different options on zoning both with and without a separate unit in the attic. Don’t have a quote yet but the starting point is going to be a whole house central AC / heat pump with existing ducts. For upstairs we’d do a mini split running off the same outdoor unit in the ceiling in the hallway. If doors are closed they still get the benefit of the ductwork. If open they would get better airflow from the upstairs split if needed. It’s a bit of an overlap in the zones but he thought it’d work pretty well.
> 
> We would do a non-hyper heat Mitsubishi since we have the backup wood / oil and it will  be easier on the 100 amp issue.  Really cold weather here is really just January and February. Otherwise it’s highs in the mid 30s and night time lows in the 20s. But the oil and wood can deal with the heat pump not running on cold nights. This seems the least complicated / most likely to succeed / hopefully most cost effective method than the other quotes. Cautiously optimistic.
> 
> And yes - they will do all the heat load calcs. They handle the rebating for the utility which requires an outside design review before signing off on the rebate and starting the work.


Not knowing any details that seems like a better solution than two units to my novice brain.


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## begreen (Dec 21, 2022)

Highbeam said:


> We’ll be into the mid teens tonight they say. Woodstove is running, loping along. It’s hard to stop burning wood even to just test the heat pump system but that’s the only way to know what it can do.


OK, 24º outside. I ran the heat pump test again. Indoor room temp at 71º. The ducted air test read 81.4º or about 10º above ambient. That's better than I expected. It's still pulling heat from the cold outside air. At 45º outdoor temp we get about 108º air coming from the same duct. Then, just for yucks I switched over to the resistance heaters for comparison and got 95.7º air.

The wood stove is at 350º and ready for a reload but it's irrelevant in this test because I am not checking the change in room ambient temp.


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## Highbeam (Dec 22, 2022)

begreen said:


> OK, 24º outside. I ran the heat pump test again. Indoor room temp at 71º. The ducted air test read 81.4º or about 10º above ambient. That's better than I expected. It's still pulling heat from the cold outside air. At 45º outdoor temp we get about 108º air coming from the same duct. Then, just for yucks I switched over to the resistance heaters for comparison and got 95.7º air.
> 
> The wood stove is at 350º and ready for a reload but it's irrelevant in this test because I am not checking the change in room ambient temp.


So you’re not interested in the ability of the heat pump to heat your home but in its ability to make “some” heat rise in a duct? Did you think it would fail to make any heat at a particular temperature?

The test I would consider to gain a data point is to let the stove go cold and the heat pump take over at certain ambient conditions. Just don’t want to let the stove go cold when we’re all home for Christmas break.


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## EbS-P (Dec 22, 2022)

It’s 62 outside now.   Hod both stoves running yesterday afternoon.  Basement is now 64 upstairs 68. Last load upstairs was 9pm last night.  Both stoves could have been fired once today but I won’t.  Heatpump cop will be 4.6 or higher all day.  And if my outside coil is be low 58 degrees I’ll be getting some latent heat and probably won’t get out of first stage.  

But the deep freeze is coming.  We will be below design temp for considerable amount of time and my uninsulated crawlspace and leaky and uninsulated parts of the return duct means anything below 25 I can’t maintain temp.


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## EbS-P (Dec 22, 2022)

NoGoodAtScreenNames said:


> Met with someone today. Brainstormed a lot of different options on zoning both with and without a separate unit in the attic. Don’t have a quote yet but the starting point is going to be a whole house central AC / heat pump with existing ducts. For upstairs we’d do a mini split running off the same outdoor unit in the ceiling in the hallway. If doors are closed they still get the benefit of the ductwork. If open they would get better airflow from the upstairs split if needed. It’s a bit of an overlap in the zones but he thought it’d work pretty well.
> 
> We would do a non-hyper heat Mitsubishi since we have the backup wood / oil and it will  be easier on the 100 amp issue.  Really cold weather here is really just January and February. Otherwise it’s highs in the mid 30s and night time lows in the 20s. But the oil and wood can deal with the heat pump not running on cold nights. This seems the least complicated / most likely to succeed / hopefully most cost effective method than the other quotes. Cautiously optimistic.
> 
> And yes - they will do all the heat load calcs. They handle the rebating for the utility which requires an outside design review before signing off on the rebate and starting the work.


The more I think about this the more I wonder if adding extra cooling upstairs really solves the problem or is it just a bandaid?  Are you cooling downstairs below the set point to keep 

The issue is hot air rises and there is not enough mixing to keep the upstairs close to the the downstairs set point.    Assuming you are well air sealed the next point of attack would be keeping sun out of south  and west windows. 

 Window awnings or louvered overhangs really need to be more widely used.   

Next we need to really keep sun off the whole structure.  Deciduous trees/plants that don’t grow taller than two stories need to more widely used.   

Last thing to consider is how to keep hot air downstairs year round.


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## NoGoodAtScreenNames (Dec 22, 2022)

EbS-P said:


> The more I think about this the more I wonder if adding extra cooling upstairs really solves the problem or is it just a bandaid?  Are you cooling downstairs below the set point to keep
> 
> The issue is hot air rises and there is not enough mixing to keep the upstairs close to the the downstairs set point.    Assuming you are well air sealed the next point of attack would be keeping sun out of south  and west windows.
> 
> ...



The AC thermostat is downstairs so we have to set that lower in order to feel any relief upstairs. He thinks with the doors open the upstairs unit would be able to carry the load on it’s own pretty well, but if it gets a little assist from whatever is happening with the downstairs thermostat then so be it. I suppose we could test that by closing vents on the second floor. 

House faces slightly south east so most of the windows are shaded. Solar panels “shade” 75% of the SE facing roof. NW gets midday through afternoon sun in the summer. The attic stays cool though. We leave windows open on both ends and I put in the foil radiant barrier on the rafters. That’s not too common up north, and gets a few funny looks from people when they go up there, but it makes a big difference. The attic temp stays around 100F on a hot summer day below the barrier and in the 130s above.


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## woodgeek (Dec 22, 2022)

NoGoodAtScreenNames said:


> The AC thermostat is downstairs so we have to set that lower in order to feel any relief upstairs. He thinks with the doors open the upstairs unit would be able to carry the load on it’s own pretty well, but if it gets a little assist from whatever is happening with the downstairs thermostat then so be it. I suppose we could test that by closing vents on the second floor.
> 
> House faces slightly south east so most of the windows are shaded. Solar panels “shade” 75% of the SE facing roof. NW gets midday through afternoon sun in the summer. The attic stays cool though. We leave windows open on both ends and I put in the foil radiant barrier on the rafters. That’s not too common up north, and gets a few funny looks from people when they go up there, but it makes a big difference. The attic temp stays around 100F on a hot summer day below the barrier and in the 130s above.


And if the attic floor is properly airsealed and insulated, it could be 150°F up there and it wouldn't leak a significant amount of heat to the house.


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## NoGoodAtScreenNames (Dec 22, 2022)

woodgeek said:


> And if the attic floor is properly airsealed and insulated, it could be 150°F up there and it wouldn't leak a significant amount of heat to the house.


Yeah - I did a full air sealing and R49 insulation. The only real weak spot is the door to the stairs. I don’t think heat gets pushed down as much as cool air is sucked up and is replaced in the living area by humid outside air. I’ve thought about changing from a closet door to a try exterior door but haven’t got around to it - and maybe outside my diy capabilities.


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