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

[NoGoodAtScreenNames]

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!

 

[EbS-P]

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

 

[NoGoodAtScreenNames]

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.

 

[EbS-P]

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.

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

 

[begreen]

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?

 

[woodgeek]

"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?

 

[NoGoodAtScreenNames]

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.

 

[Highbeam]

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

 

[EbS-P]

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?

 

[peakbagger]

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.

 

[NoGoodAtScreenNames]

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...

 

[maple1]

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.

 

[woodgeek]

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.

 

[EbS-P]

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.

 

[stoveliker]

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 ..

 

[semipro]

@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:

1. Can be configured as either a 2 or 3 ton system.
2. Heats at very low ambient outdoor temps (in our case, no backup electric heat strip needed. We have wood stoves anyway)
3. Very quiet outdoor unit, compact, can be wall-mounted.
4. Variable-speed inverter compressor
5. 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.
6. 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

 

[begreen]

1. 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.
2. 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.

 

[velvetfoot]

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?

 

[maple1]

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

 

[NoGoodAtScreenNames]

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?

 

[maple1]

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).

 

[semipro]

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.

 

[EbS-P]

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.

 

[NoGoodAtScreenNames]

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.

 

[clancey]

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