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.
Talk me into (or out of) a whole house heat pump to replace dead oil boiler
- Thread starter NoGoodAtScreenNames
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
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.
$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.
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.
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.
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 $1k per ton plus whatever IRA incentives that may apply make it seem crazy to do just an AC.
I’m going to start talking to contractors again. I’m thinking that keeping an air handler in the basement for the first floor and blocking off the ducts to the second floor is best. Probably a new unit in the attic with either a single zone air handler or multiple heads. Multiple heads would be the preference I think if not cost prohibitive.
I’m still restricted to 100 amps but I’m hoping that avoiding resistive heat strips should leave me ok. Not sure everything can run on one outdoor unit that can ramp up / down to meet the demand of both floors or if it means two outdoor units. A lower amp option I guess would be preferable.
Any thoughts or advice before I start talking to folks again? Thanks everybody.
EbS-P
Minister of Fire
Advice.
1 avoid condensate pumps.
2 Heat pumps work really well in 40+ degree weather. I just was curious today and my 2009 unit runs a COP of 4 when it’s 52 degrees. So if you don’t need lots of cold weather capacity don’t spend extra for it.
3. Can contractor can install almost any unit but will they air balance it. I think by code they need to do a load calc. Ask for it. Pay 200$ 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.
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.
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.
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.
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.
EbS-P
Minister of Fire
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.
EbS-P
Minister of Fire
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.
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.
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.
EbS-P
Minister of Fire
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?
EbS-P
Minister of Fire
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
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.
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.
I think I could get away with 100 amps forever once I get my Mr. Fusion plugged into my kitchen.
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 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.
EbS-P
Minister of Fire
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.
With a proper design, the ductwork should last the life of the house. It's infrastructure and not normally a replaced item.
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.
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.
I can also confirm that mice can really do a number on flex duct.
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.
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.
Last edited:
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.
Similar threads
