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.
Talk me into (or out of) a whole house heat pump to replace dead oil boiler
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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.
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.
maple1
Minister of Fire
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.
EbS-P
Minister of Fire
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.
I’m considering adding a mini split to for the extra capacity. Here a MR cool unit would be fine.
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…
EbS-P
Minister of Fire
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.
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.
EbS-P
Minister of Fire
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?
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.
EbS-P
Minister of Fire
I have decided to install a whole house dehumidifier. Not saying that it’s a good fit for you but it’s an option
EbS-P
Minister of Fire
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.
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.
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.
EbS-P
Minister of Fire
Not knowing any details that seems like a better solution than two units to my novice brain.
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
Minister of Fire
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.
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.
EbS-P
Minister of Fire
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.
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.
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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