Heat pump power requirements 1650 sq ft home

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Old 12-11-13, 08:28 AM
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Heat pump power requirements 1650 sq ft home

I'm building a new home, the main floor is 1650 sq ft, and the basement will be finished with a rec room, utility room, bathroom, storage room, and laundry room. I got 2 quotes from places telling me a 3.5 ton will be fine with 15 kW aux heater. The place I am going with says a 5 ton is what will be better with a 20 kW aux heater. First of all with the 5 ton work on 200 amp service. Will also be electric range, dishwasher, electric dryer. No other electric heat. Second, if not I would like to stay with a 200 amp service, so will the 3.5 ton do the job, and I'll go with baseboard heaters in the basement for the occasional use of the rec room. 400 amp service is out of the question. Thanks for any help!
 
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Old 12-11-13, 10:15 AM
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where in Canada are you located - how cold does it get ? If you're in Victoria, 3.5 ton would be good - if Moosonee, maybe 5 ton would be needed if a heat pump would work at all.

I have a similar house, near Boston - I have a 3.5 ton unit with 20kw auxiliary heat on 200 amp service. I wish it was a 4 ton when temperatures are below 32F (0C) though.
I find that I do need 20kw for those times when the temperatures are in the low 20Fs (-8C say) and under or when the snow is wet requiring frequent defrosts and especially when I switch to Emergency Heat.

Your new house will probably be well insulated - maybe you should get a heat loss calculation / load line done to guide the heating requirements.

If your temperatures often go below 10F (~-12C ) you might even consider 25kw backup.
The size of the electrical service is determined more by the size of the auxiliary heaters then the heat pump proper. For example, my 20 kw heaters draw about 85 amps , whereas the heat pump is more like 4kw or around 16 amps - and even with stove and dryer running never any issues with capacity. One would expect the heat pump vendor to have the kw demands of the components readily available. It is als important to decide on the size of the auxiliary heaters so that the electrician can install the appropriate size wiring.
 

Last edited by dsomerv; 12-11-13 at 10:50 AM.
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Old 12-11-13, 11:03 AM
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I'm in Grand Falls Newfoundland. From the local vendors, they say typically 10 days a year is all the aux heating coil is used, I think it will be more. I'm also doing a propane insert in the living room on the main floor for those 10 days in Jan and Feb it gets cold, it's rated for 1600 sq ft also. I would rather go bigger and not need it than smaller and wish I went bigger. If I could go 5 ton/20kW aux on 200 amp panel I would. Everyone I talk to says I "can" but will it pass the electrical inspection...I'm not sure and don't want to risk it. If the 3.5 ton/15 kW aux will keep the house warm, and I have to use the propane on cold days that's fine with me too.
 
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Old 12-12-13, 08:37 AM
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So your winter temperatures in Newfoundland run around freezing - colder at night. Still, I'd be surprised if the AUX heat only came on 10 days a year. The Boston climate is not much different but I use AUX for weeks when we get a cold spell - this is mostly due to my slightly undersized heat pump .

I agree that the 5 ton / 20kw scheme would probably be more comfortable - and if it's a reasonable air handler you will be able to switch off 10kw of the 20kw AUX heat except when it gets real cold or Emergency Heat is needed for some (hopefully rare) reason.

I agree with others you've talked with that 200 amp panel should be just fine. The 5ton unit would probably be on a 40 amp circuit - even though it would typically run at maybe 25 amps.
So 85 amps max for AUX heaters, 25 amps for heat pump fits comfortably with 200 amp service.

If you're concerned about inspection, maybe you should just show the electrical wiring plans / loads to the building dept / inspector for tentative approval before the install.



The other issue with the 5ton unit is the AirConditioning ... if you would be using it with the full 5 tons cooling it might cool the house to fast to remove humidity ... but I'd expect that the heat pump would have two or more speeds so that AC could be running at 2 or 3 ton rate (say) - worth checking out , although maybe you don't have AC requirements anyway.
 
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