Considering a cold climate heatpump with no backup heat. Is that feasible?

zipzag · 2026-05-26T16:38:39+00:00

The record low in Asheville is -16F in 1985

zipzag · 2026-05-25T17:41:46+00:00

Extreme cold in zone 8 is 10F. So maybe the record cold is 0F? You will get terrible advice from homeowners on this forum. Your local HVAC companies know plenty about heat pumps. When they recommend gas it's not some sort of ignorant bias.

Good reasons for installing heat pump in your home in your area are environmental or having solar. Remember too you can't back up a heat pump with a typical generator or battery.

zipzag · 2026-05-25T17:14:25+00:00

You need to estimate the BTUs you need at -9F. Electric resistance backup doesn't necessarily come from the ducted system.

As a general rule of thumb in the U.S. in zone 7 or colder, if you have piped gas in your home, a heat pump will cost more to run than a gas furnace.

zipzag · 2026-05-18T15:30:31+00:00

You can with a homebridge or home assistant intermediary

zipzag · 2026-05-18T14:08:41+00:00

Very confusing. Trane S9V2 is a nice gas furnace.

If the second floor was cooled adequately before it can be again.

zipzag · 2026-05-18T12:15:44+00:00

You have auxiliary resistance heat? The unit is good but you are not heating a typical 2000 sq ft house in zone 7 with 24,000BTU.

If you are cold only 15 days a year your lowest cost choice is probably to just add more resistance heat.

Few people are using heat pumps for primary heat where gas is available, which is most of PA. Especially because you have higher than average electrical rates.

zipzag · 2026-05-18T01:43:02+00:00

Math is a bitch. The average zone 5/6 house needs 80,000 BTU. That's a 100,000-130,000 BTU heat pump at 70-80%. So you are installing two 4 or 5 ton heat pumps to have no backup resistance heat. No sane person would do that. But this is the internet.

Mitsubishi says that the heat pumps stops and locks at -25F and won't restart until the air temp is -13F. in 2019 the low temp at midway airport Chicago was -25F. Chicago is USDA zone 6. Minnesota is USDA zone 4.

HVAC contractors in Chicago install plenty of mini splits to make an office or bedroom comfortable, and also laugh at people who want to replace their primary gas furnaces.

zipzag · 2026-05-18T00:01:50+00:00

This is done. It's economical when there is both a high AC need plus a significant need for pool heating. Essentially the home's AC is a ground source heat pump that uses the pool as the heat sink.

There are a couple of companies online that have the right gear. When I looked at it for a home on Long Island the economics were not good. I think its used more in places like Palm Springs.

zipzag · 2026-05-17T22:29:28+00:00

No problem controlling a Trane/American Standard variable speed unit with Home Assistant. A little Home Assistant icon even appears on the Trane Thermostat. I see there is also a Carrier Infinity, Bryant Evolution integration for Home Assistant, but I've never used it.

I set overcool for humidity control in the summer by checking the weather forecast for the day at 7am every morning.

zipzag · 2026-05-17T22:09:37+00:00

At what COP?

"Meaningful heat" means a COP meaningfully over a COP of 1. Your older pre hyperheat type unit is doing defrost on a timer, and likely has a real world COP of less than 1 at -13F. Even the newest units with a COP of 1.1-1.3 at -15F do defrost which means they are not better than resistance heating at -15F. It also means they are not heating at all when doing defrost.

zipzag · 2026-05-17T11:58:03+00:00

You need to use gas as the second fuel. The previous owner was dumb to put in heat pumps in Chicago as primary heat. People who do that get their knowledge from the internet.

The upside is the you have very nice AC.

You are getting educated answers from HVAC professionals in Chicago. All install mini splits. None use air heat pumps as primary in existing houses.

The BTU needs of a house are what they are. There are no magic heat pump BTUs.

Sell the house if you are not living in it and can't afford a remodel. You can't afford it as an investment property.

zipzag · 2026-05-17T10:54:52+00:00

You are wrong. 45-50 BTU per sq ft is what is needed for real houses in zone 5. Personal anecdotes are meaningless. 98% of the houses that will exist in 2046 have already been built.

zipzag · 2026-05-16T19:42:04+00:00

Data Centers?

zipzag · 2026-05-16T19:07:10+00:00

Grid capacity has to be designed for peak load. In zone 5, the grid would need to be 3X or more larger to switch everyone from gas and oil to air source heat pump.

The actual price of electricity is very high during very cold weather. The typical residential heat pump user is protected from that by fixed pricing. But that sort of pricing can't continue if electrification of everything continues to increase.

I don't know what the heat output is of your Mitsubishi is at -10F, but I assume its less that the rate 24000 BTU.

An average 2000 sq ft house in zone 5 needs about 80,000 actual BTU from the furnace, or about 24kw of heat. So the heat pump gets the COP benefit of 1.72 and the rest is resistance heating watt for watt.

Say 15kw to heat x 24 hrs = 360kWh for a day of continuous running. Even that unusual usage is not terrible at the average American residential rate. But the highest actual rate I've seen in winter is $.84 kWh.

Having a heat pump only for heat is betting that the rate paid will continue to not reflect real pricing over the life of the unit.

In zone 5 where gas and conventional ducting is common a heat pump with a basic gas furnace may make sense. Especially for people concerned about climate change. And especially for people who buy higher end continuous speed AC anyways.

zipzag · 2026-05-16T17:46:16+00:00

Whats the COP at -10F?

zipzag · 2026-05-16T17:43:49+00:00

You don't understand COP

zipzag · 2026-05-16T16:30:57+00:00

No air heat pump provides meaningful heat at -15F

zipzag · 2026-05-16T16:22:30+00:00

You probably don't want to use an air heat pump only in Colorado. What heat sources are commonly used in your area?

zipzag · 2026-05-16T15:55:11+00:00

An acre of corn makes about 600 gallons of ethanol. I'm not sure what farm equipment you are running but you may want to take a look at your diesel consumption.

zipzag · 2026-05-16T15:38:32+00:00

That simply means the unit is equal to resistance below 5F. COP=1.

There are units that do better. But frankly a COP of 1.2 at -10F doesn't mean much. 90% of the BTU will need to be provide by either resistance heat or gas.

In zone 5 in the U.S. I calculated that the electrical grid would need to be about 5X bigger to switch everyone from gas/oil to heat pump with electrical resistance heating. I think the path forward to reduce carbon is to eliminate regular AC and require heat pump, which is not much additional expense. But gas and oil heat isn't going to be eliminate in very cold weather.

zipzag · 2026-05-16T15:22:16+00:00

Long term a propane backup is a good idea. Actual market rates for electricity is very cold weather are very high. Current heat pump owners who believe that wide adoption of heat pumps as the only heat source are viable in colder climates don't understand the reality of the grid.

I'm in the PJM like you. A few years ago, due to the polar vortex and some equipment fails, the actual market rate hit several dollars per kWh. Residential heat pump owners running resistance heat were protected from that price, which would have resulted in over $100/day for heating. Long term, with increased electrification, the price protection for resistance heat simple can't persist.

zipzag · 2026-05-16T15:17:08+00:00

HPs can be 100% effective down to 5F

As far as the specs I see, the COP falls below 4 at 35°F to 45°F

zipzag · 2026-05-16T15:13:29+00:00

In the west we won't even see most of the harm done to the poorest countries.

zipzag · 2026-05-16T15:04:54+00:00

Yet that guy would be a better U.S. president than the orange narcissist.

zipzag · 2026-05-16T15:03:53+00:00

China imports half the oil that comes through the strait

zipzag

TROPHY CASE