I see most of the people in the comments here have older model heat pumps.

Newer model heat pumps are quite a bit better than even ones made 10 years ago.

My dad had one put in two years ago for his garage kitchen, and it's worked quite well, even in fairly cold temperatures. Most importantly, that heat pump doesn't have an auxiliary mode, and yet it still works in sub freezing temperatures.

It would work even better if it were ground source, but those are both expensive and require digging up the yard.

I have a heat pump heating and cooling my basement in Atlantic Canada.

Temperatures in the winter hold steady around -20C with some dips a few times in the -40c range when accounting for windchill.

Works just fine. I keep my basement a nice 21C. Heating works well. I see lots of disinfo posted online about heat pumps not working in the cold and it’s all horseshit. Make sure you’re buying a heat pump that’s built for colder temperatures and you’re golden.

The main thing with heat pumps is that they obviously do heating and cooling. For most other systems, those two functions are separate, and can be sized appropriately.

If you live in a climate that is mostly hot, with some cold days, you'd size to accommodate the hottest days. If you live in a cool/cold climate, where you'd only occasionally need cooling, you'd size for the coldest days. Going oversize is bad because it is inefficient and just doesn't work as well. It is often better to size the system to accommodate 99% (or whatever %) of days, and have a little backup heat and/or cooling capability for when the pump can't keep up than it is to oversize and run inefficiently most days.

I lived in an apartment with a heatpump sized to handle the cold, and it kept me warm always with no trouble. It wasn't that cold of an environment, though. During the summer, it would kick on to cool the place, and it would cool very fast. That sounds good, but what happened is the temperature would be fine, but the humidity would be very high, and I would get condensation on my windows and mildew in my closets. I ended up having to increase the hysteresis of the system, so instead of letting the temperature rise a couple degrees above the set point and cooling a couple degrees below the set point, it had to swing much further. That made the system run long enough in one shot to decrease the humidity, but it basically made it so I'd have to either let the place get uncomfortably hot first, or cool it down to uncomfortably cool.

If the system were smaller, maybe there would be a few days a year where I would have to wear a sweater inside, but I wouldn't have to worry about 150 days of too much humidity.

The last thing to think about is air-source vs ground-source. Air source is basically a drop in for an air conditioner, but has a lower limit on temperature it will operate. That limit has gotten a lot lower over the years, but AFAIK, there are theoretical limits it can't beat, depending on the physics of the system and particular refrigerant. Ground source, aka geothermal, should work most places provided you have the space for it, and money to install it. Underground never gets cold enough that the physics of heat pumps aren't effective.

What do you consider cold? I have one in central Ohio. It was my primary winter heat source until I had gas installed a few years back. Now the price of gas is so cheap I don't run the heat pump in the winter. Obviously still use it for AC in the summer.

Define cold.

I have an air-water heat pump as the only source of heat and hot water in my house. It takes heat from the air outside and dumps it into a 200 litre water tank. I'd guesstimate that 80% of the homes in my neighborhood have the same setup.

Temperatures are going to be around -10°C for the next few days. When the silver falls below -15°C a resistive element kicks in to help the pump. In my climate I won't see more than a handful of those per year.

Nordic models scale down to -30°C before doing the same.

The cold-climate ones start to struggle at around -20C, for reference. (Not the windchill, that's an imaginary number)

If that doesn't regularly happen where you live, you're fine.

Newer heat pumps are awesome. Northeast USA, with EcoEr brand. Two winters now close to single digits but rarely below freezing and it works like a charm. Mine is rated to operate to -40f. They had to wire it up for single heat source mode, by default they were wired for secondary heat source on the older models. Humidifier module can be added for winter comfort, my neighbor has that. Not sure what the cost tradeoff vs gas is, but it is definitely way cheaper than oil, which is what we replaced. What I like the most about it is that I can wave my two middle fingers at the oil industry and say hello to solar energy.

Summer cooling feels like Arctic cold, and comes with built in dehumidifier for comfort. It definitely works harder to heat in winter than cooling in the summer.

There are mini splits which require less construction, lower cost, with good cooling, but winter heat operating temp stops near 30f.

There's lots of options out there depending on where you live , budget, needs.

Good luck !

Look up the model number. There are some that maintain 100% capacity down to negative temps, and there are some that lose capacity as the temperature outside drops. You can look up something called a “submittal data sheet” to find out the output capacity at different temperatures.

Capacity is measured in BTUs. So, if the heat pump is a 30,000 BTU model and it’s 47 degrees outside, it may produce 30,000 BTUs. However, at 17 degrees outside, it may only produce 20,000 BTUs. At -5 F, it may only do 10,000 BTU. Other models will keep 30,000 BTUs all the way down to -15F. The trade off is they use more electricity. Checking the data sheet can help you figure out what your model is capable of.

Mitsubishi is generally regarded as the best brand and they sell a line called “hyper heat.” These maintain capacity in low temps. Other brands have similar.

Technology connections has two videos about heat pumps from the perspective of someone in a relatively cold climate https://youtu.be/7J52mDjZzto https://youtu.be/43XKfuptnik

Lived in a house that had a heat pump with resistive electric heat as a backup in Canada. Never noticed a significant difference between that and other houses I’ve lived in that had natural gas furnaces.

Aux heat would kick whenever it was below about -5°C. That house would be about 20 years old now and had decent insulation for the location and age. It never really felt like the furnace struggled to keep the house warm, or was running all the time.

Cost wise it didn’t seem significantly better or worse than natural gas. It was definitely using more juice in the winter when there was a cold snap, but it wasn’t crazy amounts. The electric bill was actually highest in the summer when the heat pump was cooling.

Yes, Massachusetts. I have a dual fuel heat pump with natural gas backup installed in 2020, so it's a newer system. And I have one heat pump mini split in the least energy efficient, but most used room in my house (large, high ceilings, exterior walls on three sides, and a skylight).

The first couple of years I noticed when it got just below freezing, the central heat pump seemed to struggle to keep up. Then this year I replaced my windows and got new wall insulation in both of the main bedrooms and bathrooms (previous insulation was original from the 1960s and shredded to bits with huge gaps.)

After those improvements, I've been running my heat pump down to 20⁰F/-7⁰C so far without any issues at all. I'm excited to see how cold we can get and this system still keep up. I am still supplementing my one large room with the mini split, but that's mostly because all my plants are in here, so I keep this room warmer than 68⁰F/20⁰C.

I got one put in my 1200sqft manufactured home 4 years ago. It was able to keep most of the house 68 degrees with it in the single digits without breaking the bank. It struggles the most with just above freezing and foggy. This is because it has to constantly defrost the outside unit.
Overall 10/10 compared to forced air electric heating.

Swede here, my parents use geothermal heating, my apartment has district heating.

my co-worker put one in a few years ago at their house out in the country, but they have multiple alternatives for heat when it's "too cold"; the original fuel oil furnace, a pellet stove, a wood fireplace, and electric on a ripple circuit. the heat pump alone would not be enough in this climate where -40 or colder is not uncommon.

I live in Ontario where we go down to -30C in the harshest conditions.

We have a heat pump and a furnace and they alternate based on efficiency

Somewhere around -5 to +5 C it switches from the heat pump to the furnace

I think you could get by a bit colder but it really loses out on efficiency vs burning gas unless you invest in a geothermal heat pump

Pretty cold (average low temps are below freezing 5 months of the years - lowest about 30 below, though that was before the heat pumps).

Two logs houses - the heat pumps have done a great job, though we still use the wood stoves some (often just for the coziness/nostalgia).

I live in the Nordics and my house is prrimarily heated by a geothermal heat pump. The temperature here has been between -20C and -30C for the last week, the pump can easily keep the room temperatures at +19C until the outside temperatures drop under -25C, after that the electric resistor kicks in to provide assistance.

The secondary heat source is the giant baking oven, which i heat every other day if gets this cold. The fully heated oven alone raises the room temperatures by 5-6C, which helps a lot to take the load of the heating pump and keeps the electric bill smaller.

I have been planning to install air/air-water heat pumps to both floors, they would be a good backup during these cold spells and would also provide cooling during the summer. And if I install a smart control system, I can have the air units do extra heating/cooling automatically when the electricity is cheap.

I just haven't had the time to do the research where it would be best to install them and the prices rose steeply after Russia attacked Ukraine. So I'll wait for a while before I'll get those.

Yes, and they work great. A good quality one goes to -20 C or even lower

I had one when I lived in Maryland, it worked well. It kept the apartment warm and doubled as an air conditioner in the summer. I had always heard growing up that they never made it warm enough but that was not my experience.

I have heat pumps in some rooms (mainly for cooling) in the lower Hudson Valley, New York. Mine aren’t effective at heating the house when temperatures fall below 50 F. But my house is almost 100 years old and extremely drafty, so it may not be the best point of comparison.

If temps are going to be below 30F regularly, you'll need an auxiliary source. My parents got one last year, if they don't switch off it'll run constantly to keep temps at ~55F and drive their electric bill through the roof. It works well for them during the day in the winter most of the time and during the fall and spring.

PA isn't the coldest, but I lived in two different places in PA that had heat pumps. I never had an issue in either place. They were awesome.