Last I read, which was years ago, was they still struggle under -20C. Which is not abnormal for many places in Canada. How do these perform in wicked cold times?

I have a heat pump and furnace combo. The heat pump works extremely well down to around -10C. Below that it takes a very long time to move the needle by half a degree. The furnace doesn’t kick in until the thermostat sees the house temperature trending in the opposite direction it’s attempting to achieve.

Unfortunately, its method of determining the time gradient of temperature is rather moronic and doesn’t take the temperature schedule into account. This means every morning when the schedule calls for higher daytime temperatures (even by just half a degree) the thermostat freaks out thinking that the house is cooling rapidly and kicks on the furnace to bring up the temperature.

This causes the system to needlessly run the furnace every single morning. It annoys the hell out of me but I don’t know what to do about it. Aftermarket thermostats aren’t very common around here (Canada).

they still struggle under -20C. Which is not abnormal for many places in Canada

Yes, but that’s why heat pumps in this country are typically paired with auxiliary electric heat. The heat pumps still contributes some amount, even at -30 or below, but the electric “tops up” the pre-warmed air that the heat pump makes.

And that is only really needed for a couple of months out of the year, even in places like Winnipeg or Edmonton.

20-30 years ago, the heat pump technology wasn’t as capable, and couldn’t do the job as well, but they have improves quite a lot since then.

Yes, but that’s why heat pumps in this country are typically paired with auxiliary electric heat.

Yes, and although it’s not very efficient to have auxiliary electrical heat, that’s a small percent of the overall year.

If you live in a home that hits -20C for 20 days per year, that’s really cold! But you’ll probably need the heater on for about 180 days per year at that point. Putting up with less efficiency for 20-30 days per year is still a net gain if the other 150 days of heating makes up for it.

I mean, a resistive electric heater is still (“just”) 100% efficient.

Yeah but if some direct combustion of a fossil fuel is cheaper than electricity, then the actual dollars per unit heat will be cheaper with a fossil fuel source.

Cheaper, but less efficient. Fossil fuels have a efficiency < 1.

Question is, what’s more important for you: money or environment…

Mine is rated for -25, which where i live in southern Ontario has been reached 3 times in 50 years (wind chill doesn’t count remember). And while I haven’t had a heat pump for one of those days I don’t think it would be a problem, after all the efficiency doesn’t just drop to 0, it just doesn’t work as well for that one day and my house could stay a safe level of warm for a day or 2 without heat anyway.

Despite this I am required to have an auxiliary heat source, so I get charged 30 dollars a month just for a gas hook up I haven’t used.

A lot of heat pumps have normal electrical heating as a backup as well.

I had a similar problem, fwiw I have an ecobee. I simply added an intermediary step an hour or two before the final temperature so the heatpump has a chance to go. There is also a threshold for auxiliary heat lock in the settings on the thermostat itself that doesn’t show up in the app which I increased which helped a lot.

I tried the intermediate step and even the minimum possible temperature increase of half a degree still triggers the bad behaviour. I can’t find any auxiliary heat lock setting. Maybe it’s in the service menu set by the HVAC installers? They set a password on that and won’t tell me what it is.