@corbet Similar results here, although we don't have the same low temperature range that you do. We put a lot of $$$ and effort into ensuring the house was extremely well-insulated and airtight (with an ERV for fresh air) before doing it, as ti was clear that the energy delivery capability of the heat pumps would be far lower than the natural gas boiler we had previously.
Of course all of that work would have reduced gas consumption too, but the boiler didn't give us cooler air in the summer and the heat pumps do 🙂
@corbet what's the type? Air-to-water? We've got an air-to-water one and it worked flawlessly in -15C (5F). And the service guy told us that they successfully tested it in -32C (-26F). But insulation is key. What also matters greatly is the temperature of heating water, the higher the lower the COP is.
@corbet @sesivany the problem with air source is that the energy requirements scale with delta t squared, meaning you have way more difficulty surviving extremes. With ground source they scale with delta t.
I did a ground source from air source conversion a couple of years ago and the energy savings are impressive (of course, so too were the federal tax credits at that time).
@corbet By air-to-water I meant air as the source and water as the heating medium. We have the same type then. It's sufficient here. We only have 2 weeks of such freezing weather a year. Our annual energy balance is 8.5 MWh produced and 9.6 MWh consumed. A deficit of 1.1 MWh is great for a house that is completely on electricity.
@corbet The unspoken downside is that many of the 'frigoriste" techs that repair these are scammy and that's if it was even installed properly (eg: proper vacuum on lines) so that it doesn't leak in five years. One service call and all your savings are lost.
@corbet What's the mechanism for banking electricity from summer to winter?