[WorldMaker]

The strength of your heat pump shouldn't be outside surface temperature, but underground aquifer temperature. Those two temperatures are related but not as directly as they seem. A good aquifer in certain cavernous regions of the US might stay about 55 degF year round, regardless of outside surface temperature. 55 degF is still below what a lot of people want their home to be year round so a heat pump still has to supplement heat somehow in winters (or radiators or what have you), but a "free" boost to 55 degF is still a better starting place than 20 or 40 degF outside temperature.

I don't think latitude is a factor in how efficient a heat pump you can find, I think the type geography under you feet is (probably where "interior" regions probably have more luck than coastal regions), combined with how well regulated or unregulated your area's aquifer generally is (things like nearby wells and industrial water dumping will effect aquifer levels and temperatures). (Maybe not enough heat pump proponents realize that you only have good, cheap heat pumps if you have a powerful EPA and other Water protection groups fighting the good fight in your region.)

[estimator7292]

You're talking about geothermal heat pumps which are far less common than air-to-air heat pumps because they are far more expensive.

These are entirely disjoint concepts.

[cwillu]

Nit: disjoint product classes, but clearly related concepts.

[glxxyz]

The prices when I looked weren't that different- it was about C$30k Canadian for air source and C$40k for ground source (which I went with).

[theluketaylor]

30K would be on the higher end for air source. My install this year was 25k CDN including a lot of duct work.

40K is also on the low end for geothermal. I'm guessing you were able to trench instead of drill?

If you can afford ground source it's by far the best option in cold climates. Steady ground heat means you get the same efficiency all year round. The install can be eye-watering though.

[glxxyz]

Yes horizontal loop, 200 metre trench ~2m deep with 6 pipes at the bottom. Took 3 days for a 20 ton excavator to dig and fill in the trench. Maybe I got lucky with the installer but it wasn't eyewatering. Vertical loops do cost a lot more. Repairing the lawn with turf or professional landscaping would have cost more than the install, so I did it myself with a tractor, some spare topsoil, and a few bags of Costco grass seed.