Conversation

@skylar

Depends on type. I have water-water, and a long tube in the ground. That isn't dependent on air temperature, but more costly to install.

Air ones will depend on humidity, as the condensor fins will frost up and need regular de-icing cycles.
Where I live, they become uneconomical around 0 degrees Celsius, compared to district heating. (i.e. efficiency drops below 2x)

@tyler @thatguyoverthere