Air-source heat pumps for space heating and cooling.
A heat pump does not create heat, it moves it — which is why it delivers two to four units of heat per unit of electricity where a resistance heater delivers one. Running the cycle in reverse gives cooling from the same equipment.
Capacity falls as outdoor temperature drops, because there is less ambient heat available to move. Cold-climate models use variable-speed compressors and vapor injection to hold useful output well below freezing, but every unit has a balance point below which supplementary heat is needed. Size from the manufacturer's capacity table at your design temperature, not from the nameplate rating at 47°F.
Sizing too large is a real failure mode, not a safety margin: an oversized unit short-cycles, never reaches steady state, and dehumidifies poorly in cooling.
Stocked from Midea.
