In heating mode the outdoor coil becomes the evaporator, pulling heat from cold outdoor air or the ground, and the indoor coil becomes the condenser. Air-source units lose capacity as it gets colder, so they are backed by electric strips or a furnace below the balance point; cold-climate inverter units keep working well below freezing. Ground-source units use buried loops for steadier source temperatures.
Heat pump's running on strips all day at 35 outside, it should be carrying that load on its own, check the charge.
If a heat pump blows air that feels cool at 90 degrees, explain it before the customer calls it broken: skin is warmer than that.
Also heard as
- HP
Related terms
Reversing valve
The four-way valve in a heat pump that swaps which coil gets hot discharge gas, switching between heating and cooling.
Defrost
A cycle that melts frost off a heat pump's outdoor coil or a refrigerated evaporator so it can keep moving heat.
HSPF
Heating seasonal performance factor: a heat pump's seasonal heating output in Btu divided by its electricity use in watt-hours.
COP
Coefficient of performance: heat moved or delivered for each unit of energy put in, with both measured in the same units.
Dirty sock syndrome
A musty, sweaty-sock odor blown out by an air conditioner or heat pump, caused by microbial growth on the indoor coil.