Thermal
Heat Pump
Equipment that moves heat rather than generating it, using a refrigerant cycle that can run in either direction. A single machine for heating and cooling, and not a combustion appliance.
In more detail
A heat pump moves heat rather than creating it. A refrigerant circuit evaporates refrigerant at low pressure to absorb heat in one place and condenses it at high pressure to release heat in another; a reversing valve swaps the two, so one machine both heats and cools.
Because it moves rather than generates, output can exceed input. A coefficient of performance of 3 means three units of heat delivered per unit of electricity, which is why heat pumps are compared on COP, HSPF2, SEER2 and EER2 rather than on a combustion efficiency percentage. Performance is temperature-dependent: capacity and COP fall as outdoor temperature drops for an air-source unit, which is why rated capacity is always quoted at a stated outdoor condition and cold-climate units are specified against a design temperature. Ground-source systems exchange with soil, whose temperature is far more stable.
Distribution is a separate question from the source. The same heat pump can feed ducted air handlers, ductless heads, or water for a hydronic system. And a heat pump is not a combustion appliance: no flame, no flue, no combustion byproducts in the house.
Why it matters
For most new houses the heat pump decision determines whether combustion equipment is in the building at all, which changes the air quality and safety picture as much as the energy one. It also changes what comfort feels like: heat pumps deliver lower supply air temperatures for longer periods than a furnace, which is more even in practice and reads as underwhelming to anyone expecting hot air at a register.
The common misunderstanding
That heat pumps do not work in cold climates. Capacity does fall as outdoor temperature drops, and older equipment struggled — but cold-climate units are rated at low outdoor temperatures and are in ordinary service in genuinely cold regions. What matters is whether a specific model's rated capacity at the local design temperature meets the calculated load, which is a number on a submittal rather than a general claim.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.