Heat pump

A device that uses work to move heat from a cooler source to a warmer space. Reversing its cycle can provide either heating or cooling.

Vapor-compression refrigeration: A refrigeration cycle that circulates a working fluid through compression, condensation, expansion, and evaporation. Most building heat pumps use this cycle to move heat between indoor and outdoor coils.
Air-source heat pump: A heat pump that exchanges heat with outdoor air. It is the most familiar building type, using outdoor air as its source or sink.
Heat: Energy transferred between systems because of a temperature difference. A heat pump transports this energy instead of creating all delivered warmth from electricity.
Furnace: A heating appliance that produces heat by burning fuel or using electrical resistance. Unlike a heat pump, a furnace generates heat rather than moving it from an external source.
Electrification: The replacement of direct fossil-fuel use with electricity across energy services and industries. Adopting heat pumps shifts building heating demand from fuels toward the electric grid.
Refrigerant: A working fluid that absorbs and releases heat as it changes pressure, temperature, or phase. Its changing state lets the heat pump absorb heat at one coil and release it at another.
Ground-source heat pump: A heat pump that exchanges heat with the ground through buried loops or wells. The ground's steadier temperatures can improve performance compared with outdoor-air exchange.
Work (thermodynamics): Energy transferred to or from a system by forces acting through a distance or other organized processes. Electrical work drives the compressor and enables heat to move against its natural direction.
Electric resistance heating: Heating that converts electrical energy directly into thermal energy through resistance. It provides a useful baseline: a heat pump can deliver more heat per unit of electricity.
Building decarbonization: The reduction or elimination of greenhouse-gas emissions from building construction and operation. Heat pumps can cut operational emissions when powered by sufficiently low-carbon electricity.

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