How Do Heat Pumps Work?
A heat pump moves heat using a refrigerant that evaporates and condenses as it circulates — the same cycle as a fridge or air conditioner, but reversible.
The refrigerant cycle, step by step
- Evaporator — cold liquid refrigerant absorbs heat from the outdoor air (even cold air contains heat) and boils into a gas.
- Compressor — compresses that gas, which raises its temperature sharply.
- Condenser — the hot gas releases its heat into your home and condenses back to a liquid.
- Expansion valve — the liquid expands and cools, and the cycle repeats.
Because the system is moving heat rather than creating it by combustion, it delivers far more heat energy than the electrical energy it consumes — a measure called COP (coefficient of performance), typically 2.5–4.
The reversing valve: heating and cooling
A reversing valve flips the direction of refrigerant flow. In summer the indoor coil absorbs heat (cooling your home) and dumps it outside — exactly like an AC. In winter the flow reverses, gathering outdoor heat and releasing it indoors.
What affects performance?
Efficiency drops as it gets colder outside (less heat to gather), which is why we calculate a balance point — the temperature below which backup heat is needed. Cold-climate models use enhanced compressors to maintain output well below freezing.
Types of heat pumps
The same refrigerant cycle powers every type — they differ in where they get and deliver heat:
- Air-source — exchanges heat with the outdoor air (ducted or ductless); the most common type.
- Ductless mini-split — air-source, but with wall/ceiling heads instead of ducts.
- Geothermal — exchanges heat with the stable ground instead of the air, for the highest efficiency.
- Dual-fuel (hybrid) — pairs a heat pump with a gas furnace that takes over on the coldest days.
Frequently asked questions
How does a heat pump work in simple terms?
It uses a refrigerant that evaporates and condenses as it circulates, moving heat from one place to another — pulling warmth from outside air (or the ground) into your home in winter, and reversing to cool in summer.
How does a heat pump heat without burning fuel?
It does not create heat — it moves existing heat. Even cold outdoor air contains heat energy, which the refrigerant absorbs and the compressor concentrates to a useful temperature indoors.
Do heat pumps work in winter?
Yes. Output drops as it gets colder, but cold-climate models keep heating efficiently well below 0°F. Below the balance point, backup heat assists.
Educational guide. Sources: US DOE / ENERGY STAR.