A heat pump is heating and cooling equipment that moves heat from one place to another using a refrigerant cycle, instead of making heat by burning fuel. In winter it pulls heat from outdoor air, the ground or water and releases it indoors; in summer it reverses and works like an air conditioner. Because it moves heat rather than generating it, an electric heat pump is generally considered a more environmentally friendly alternative to gas-fired equipment.
How a heat pump works
- In the evaporator coil, cold liquid refrigerant absorbs heat from the source (outdoor air, ground or water) and boils into a gas.
- The compressor squeezes the gas, raising its pressure and temperature.
- In the condenser coil, the hot gas gives up its heat to the indoor air or water and condenses back to liquid.
- An expansion valve drops the pressure and the cycle repeats.
A reversing valve swaps the roles of the indoor and outdoor coils, switching between heating and cooling. Efficiency is described by the coefficient of performance (COP): the heat delivered divided by the electricity used. In normal operation a heat pump’s COP is above 1, meaning it delivers more heat than a resistance heater using the same electricity.
Types of heat pumps
| Type | Heat source | Typical use |
|---|---|---|
| Air-source (ducted or ductless mini-split) | Outdoor air | Houses, townhomes, apartments, small commercial |
| Ground-source (geothermal) | Ground loops or wells | Homes and buildings with land for loops; very stable efficiency |
| Water-source (WSHP) | A building water loop | Offices and multi-unit buildings with a boiler and cooling tower on the loop |
| Air-to-water | Outdoor air, heating water | Radiant floors, radiators, domestic hot water |
| VRF | Outdoor air (or water) | Commercial buildings with many zones |
Cold climates and backup heat
An air-source heat pump’s capacity and efficiency fall as the outdoor temperature drops. Cold-climate models extend the range, but many systems in Canada and the northern US still include backup heat, such as electric strips or a gas furnace (a dual-fuel system). Outdoor units also run defrost cycles in winter.
Site and installation tips
- Size equipment from a proper heat loss and gain calculation, not by rule of thumb.
- Mount outdoor units above snow level with clearance for airflow, and plan drainage for defrost meltwater.
- Refrigerant piping, pressure testing and evacuation should be done by licensed technicians to the manufacturer’s instructions.
- Check noise limits near property lines and bedroom windows.
Related terms
- Fan Coil Unit (FCU)
- Air Handling Unit (AHU)
- Variable Frequency Drive (VFD)
- Ductwork
Related templates and guides
- Introduction to Mechanical and Electrical Systems
- Five Ways to Make Your Building More Efficient
- HVAC Design Quality Checklist
Frequently asked questions
Do heat pumps work in cold climates?
Yes, but output and efficiency drop as it gets colder. Cold-climate air-source models are designed to keep heating at much lower temperatures than older units, and ground-source systems are not affected by air temperature. In very cold regions, designers usually still provide backup heat.
What is the difference between a heat pump and an air conditioner?
Both use the same refrigerant cycle to move heat. An air conditioner only moves heat out of the building. A heat pump has a reversing valve, so it can also move heat into the building in winter, giving heating and cooling from one system.
Is a heat pump better than a furnace?
It depends on climate, energy prices and the building. A heat pump moves heat very efficiently and provides cooling too, while a furnace burns fuel to make heat. In cold regions, dual-fuel systems pair a heat pump with a furnace that takes over in the coldest weather.
Will a heat pump lower my electric bill?
Compared with electric baseboard or other resistance heating, usually yes, because it delivers more heat per unit of electricity. Compared with gas heating, the electric bill goes up while the gas bill drops, so overall savings depend on local energy rates.
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