How Does a Heat Pump Work?

A heat pump is one of the most efficient ways to heat and cool a home, but the name confuses people — it doesn't "pump heat" out of thin air by magic. The key idea is simple: a heat pump moves heat from one place to another instead of creating it. Your refrigerator already does this (it moves heat out of the food compartment); a heat pump does the same thing on a house-sized scale, and it can run in either direction.

Here's how it actually works, why one system can both heat and cool, and why it uses so much less energy than a furnace.

The big idea: move heat, don't make it

A furnace or an electric heater creates heat — by burning fuel or pushing electricity through a hot element. That's capped at 100% efficiency: you never get more heat than the energy you put in.

A heat pump relocates heat. Even cold winter air contains usable heat energy, and a heat pump collects that diffuse warmth, concentrates it, and delivers it indoors. Because the electricity only powers the moving — not the making — you get far more heat out than energy in. That's why a heat pump's efficiency (its COP, or coefficient of performance) runs 2.5 to 4.0: two and a half to four units of heat per unit of electricity.

The refrigerant cycle, step by step

A heat pump moves heat using a refrigerant — a fluid that boils and condenses at convenient temperatures — cycling through four stages:

1. Evaporator (absorb heat). Cold liquid refrigerant flows through the outdoor coil. Because it's colder than the outside air, heat flows into it, and the refrigerant boils into a low-pressure gas — carrying that heat with it.
2. Compressor (concentrate it). The compressor squeezes the gas, which raises its pressure and its temperature. Now the refrigerant is hot — hotter than your indoor air.
3. Condenser (release heat). The hot gas flows through the indoor coil. Because it's now hotter than the room, heat flows out into your home, and the refrigerant condenses back to a liquid.
4. Expansion valve (reset). The liquid passes through an expansion valve that drops its pressure and temperature sharply, making it cold again — ready to absorb more heat outside. The cycle repeats.

The clever part: heat naturally flows from hot to cold, and the compressor is what lets the system "borrow" heat from cold outdoor air and deliver it to a warmer house.

One system, both heating and cooling

The feature that makes a heat pump special is the reversing valve. It changes the direction the refrigerant flows:

• Heating mode (winter): absorb heat outside → release it inside.
• Cooling mode (summer): absorb heat inside → release it outside. This is exactly what an air conditioner does.

So a heat pump is an air conditioner that can also run backward. One outdoor unit, one indoor unit, both jobs. (More on that in heat pump vs air conditioner.)

What a heat pump looks like

From outside, an air-source heat pump looks almost identical to a central AC: a metal box with a fan beside the house. The difference is what it connects to indoors and that it runs in winter. There are a few common configurations:

• Ducted (central): the outdoor unit pairs with an indoor air handler that pushes heated or cooled air through your existing ducts.
• Ductless (mini-split): the outdoor unit connects to one or more wall- or ceiling-mounted indoor heads, no ducts needed. See what is a mini split.
• Ground-source (geothermal): instead of outdoor air, it draws heat from buried pipes in the ground, which stays a stable temperature year-round — the most efficient type, but the most expensive to install.

Why it saves energy and money

Because the COP is 2.5–4.0, a heat pump produces the same heat as electric resistance for a third to a half of the electricity. Against a furnace, the efficiency advantage is even larger on paper — the real dollar comparison then depends on local gas vs electricity prices, which we break down in heat pump vs furnace.

A heat pump's efficiency does drop as outdoor air gets colder (less heat to collect), which is why cold-climate models and backup heat matter — see do heat pumps work in cold weather.

Putting it to work for your home

If you're considering one, two numbers matter most: the size it needs to be (in BTU/tons) and what it will cost. Estimate the size with the heat pump sizing calculator, get an installed-cost range from the heat pump cost calculator or heat pump cost by state, and check the payback against your current heating with the heat pump payback calculator.

The bottom line

A heat pump works by moving heat rather than making it — a refrigerant cycle collects heat from outside, a compressor concentrates it, and it's released indoors, with a reversing valve letting the same system cool in summer. Because it relocates heat instead of creating it, it delivers 2.5–4× more heat than the energy it uses. That efficiency is the whole reason heat pumps are the fastest-growing way to heat and cool US homes. Keep going with the rest of our home-energy guides.