How Heat Pumps Work

How does a heat pump heat and cool a home?

A heat pump is one all-electric system that both heats and cools by moving heat rather than burning fuel. In summer it pulls heat out of your home like an air conditioner; in winter it reverses and pulls heat from outdoor air into your home, efficient comfort for many St. Louis-area houses.

Reviewed by Matthew Palmieri, President Updated July 13, 2026

The simple version

A heat pump uses refrigerant and a reversing valve to move heat in either direction. Instead of burning gas to make heat, it moves heat, which is why one outdoor unit can cool in summer and heat in winter.

Interactive diagram

One machine, both seasons

Cooling mode: heat is absorbed indoors and released outdoors.

Hot refrigerant / warm airCold refrigerant / cool air

Tap or click a numbered marker to see what each part does, or watch the animated flow to follow the cycle.

Cooling mode

In summer, a heat pump works like a central air conditioner (see also how central air works): it absorbs heat from inside your home and releases it outdoors, leaving cooler, drier air behind, critical in humid St. Louis summers.

Heating mode

In winter, the reversing valve flips the cycle. Even cold outdoor air contains heat energy; the heat pump extracts it and moves it inside. No combustion flame in the heat-pump-only path.

Defrost and “cold air” moments

Outdoor coils can frost in winter. Heat pumps run brief defrost cycles to clear ice; you may notice temporary cooler supply air or steam at the outdoor unit. That's normal operation, not necessarily a failure. Persistent ice, error codes, or no heat still need service.

Do heat pumps work in Missouri winters?

Yes, today's cold-climate heat pumps perform far better in freezing weather than older generations. For our coldest stretches, many homeowners choose dual-fuel (hybrid): heat-pump efficiency most of the year, gas furnace power when temperatures plunge. Compare dual-fuel vs. heat-pump-only.

Efficiency ratings

Heat pumps are rated by SEER2 (cooling) and HSPF2 (heating), higher generally means more efficient. Variable-speed equipment can improve comfort and humidity control; see single-stage vs. two-stage vs. variable-speed. Efficient upgrades may qualify for Ameren rebates and federal credits.

Repair vs. replace

Heat pumps often last about 12 to 15 years with good care. Major compressor or refrigerant issues on an aging unit may favor replacement. Use repair or replace, compare heat pump vs. furnace, or request a free second opinion.

Efficiency and operating costs depend on your specific equipment, home, and local utility rates. We'll model the real numbers for your home during a free in-home estimate.

Frequently asked

Do heat pumps work when it's below freezing?

Yes. Modern cold-climate heat pumps are engineered to deliver useful heat well below freezing, far better than older models. For the coldest Missouri snaps, many homeowners choose a dual-fuel (hybrid) system that automatically switches to a gas furnace when temperatures drop.

Is a heat pump cheaper to run than a furnace?

It depends on your local electricity and gas rates, home insulation, and equipment. Because a heat pump moves heat instead of burning fuel, it can be very efficient, but operating cost isn't universal. We compare options for your house instead of quoting a one-size savings number.

What is a dual-fuel or hybrid heat pump system?

It pairs an electric heat pump with a gas furnace. The heat pump handles cooling and most heating; when it gets very cold, the system switches to the furnace. Details are in our dual-fuel explainer.