How Do Heat Pumps Work? A Plain-English Guide

A heat pump heats your home by moving heat instead of making it. Even when it’s cold outside, the outdoor air still holds heat energy. A heat pump uses refrigerant to absorb that heat outdoors, concentrate it with a compressor, and release it inside your home. In summer, it runs the same process in reverse and works as an air conditioner. Because it moves heat rather than burning fuel to create it, a heat pump can deliver more heat energy than the electricity it uses. Here’s how it works, step by step, in plain English.

The basic idea: moving heat, not making it

A furnace creates heat by burning natural gas or propane, or by running electric heating elements. A heat pump works more like your refrigerator. Your fridge pulls heat out of the inside compartment and dumps it into your kitchen, which is why the back of it feels warm. A heat pump does the same thing on a larger scale, pulling heat from the outdoor air and moving it into your house.

That’s the key to why heat pumps are so efficient. Moving heat takes much less energy than generating it from scratch.

How a heat pump heats your home, step by step

1. Absorbing heat outdoors. Cold liquid refrigerant flows through the coil in the outdoor unit. Even on a cold day, the outdoor air is warmer than that refrigerant, so the refrigerant absorbs heat and turns into a gas.
2. Compressing it. The compressor squeezes that gas, which raises its temperature well above the temperature you want inside your home.
3. Releasing heat indoors. The hot refrigerant travels to the indoor coil in your air handler. The blower pushes your home’s air across that coil, the air picks up the heat, and warm air flows out of your vents.
4. Starting over. Having given up its heat, the refrigerant turns back into a liquid, passes through an expansion valve that drops its pressure and temperature, and heads back outside to absorb more heat.

How it switches to cooling

A heat pump has a part called a reversing valve that changes the direction the refrigerant flows. In cooling mode, the indoor coil absorbs heat from your home and the outdoor unit releases it outside, exactly like a central air conditioner. One system handles both seasons, which is why heat pumps are so popular across Arkansas, Oklahoma, Missouri, and Texas.

Why heat pumps are so efficient

Because a heat pump moves existing heat instead of generating it by burning fuel, it can deliver two to three times more heat energy than the electricity it consumes in moderate weather. Electric resistance heat, like baseboard heaters or heat strips, converts electricity into heat one-for-one. That difference is why a heat pump can lower heating costs compared with all-electric resistance heat.

Heating efficiency is rated by HSPF2, and cooling efficiency by SEER2. Higher numbers mean more heating or cooling for each unit of electricity.

What happens when it gets really cold?

As outdoor temperatures drop, there’s less heat in the air to capture, so a heat pump has to work harder and its output falls. Most systems handle this in two ways.

Auxiliary heat

On the coldest days, electric heat strips inside the air handler kick in to help. That’s what it means when your thermostat shows “AUX heat.” It’s normal in cold weather, but if it’s running constantly on a mild day, something may be wrong. Read more about what AUX heat on your thermostat means and how heat strips work.

Dual-fuel systems

Some homes pair a heat pump with a gas furnace. The heat pump handles most of the season, and the furnace takes over when it gets very cold. Learn how dual-fuel heat pumps work.

Today’s cold-climate heat pumps keep working efficiently at much lower temperatures than older models. For more on winter performance, see how cold weather affects heat pumps.

Why your heat pump sometimes looks like it’s steaming

In cold, damp weather, frost can build up on the outdoor coil. To clear it, the heat pump briefly runs a defrost cycle, switching into cooling mode for a few minutes to warm the outdoor coil. You may see steam rising from the unit and hear a whoosh when it switches back. That’s normal. A unit that stays coated in thick ice for hours is not, and it needs service.

The parts of a heat pump system

• Outdoor unit: the coil, compressor, fan, and reversing valve.
• Indoor unit: an air handler with a coil, blower, and often backup heat strips. In dual-fuel systems, it’s a furnace instead.
• Refrigerant lines: copper lines connecting indoor and outdoor units.
• Thermostat: a heat pump thermostat that controls heating, cooling, and auxiliary heat. Here’s why the right heat pump thermostat matters.

Types of heat pumps

All heat pumps work on the same principle of moving heat, but they pull that heat from different sources.

Air-source heat pumps

The most common type in homes. An air-source heat pump extracts heat from the outside air in winter and transfers heat from your home to the outside air in summer. It connects to your ductwork through an indoor air handler, just like a central air conditioner. For most homes, this is the heat pump people mean when they say “heat pump.”

Ductless mini-split heat pumps

A ductless system pairs an outdoor unit with one or more wall-mounted indoor units, with no ductwork required. Mini-splits are a great fit for additions, garages, sunrooms, and older homes without ducts, and each indoor unit controls its own zone.

Geothermal (ground-source) heat pumps

A geothermal heat pump extracts heat from the ground instead of the air. A few feet below the surface, the ground stays at a fairly steady temperature year-round, so a ground-source system doesn’t lose performance on freezing days the way an air-source unit can. Water circulates through buried loops to absorb heat in winter and release it in summer. Geothermal systems cost more to install but are among the most efficient heating and cooling technology available. Learn more about geothermal heating.

Water-source heat pumps

Less common in homes, a water-source heat pump uses a well, pond, or water loop as its heat source. You’ll see these more often in commercial buildings.

Heat pump water heaters

The same technology can heat water. A heat pump water heater pulls heat from the surrounding air to warm the water in its tank, using far less electricity than a standard electric water heater. Here’s how a heat pump water heater compares with a conventional one.

How much energy does a heat pump use?

Heat pump efficiency is often described by its coefficient of performance, or COP. A COP of 3 means the heat pump delivers three units of heat energy for every one unit of electricity it uses. Electric resistance heat has a COP of 1. That’s where the energy savings come from: the electricity runs the compressor and fans, while the heat itself comes from outside, essentially for free.

COP changes with the weather. On a mild fall day, a heat pump can run at very high efficiency. As outdoor temperatures drop toward freezing and below, there’s less heat to extract, the compressor works harder, and efficiency falls, although a modern heat pump still generally outperforms electric resistance heat.

Variable-speed, or inverter, heat pumps take efficiency further. Instead of switching fully on and off, the compressor ramps its speed up and down to match the load, which reduces energy use, keeps temperatures steadier, and improves comfort.

Pros and cons of heat pumps

Advantages

• One system for heating and cooling. A single heat pump replaces both a furnace and an air conditioner in many homes.
• Lower energy use. Moving heat takes less energy than generating it, which can reduce heating costs compared with electric resistance heat.
• No combustion. There’s no fuel burning in your home, so there’s no carbon monoxide risk from the heat pump itself.
• Even, comfortable heat. Heat pumps deliver steady, gentle warmth rather than blasts of very hot air.
• Better humidity control in summer. Especially with variable-speed models.

Disadvantages

• Performance drops in extreme cold. Air-source heat pumps rely on backup heat on the coldest days.
• Supply air feels cooler. Heat pump air is warm but not as hot as a gas furnace’s, which some homeowners notice at first.
• Year-round wear. Because it heats and cools, the system runs more hours per year than an air conditioner alone.
• Higher upfront cost for some types. Especially geothermal systems.

How long does a heat pump last?

With regular maintenance, most air-source heat pumps last roughly 10 to 15 years. Because they run in both heating and cooling mode, they accumulate operating hours faster than an air conditioner that only runs in summer. Geothermal ground loops can last decades, while the indoor heat pump unit typically lasts about 20 years. Annual service, clean filters, and a clear outdoor unit are the biggest factors in reaching the upper end of those ranges.

Sizing matters

A heat pump that’s too small will lean on backup heat all winter and struggle in summer. One that’s too large will short cycle, waste energy, and leave the home clammy in cooling mode. The right size comes from a load calculation that accounts for your home’s insulation, windows, ductwork, and local climate, not just its square footage.

Signs your heat pump needs service

• It’s blowing cool air in heating mode for long stretches.
• AUX heat runs constantly, even when it isn’t very cold outside.
• The outdoor unit is covered in thick ice that doesn’t clear after a defrost cycle.
• It short cycles, turning on and off every few minutes.
• You hear grinding, squealing, or loud buzzing from the outdoor unit.
• Your energy bills jump without a change in how you use the system.

Heat pump or furnace: which is right for you?

A heat pump is a strong choice if you want one system for heating and cooling, if your home doesn’t have natural gas, or if you want to cut your reliance on fossil fuels. A furnace, or a dual-fuel setup, may make sense if you have natural gas available and see long stretches of very cold weather. The right answer depends on your home, your fuel options, and how you use your system, and it starts with a proper load calculation.

Heat pump vs. gas furnace at a glance

How to get the most from a heat pump in winter

A few habits make a big difference in comfort and energy use during heating season.

• Avoid big thermostat setbacks. Dropping the temperature several degrees overnight and then cranking it back up in the morning can trigger auxiliary heat, which uses much more electricity. Small, steady adjustments work better with a heat pump.
• Use a thermostat designed for heat pumps. Smart and programmable heat pump thermostats manage recovery gradually so the system doesn’t lean on backup heat.
• Keep the outdoor unit clear. Leaves, snow, and ice around the unit restrict airflow and hurt performance. Make sure water from the roof doesn’t drip directly onto the unit and freeze.
• Change the filter. Restricted airflow makes the system work harder in both heating and cooling mode.
• Don’t cover the unit. A heat pump runs all winter, so it needs to breathe. Covers made for air conditioners aren’t meant for heat pumps.

What’s included in heat pump maintenance

A professional heat pump tune-up before winter typically includes checking the refrigerant charge, testing the reversing valve and defrost controls, inspecting electrical connections and the capacitor, cleaning the indoor and outdoor coils, checking the auxiliary heat strips, measuring airflow, and confirming the thermostat is controlling the system correctly. Catching small problems in the fall is far better than discovering them on the first freezing night. Schedule heating maintenance to get your system ready for the season.

Keep your heat pump running efficiently

Because a heat pump works year-round, it racks up roughly twice the running hours of an air conditioner. That makes regular maintenance even more important. Change your filter on schedule, keep the outdoor unit clear of leaves and snow, and schedule a tune-up before heating season. Paschal’s Planned Protection Membership includes up to two system checks a year. For heating service, repair, or a new system, explore our heating services or schedule heating repair online.

Frequently Asked Questions

How does a heat pump work in the winter?

A heat pump absorbs heat from the outdoor air, even when it’s cold, using refrigerant. The compressor concentrates that heat, and the indoor coil releases it into your home. On very cold days, auxiliary heat strips or a gas furnace can help.

Does a heat pump work in cold weather?

Yes. Output drops as temperatures fall, but modern heat pumps keep heating well into freezing temperatures, and cold-climate models work at much lower temperatures. Backup heat covers the coldest days.

Is a heat pump cheaper to run than a furnace?

Compared with electric resistance heat, a heat pump is usually much cheaper to run because it moves heat instead of generating it. Compared with a gas furnace, it depends on local electricity and gas rates and your climate.

Why is steam coming out of my heat pump?

That’s usually the defrost cycle. The heat pump briefly reverses to melt frost off the outdoor coil, which can produce steam. It’s normal. Thick ice that doesn’t clear needs service.

Can a heat pump heat and cool my home?

Yes. A reversing valve changes the direction refrigerant flows, so the same system heats in winter and cools in summer.

At what temperature does a heat pump stop working?

A heat pump doesn’t suddenly stop, but its heating output and efficiency drop as the temperature falls. Many standard models start relying more on backup heat somewhere below freezing, while cold-climate models keep heating efficiently at much lower temperatures.

What are the disadvantages of a heat pump?

Air-source heat pumps lose performance in extreme cold and may need backup heat, the supply air feels cooler than a gas furnace’s, and the system runs year-round, so it accumulates more wear. Geothermal systems also have a higher upfront cost.

How long do heat pumps last?

Most air-source heat pumps last about 10 to 15 years with regular maintenance. Geothermal indoor units often last around 20 years, and their ground loops can last decades.