How Heat Pumps Work and When They Make Sense

Heat pumps have moved from a niche technology to a mainstream option for heating and cooling homes. The idea behind them can seem counterintuitive at first: they warm a house in winter by pulling heat out of cold outdoor air or the ground. Once the principle clicks, it becomes easier to see why they can be efficient and when they are a good fit.

Moving heat instead of making it

A traditional furnace or boiler creates heat by burning fuel, and an electric heater creates it by passing current through a resistant element. A heat pump does something different. It uses electricity to move heat from one place to another.

The same principle runs your refrigerator. A fridge pulls heat out of its interior and releases it through coils at the back, which is why the back of a fridge feels warm. A heat pump does this on a larger scale, pulling heat from outside and releasing it inside your home. In summer, many heat pumps reverse the process and act as air conditioners.

Because moving heat takes less energy than generating it, a heat pump can deliver more heat energy to your home than the electrical energy it consumes. That ratio is the source of its efficiency.

The refrigeration cycle, simplified

Inside a heat pump, a special fluid called a refrigerant circulates through a closed loop. The cycle goes roughly like this:

1. The refrigerant passes through an outdoor coil, where it absorbs heat from the surrounding air or ground. Even cold air contains some heat, and the refrigerant is colder still, so heat flows into it.
2. A compressor squeezes the refrigerant, which raises its temperature significantly.
3. The hot refrigerant flows through an indoor coil, releasing heat into the home’s air or water.
4. The refrigerant passes through an expansion valve, cooling down again, and returns outside to repeat the cycle.

Types of heat pumps

Air-source

Air-source heat pumps draw heat from outdoor air. They are the most common type because they are relatively straightforward to install. Some deliver heat through ducts as warm air; others, called air-to-water systems, heat water for radiators or underfloor heating.

Ductless mini-split

A ductless system connects an outdoor unit to one or more indoor units mounted on walls or ceilings. It is useful in homes without ductwork or for heating individual rooms or extensions.

Ground-source

Ground-source, or geothermal, heat pumps draw heat from the ground through buried pipes. Below a certain depth, ground temperature stays relatively stable year-round, which can make these systems very efficient. Installation involves excavation or drilling, so upfront costs and disruption are higher, and space or ground conditions may limit where they are possible.

How they handle cold weather

A common question is whether heat pumps work in cold climates. Efficiency does drop as outdoor temperatures fall, because there is less heat in the air to collect. Modern cold-climate models, however, are designed to keep working in very low temperatures. Some systems include a backup heat source for the coldest days, either electric resistance or an existing furnace or boiler.

In cold weather, an air-source unit will also run defrost cycles periodically to clear frost from the outdoor coil. This is normal and usually brief.

What helps a heat pump perform well

Heat pumps tend to work best under certain conditions:

• A well-insulated home. Heat pumps usually deliver heat at a lower, steadier temperature than a boiler, so a home that holds heat well makes a real difference.
• Proper sizing. A system that is too small will struggle in cold weather, and one that is too large may cycle on and off inefficiently. A professional heat loss calculation helps get this right.
• Suitable heat emitters. For air-to-water systems, larger radiators or underfloor heating often work better than small radiators designed for very hot water.
• Good installation. Placement of the outdoor unit, refrigerant charge and controls all affect performance.

Running a heat pump differently

Living with a heat pump can involve some changes in habit. Many work best when left running steadily at a consistent temperature, rather than being turned off and then pushed to heat a cold house quickly. The air from vents may feel less hot than from a furnace, even though the room reaches the same temperature. Smart thermostats and the system’s own controls can help balance comfort and efficiency.

Costs and incentives

Installation costs vary with the type of system, the size of the home, existing ductwork or radiators, and whether electrical upgrades are needed. Running costs depend on local electricity and fuel prices and on the system’s efficiency in your climate. In some regions, government or utility programmes offer incentives toward installation. These change over time, so check what is currently available.

When a heat pump may make sense

A heat pump is often worth considering if:

• Your existing heating or cooling system is near the end of its life.
• You want one system for both heating and cooling.
• You do not have access to a gas supply, or want to move away from fossil fuels.
• Your home is reasonably well insulated, or you are planning insulation upgrades.

Getting quotes

Because performance depends so much on design and installation, it is worth getting more than one assessment from qualified installers. A good installer will look at your home’s insulation, calculate heat loss room by room, explain how the system will handle the coldest days in your area and discuss what changes, if any, your radiators or ducts might need.