What Types of Heat Pumps Are There?

Choosing among heat pumps starts with a simple question: where will the system collect heat? Air-source models draw energy from outdoor air, while ground-source systems use heat stored in the soil. Some designs exchange heat with a nearby water source. The name can sound technical, but the basic idea is practical: move heat rather than create it by burning fuel. The details matter.

There are also differences in how systems deliver warmth. Ducted units connect to existing air ducts; ductless models can serve individual rooms. Hybrid systems pair a heat pump with another heater, which may help in colder conditions. These categories can overlap, so labels alone do not reveal how a unit will perform in a particular home. A drafty house with old radiators presents different challenges from a well-insulated home with underfloor heating. Not every option fits.

This guide explains the main types of heat pumps, how they work, and what trade-offs homeowners may encounter. Climate, insulation, installation space, electricity costs, and the condition of existing equipment all affect the decision. Published efficiency figures are useful, but they do not guarantee identical results in every building. A qualified installer can assess the home, check equipment specifications, and estimate likely operating costs. Even then, estimates involve assumptions. Comparing options carefully—and asking what those assumptions mean—can make the choice clearer.

Table of Contents [Hide]

1 How Heat Pumps Are Classified by Their Heat Sources

2 Air-Source Heat Pumps and Their Main Variants

3 Ground-Source Heat Pumps: Geothermal and Ground-Loop Systems

4 Water-Source Heat Pumps and Their Operating Environments

5 Other Heat Pump Types for Specialized Applications

How Heat Pumps Are Classified by Their Heat Sources

What Types of Heat Pumps Are There?

Heat pumps are classified by where they collect heat: outdoor air, the ground, water, or indoor exhaust air. Air-source units draw energy from outside air and move it indoors. Air is everywhere. Their output can fall during very cold weather, so local winter temperatures matter. Ground-source systems use buried pipes to exchange heat with relatively stable soil temperatures. Water-source systems draw heat from a suitable lake, well, or other water body.

The U.S. Department of Energy reports that geothermal heat pumps can use 30%–60% less energy than conventional heating systems, though actual savings depend on the site and equipment. That range is useful, not a promise. Ground loops need space and careful installation; water-source designs also depend on reliable water access. Exhaust-air heat pumps recover warmth from ventilation air, often in tightly sealed buildings. Their performance depends partly on how much warm indoor air is available.

The International Energy Agency’s 2022 report, The Future of Heat Pumps, estimates that heat pumps supplied about 10% of global building heat demand in 2021. That figure covers different technologies and regions, so it does not predict one home’s results. Cold changes the picture. When comparing systems, check the heat source, winter design temperature, and available land or water. Classification helps, but real buildings rarely fit a perfect diagram.

What Types of Heat Pumps Are There? — How Heat Pumps Are Classified by Their Heat Sources

Heat-source type	Where the heat comes from	Common system configurations	Typical uses	Key benefits	Important considerations
Air-source	Outdoor air. The unit transfers heat between outdoor air and indoor air or a water-based heating system.	Air-to-air; air-to-water	Space heating and cooling; some systems can also heat domestic hot water.	Usually simpler to install than systems that require underground loops or a nearby water source; suitable for many building types.	Heating output and efficiency generally decrease as outdoor temperatures fall. Performance depends on climate, equipment design, and installation.
Ground-source (geothermal)	Heat stored in the ground, accessed through buried pipes known as ground loops.	Closed-loop horizontal or vertical systems; open-loop systems where local conditions and regulations permit.	Space heating and cooling, and sometimes domestic hot water, for homes and larger buildings.	Ground temperatures are generally more stable than outdoor air temperatures, which can support steady operation throughout the year.	Ground-loop installation can involve substantial excavation or drilling, site planning, and higher upfront costs.
Water-source	Heat from water, such as a lake, river, well, or a building’s water loop.	Closed-loop or open-loop arrangements, depending on the water source and system design.	Buildings with access to a suitable water body, well, or shared water-loop system.	Water can provide a relatively stable heat source when the supply is suitable and consistently available.	Feasibility depends on water availability, temperature, flow, water quality, permits, and environmental requirements.
Exhaust-air	Heat recovered from warm, used indoor air being removed by a ventilation system.	Ventilation heat-recovery heat pumps, often integrated with mechanical ventilation and hot-water systems.	Well-insulated buildings with mechanical ventilation and a steady supply of extract air.	Recovers some heat that would otherwise leave the building through ventilation.	The available heat is limited by the amount and temperature of exhaust air, so system capacity and building ventilation design matter.

Classification note: Air-source, ground-source, and water-source describe the main heat reservoirs. Exhaust-air heat pumps are a specialized type that recovers heat from ventilation air. Solar energy may supplement a heat-pump system, but solar-assisted systems are generally hybrid arrangements rather than a separate primary heat-source category.

Air-Source Heat Pumps and Their Main Variants

Air-source heat pumps transfer heat between outdoor air and a home. In heating mode, refrigerant absorbs heat outside and releases it indoors. The process reverses for cooling. Even chilly air contains usable heat, though efficiency generally falls as temperatures drop. Frost can collect on the outdoor coil, so the system periodically runs a defrost cycle. That detail matters.

Ducted models deliver conditioned air through ducts and can often use existing registers. Ductless mini-splits send heat directly to indoor wall or ceiling units, making room-by-room temperature control practical. A single outdoor unit can serve one indoor unit, or several. The latter setup needs careful sizing; uneven room loads can leave one space less comfortable.

Air-source systems also differ in compressor operation. Fixed-speed models switch on and off, while variable-speed models adjust output to match demand. Cold-climate versions may use enhanced compressors and controls to maintain heating performance in low temperatures. Some homes also need backup heat during severe cold. Not magic. Insulation, airflow, and installation quality still affect comfort and energy use. A technician should check the home’s heat loss, duct condition, and outdoor-unit location before recommending a configuration.

Ground-Source Heat Pumps: Geothermal and Ground-Loop Systems

Ground-source heat pumps, often called geothermal heat pumps, exchange heat with the soil or groundwater. They do not rely on deep volcanic heat. Instead, buried pipes use the ground’s relatively steady temperatures to help warm a building in winter and cool it in summer. No flames. A heat pump circulates fluid through the ground loop, then transfers heat indoors or outdoors as needed.

Most ground loops are closed systems. A water-and-antifreeze mixture circulates through sealed pipes without mixing with the soil. Horizontal loops sit in broad, shallow trenches, so they need enough open land. Vertical loops run through drilled boreholes and can suit smaller lots, though drilling adds cost. An open-loop system draws groundwater through the heat pump and returns or discharges it. Water quality, supply, and site conditions can make this option unsuitable.

Design matters as much as the equipment. Pipe depth, soil type, groundwater movement, and the building’s heating demand affect performance. A narrow yard may favor vertical drilling, but the added expense is real. Poorly sized loops can struggle during long periods of extreme weather. The trade-off is less tidy than a simple efficiency claim suggests: a ground-source system can use little outdoor space, yet installation may disturb the yard and require careful planning. I would not treat one layout as universally best.

Water-Source Heat Pumps and Their Operating Environments

Water-source heat pumps exchange heat with water rather than directly with outdoor air. The water may come from a pond, lake, river, groundwater well, or a dedicated closed loop. Water temperatures often change more slowly than air temperatures, which can help the system operate steadily through cold or hot weather. That matters. A pump beside a deep lake may face different conditions from one drawing shallow groundwater.

In a closed-loop design, sealed pipes carry fluid through the water, so the system does not continually draw water into the building. An open-loop setup does; it draws water through a heat exchanger and returns or discharges it. Water flow, quality, and seasonal levels all affect performance.

Sediment, minerals, or biological growth can foul equipment, so testing and maintenance are essential. The setting needs careful assessment. A small pond may not provide enough heat exchange, while a well must sustain the required flow. Designers should also consider changes to water temperature and local environmental requirements. It is tempting to treat a nearby water source as free heating and cooling, but that assumption can fail. Even a technically suitable site may need extensive piping, filtration, or monitoring.

Other Heat Pump Types for Specialized Applications

Specialized heat pumps solve problems that ordinary air-source systems may not. Ground-source systems exchange heat with soil or groundwater, where temperatures change less sharply than outdoor air. The U.S. Department of Energy’s Energy Saver reports that geothermal heat pumps can use 25–50% less electricity than conventional heating and cooling systems. That range depends on site conditions and equipment. A yard with shallow bedrock or limited drilling access can make installation difficult.

Absorption heat pumps use heat from natural gas, propane, solar-heated water, or waste heat rather than relying only on an electric compressor. They can suit facilities with steady waste heat or high heating demand. Heat-recovery heat pumps are another option: they capture warmth from refrigeration, exhaust air, or data-room cooling and redirect it to water or nearby spaces. The International Energy Agency’s 2022 report, The Future of Heat Pumps, notes that electric heat pumps can deliver three to five units of heat per unit of electricity. Specialized systems still need careful design. Sizing is easy to get wrong.

Tips: Ask for a site assessment before choosing a system. Check soil, water, and waste-heat availability. Compare measured seasonal performance, not just peak ratings. Even good plans miss details.