Types of heat pump

Types of heat pump

Heat pumps can come in many forms. The most common types are summarised as follows

Reversible air-conditioners / heat pumps  –      air-to-air

These are very widespread, especially in warmer climates. They can provide heating, but may not necessarily be the best appliance for ‘proper’ house heating.

Air Source heat pumps (ASHPs)            –            air-to-water

These are now a commonly used heating method. They extract heat from outside air and produce hot water for either underfloor heating or radiator circuits. They usually also heat a cylinder of domestic hot water (DHW).

Ground source heat pumps (GSHPs)     –    brine-to-water

Also more common now, these extract heat from the ground using either boreholes of horizontal trenches. They produce heated water in the same way as ASHPs. These are occasionally referred to as Geothermal. (Note, the term ‘brine’ is often used to describe any antifreeze).   Unlike the ASHP, this unit is usually installed in a utility room.

Water source heat pumps (WSHPs)             –       water-to-water

Water source systems extract heat from rivers, lakes or springs. Spring source can give excellent results, but are not very common.

Air source domestic hot water heaters (DHW)

These take the form of a hot water cylinder with a small air source heat pump on top.

Heat recovery

There are various applications where there is a ‘waste’ heat that is a little too cool for apparent use. Direct (passive) heat-exchange would be the first option, but heat pumps can have many uses here. ‘Waste’ heat from refrigeration is a form of heat recovery.

Heat distribution in the building (the heat emitter system)

Air-to-air systems can simply blow (recirculate) warmed air into a room. Larger systems may be ducted to various rooms. However, in Europe, the most common method of emitting heat is via warmed water that circulates in pipes to panel radiators or underfloor heating. ‘Emitters’ or ‘Heat emitters’ is a common term for either radiators or underfloor heating


Air-conditioning is the term commonly used for cooling. In some climates, the day-time air temperature can be above a comfortable level (e.g. say 23ºC or 74ºF). inside a building it can be considerably hotter; however, the overheating is often due to sunlight coming directly into the building. It make sense to stop overheating by shading (blinds etc.), and by reducing heat generation inside the building. Furthermore, the thermal-mass of a building (e.g. solid stone walls) can be used to advantage by absorbing daytime natural solar heat.

If the climate is simply too hot, there may be no option other than to use some sort of forced cooling. Blown air is the most common method; however, reducing the temperature of a stone floor can be a very effecting way of increasing comfort. Care is needed to avoid condensation.

Passive cooling

Water from a ground source system can be pumped directly around some underfloor heating system. This is sometimes called free-cooling, and is very cheap to run. Again, it must be designed well. It usually works best with boreholes or large deep horizontal collectors.