What is a Heat Pump and how do they work?

A heat pump is basically a system which transfers heat from one location to another. It is a highly energy efficient system and uses electricity to operate the components (but not to actually create heat).

Heat pumps use a similar system to fridges, but in reverse. They carry warmth to a cooler location and use a refrigerant liquid to transfer this heat.

There are 2 main types of heat pump – air and ground – named for the source of the heat they transfer.

They are thought of as environmentally friendly as no fuel is burned, and are certainly better than most of the other options available as the electricity is not used for actual heat creation. They are now often used for new buildings and premises where sustainable building is considered.



Heat pumps use a refrigerant liquid, which is pumped between the warm and cool areas and evaporates and condenses to transfer the hear.

Heat pumps are actually quite simple and have 4 main components:

  • Condenser
  • Evaporator
  • Compressor/Pump
  • Refrigerant Liquid

At one end of the system, the refrigerant liquid is evaporated and absorbs heat due to the low pressure. The compressor pump them moves the liquid through to the condenser, whilst increasing the pressure. The liquid is then condensed due to the high pressure, and releases its heat into the surroundings.

At low pressure in the evaporator, the liquid can absorb heat even in incredibly low temperatures, making it a great system even in winter.



Air source heat pumps are usually positioned on the exterior wall of a building. The aim is to gather heat from the sun and surrounding air to transfer into the building. Air based heat pumps usually have a fan to keep a flow of external air running over the evaporator for the liquid refrigerant to absorb heat from.

Ground source heat pumps actually have part of the system in the ground to gather thermal energy, stored in the earth from the sun’s heat. These are often a water based system, with water flowing past the evaporator in a looped piping system to allow the transfer of heat – just like the fan in the air based system. Ground source water piping systems can be laid flat to the ground, or vertically into the soil.

Ground source heat pumps require a considerably larger amount of space, time to install and cost, but are more efficient, quieter and not visible.




  • Government subsidies may be relevant to these systems – there are some for commercial premises and some for domestic.
  • They work throughout the year where temperatures are not too extreme (the UK is perfect for this)
  • Energy efficient way to heat a building – low emissions and low energy use
  • Potential to increase property value
  • Air source heat pumps can be installed very quickly


  • Space required for ground source pumps can be quite large
  • The capability of the air source heat pumps is lessened over a ground source heat pump
  • Heat pumps are more suited to a well-insulated property, and will not be as effective in older, draft-prone premises
  • Ground source heat pumps can be expensive and time consuming to install
  • Air source heat pumps can be noisy