How do heat pumps work?

They take the ambient heat from the ground, typically, and concentrate this for use in your home.

This heat can be used to heat your home directly or heat water to feed into your central heating or hot water system. This reduces the amount of fuel you need to burn for heating, saving you money. The government are supplementing the cost of installation for ground source heat pumps with the RHPP scheme, offering one-off grants of £1,250.

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Technical information made simple

You will need enough outside space to bury a loop of pipe called a ‘ground loop’ which collects the heat from the earth, although they can be buried in vertical boreholes if space is really tight.

  1. A mixture of water and antifreeze circulates around the ground loop – which is buried in the garden. This absorbs the heat from the ground.
  2. Then the heated ground loop fluid is pumped through a heat exchanger passing the heat to the refrigerant.
  3. The refrigerant is compressed and the heat concentrated into a higher temperature in a compressor. This makes it hot enough to heat water for either heating or hot water.
  4. The ground loop fluid, now cooled, passes back into the ground where it captures more heat and repeats the whole process.

The size of your home, and your requirement for heat will determine the length of the ground loop – longer loops can draw more heat from the ground, but need more space to be buried in.

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There are other types of heat pump and they work on a very similar principle, but tend to draw heat from different sources:

  • Air Source Heat Pumps: They draw heat from the outside air and are popular as they are cheaper and easier to install, particularly if you live in a city with limited outside space.
  • Water source heat pumps: This is very similar to a ground source system except that the ground loop is immersed in water, such as a lake or river.
  • MVHR (Mechanical Ventilation and Heat Recovery): This is effectively exhaust-air-source; these recover the heat from air leaving your home via vents. This is most effective in more air-tight homes.

Installation

In order to qualify for the RHPP scheme the system must be fitted by a MCS accredited installer. Find out more about the Installation of ground source heat pumps.

FAQs

How are the ground loops installed?
The ground loop is either buried in trenches in the land outside your house at a depth of 1.5-2m or installed in boreholes that range from 25-150m deep. They can also be placed in lakes or ponds to capture the heat from the water - this is usually used on large estates.
Where should I put my heat pump unit?
Usual locations include your utility room, basement or even out in the garage.
Can a ground source heat pump be used with underfloor heating?
Underfloor heating is a great choice for use with a ground source heat pump, but large radiators or a mix of both can be used for distributing heat around your home. Heat pumps produce a lower temperature heat than conventional boilers, therefore they are far more effective if used with a larger surface heating distribution system such as underfloor heating or large radiators. A good rule of thumb is that if used with heat pumps, the radiators should be around 30% larger compared to the size of radiator that would be used with a conventional boiler.
Can a ground source heat pump be used to cool my house?
Yes, in some ground source heat pump systems this can be achieved as either passive or active cooling.
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