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Air Source Heat Pumps

Air source heat pumps are easy to install in new build or retrofit into existing properties. They can provide effective space heating and hot water for homes and commercial properties. They are also a very efficient way of heating swimming pools.

Air source heat pumps collect heat from the air so there is no need to install an extensive ground loop (ground heat collector). This allows for a much simpler, quicker installation. Air source units can be sited within, close to, or a distance of up to 50m away from the building, whatever is most appropriate for your project.

How it works



The temperature of the air varies quite considerably from summer to winter and there is more heat in the air during the summer which is easier to extract than it is in the winter, so air source heat pumps have to work harder during the winter months. However, even when the air temperature is below zero the heat pump is still able to extract heat from it. Because we are all so familiar with the Celsius temperature scale we are all conditioned to think that anything higher than zero degrees (the melting point of water) is warm and every thing below zero is cold. However, in actual fact anything that is above absolute zero (-273 degrees celsius or 0 kelvin) contains heat. There is a limit to how cold the air can be before the heat pump stops working but they are designed to still be able to extract heat from the air on a cold winters day.

Some of the key differences between heat pumps from different manufacturers come down to how efficiently they operate at low air temperatures, so this is where correct design and installation of the air source system is essential to ensure that they work as efficiently as possible for your particular property. An air source heat pump that is suitable for a property in the North of Scotland would be unlikely to be suitable for an identical property on the South Coast of England.

A heat pump uses the same principle to transfer heat that fridges use.  Fridges keep cool by pumping heat away from food and drink to the grill on the back; heat pumps extract heat from the renewable source and pump it into buildings.  A refrigeration cycle uses the renewable energy that is extracted from the air, ground or water to boil a special liquid refrigerant into a gas, these liquids have a boiling point that is much lower than that of water.  The gas produced is then compressed and becomes hot and the heat is extracted, this then turns the gas back into a liquid again and the cycle starts again.  The generation of heat by compressing a gas can be seen with a simple experiment of trying to pump a bicycle pump with your thumb on the end, as the air is compressed the pump will become hot.

How reliable are heat pumps and how much maintenance do they need?

Heat pumps have been widely used in Europe and North America for decades.  Because the refrigeration cycle is a tried and tested technology they tend to be extremely reliable.  However, in order to ensure they continue to run as reliably and as efficiently as possible we always recommend servicing them annually, just as you would a conventional boiler.

Why are heat pumps becoming more commonly used?

Traditionally the UK had plentiful supplies of fossil fuels; oil and gas from the North Sea and extensive coal workings. However, there are two main issues with this:

  1. Burning fossil fuels releases climate changing carbon dioxide that had previously been locked away underground.

  2. Energy prices are rapidly rising as the UK increasingly imports oil and gas from abroad.

Heat pumps are a very efficient way of indirectly using electricity to heat a home by extracting available heat from the ground or air and as such can provide low running costs and low carbon heat.  Typically every unit of electricity used to drive the heat pump can provide three or more units of heat. 

Temperature of the hot water produced

Heat pumps are very efficient at heating water to around 40 degrees celsius.  As such they are ideal partners for underfloor heating systems which typically require a flow temperature of the same.  Heat pumps work less efficiently when heating water to higher temperatures and as required by the direct hot water in your home, but they will still readily maintain a hot water cylinder to a temperature of around 55 degrees celsius which is hotter than would be required for a bath or shower.  Heat pumps also automatically run periodic legionella cycles to ensure that any bacteria that might still survive at 55 degrees are definitely removed.


Heat pumps require little by way of maintenance.  It is important to ensure that the external fan unit is clean and free of leaves or other such waste or vegetation that could impede the flow of air through it, particularly in autumn as leaves are falling and the system is starting to work harder as the colder weather arrives.  The heat pump itself is a sealed system and doesn't produce any waste gases, ash or moisture.  It is recommended that the heat pump be serviced annually by an accredited company to check things like the refrigerant levels and that the system is still operating as efficiently as expected, but other than that it should be maintenance free.

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