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Air Source

Heat Pumps

Harnessing the invisble energy within the air we breathe to heat your home

For those without the space to accommodate ground loops or those who can not bear the expense of having boreholes installed, an Air Source Heat Pump (ASHP) is the ideal path to sustainable energy and lower running costs.

How do they work?

Air source heat pumps use a fan and a compressor to absorb thermal energy that is held in the air outside.


Large fans are used to draw in the air and pass it through a finned heat exchanger, where it heats a water/anti-freeze mixture. Thermal energy is absorbed by the refrigerant which then passes through a compressor.


The process of compressing the refrigerant without allowing it to occupy a greater volume increases both its pressure and, most importantly, its temperature! This compressed and heated refrigerant then passes through another heat exchanger where it transfers its thermal energy to the system inside the house.

Internal Requirements

Some space must be set aside for a hot water cylinder and a buffer tank . The size of these components depends very much upon the size of the space to be heated and the anticipated occupancy of the building.

The hot water cylinder stores water heated by the heat pump and provides instantaneous hot water to your taps and showers when called for.

The buffer tank stores warm water generated by the heat pump to be used by the home's heating system. The buffer tank ensures the heat pump's requirements for minimum flow-rates and total volume of water in the circuit are met even if there is little demand from the heating system, increasing the heat pump's efficiency and lifespan.

External Requirements

As the name suggests an air source heat pump is positioned outside and is best positioned near the property so that the length of pipework from heat pump to cylinder can be kept as short as possible without compromising the steady flow of air.

Ideally the heat pump will be positioned in a 'sun-trap'. A sunny external wall is ideal as it will absorb the heat from the sunshine and re-emit it, warming the air nearby and providing the heat pump with a better starting point in terms of the pre-compression temperature of the refrigerant.

To allow adequate drainage of condensation the compressor unit should be installed on a concrete plinth with gravel around its footings. Please get in touch for details on how this should be constructed. If the unit is to be installed on a roof then the roof's standard drainage design should be more than sufficient to handle the condensation produced.


A useful video by the Energy Saving Trust explains Air Source Heat Pumps in more detail.

What else should I consider?

You may wish to consider a Ground Source Heat Pump instead if you have enough space. They are more expensive to install but deliver a higher co-efficient of performance and greater RHI payments in return.

If you have a body of water you should also consider installing a Water Source Heat Pump.

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