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Air Source Heat Pumps & Ground Source Heat Pumps explained
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How They Work

Heat from the outside air is captured via a specialized fluid being pushed around the system by a circulatory pump and then sent through a compressor to raise its temperature. The now hotter fluid is then passed through a heat exchanger and is sent to a hot water storage cylinder which in turn provides the supply for domestic hot water and via a buffer tank or low loss header, the heating system for the property.

Two Ways To Use That Heat

Air source heat pumps (ASHP) work a little like a refrigerator, only backwards, and do exactly what it says – they take heat from the ambient outside air, squeeze it in a compressor and send it to a purposely designed hot water cylinder for your domestic hot water supply or to fulfil your home heating requirements. There are two basic ways to use this heat;

  1. Air to Water – with this method, the heat is sent to a wet central heating system, usually a gas or oil boiler with traditional convector radiators. The heat in the air pump fluid is of a lower temperature than that of a traditional boiler method so it is ideal for underfloor heating (UFH) which requires less heat but can sometimes require the installation of over-sized radiators in order to emit a comparable level of heat throughout the room or property. There are various schools of thought on whether the heat pump should remain in operation 24hrs a day or not. As it provides a lower level of immediate heat, it takes time to rewarm a cold house with solid walls etc so some people leave them on constantly.

  2. Air to Air – This method uses the heat produced by the air source pump to circulate warm air throughout your property via specially installed ducts. These are occasionally found in brand new modern homes however this style of system is unlikely to be suitable as a retrofit due to the probability of unsightly ducting and also the inability to provide domestic hot water.

Is Your Property Suitable for An Air Source Heat Pump?

An air source heat pump will not be the best choice for every single home. The following are some points to consider if they are right for you;


  1. How do you heat your home now? – Air source heat pumps are far more economical now, financially & environmentally, than they used to be especially when set against coal, electric, oil-fired or gas-fired heating systems, in particular Liquid Petroleum Gas (LPG).

  2. Where will it be installed? – Evidently, as the air source heat pump requires a never-ending supply of air, it has to be located outside on anti-vibrating mounts on the ground in a garden area, back yard or perhaps fitted to a suitable wall. Wherever it goes, it will need to be safe and secure, away from mischievous hands!

  3. Have you got suitable insulation? – As air source pumps produce heat at a lower temperature than traditional systems, it is very important for your property to well insulated to keep that heat in. Government grants may be available to cover some or all of the cost to add thicker insulation in a loft, to fill the void in cavity walls, to add solid wall boarding etc etc. 

  4. How will the heat be distributed around your home? – If you are planning to use your existing pipework system, you may well need to increase the heat emittance area of your radiators – in other words, you might need bigger ones! This is because the heat pump produces hot fluid at typically around 45 – 50 degrees C. You might need bigger radiators to achieve a comparable level of comfort and is a cost that should be born in mind during your considerations.

Under Floor Heating (UFH) is a great way to ground floor levels of a property as it is specifically designed to run at lower temperatures. This is another cost to consider when deciding your style of system.











Other Considerations – 

Before deciding to install an air source heat pump, there are a few more things to be aware of. On the ‘Pro’ side, they are a lot quicker & cheaper to install than a Ground Source Heat Pump (no expensive digging of trenches or channels through your garden or land). On the ‘Con’ side, they have less fuel savings than a GSHP although if you currently use coal (probably rare these days), electricity or LPG, there are still potential savings to be made.

Remember the mention of the refrigerator at the beginning? Most air source units can be run in reverse to behave like an air conditioner or more precisely, a cooler, subject to the correct style of ‘fanned’ radiators being installed.

In Conclusion –

If you happen to be living off the gas grid, have no access to LPG, oil and your solar panels are'nt producing enough to heat your water, then an air source heat pump could be for you. With a cost that could be repaid by the Government RHI grant working out at a lower cost over several years, together with being greener for our environment. You do need to think of where the heat pump will be located ie away from annoying the neighbours! Think about noise levels and maybe any system improvements required. Don’t forget room for a large cylinder and lots of associated pipework inc buffer tanks, low loss headers and necessary pipework!! As a lower cost system, they are more affordable than ground source.


Click here for Domusa Air Source Heat Pump Products


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