What is an air source heat pump?
An air source heat pump (ASHP) is used to provide a home with heating and hot water. An ASHP absorbs heat from outside air in the same way that a fridge extracts heat from its inside. This heat is then used for heating radiators, underfloor heating systems, or warm air convectors, as well as providing hot water.
Air source heat pumps can get heat from the air even at temperatures as low as -15°C.
How does an ASHP work?
An air source heat pump works by absorbing heat from air outside at a low temperature into a fluid which is passed through a compressor to increase its temperature. The most common air source heat pump is an air to water system, where the higher temperature of the fluid is transferred to the heating and hot water systems in a property.
What are the benefits of air source heat pumps?
There are many benefits available when utilising an air source heat pump system:
- The cost of running an air source heat pump to heat your home is considerably less than most alternative methods, such as oil, LPG or conventional electric heating;
- An air source heat pump has a low carbon footprint as it uses a natural source of renewable energy;
- The energy you generate with an air source heat pump can be used to heat your home and provide hot water;
- Having an air source heat pump will remove the need for fuel deliveries if the house is off-grid with no mains gas.
Types of air source heat pumps
As well as air source heat pumps, there are three other alternatives:
- Ground source heat pumps: Using the earth as a heat source, ground source heat pumps utilise the stable temperatures in the ground to supply a property with heat and hot water
- Water source heat pumps: These are similar to air source and ground source heat pumps, but take heat from relatively consistent temperatures found in a body of water, such as a lake, river or stream;
- Solar-assisted heat pump: This system combines thermal solar panels with a heat pump in a single integrated system.
Costs and savings
There are various factors to take into account in order to calculate how much an air source heat pump will cost and what it could save you.
How much does an air source heat pump cost?
The estimated cost for the installation of a standard air source heat pump system will vary due to a number of factors including the size of your space, how well insulated the property is, the way you use your room space and what room what room temperatures you wish to reach. Therefore we would always recommend that you obtain quotes from a range of reputable and accredited installers. Click here to find accredited HIES members in your area who can help with your project.
What could you save?
The savings you could achieve will depend on a number of factors. Utilising underfloor heating can be a more efficient heat distribution system than radiators as it removes the need for the water to be heated to a higher temperature as much.
Because electricity is necessary to power an air source heat pump, you will still need to pay fuel bills, but these could be much lower than the fuel that you are replacing. Also, if your current heating system is inefficient, you will more likely experience reduced running costs with an ASHP.
Once you have installed an air source heat pump, it’s important to learn how to get the most out of it through the control system. Although it might be necessary to set the heating to be on for a longer period of time, it’s possible that you will be able to set the thermostat to a lower temperature and still feel comfortable.
Air source heat pumps deliver heat at lower temperatures over much long periods, unlike oil and gas boilers. At colder times of the year, you may have to keep the heating on continuously in order to properly heat your property. Increasing the insulation of your home will trap more heat and reduce the energy required to warm the room space.
The lower the temperature the air source heat pump is working at the more efficient it will be and therefore will use less electricity to run. The table to the right provides you with an illustrative example of the efficiency of an air source heat pump at different temperatures.
The lower the temperature the air source heat pump is working at the more efficient it will be and therefore will use less electricity to run. The below table provides you with an illustrative example of the efficiency of an air source heat pump at different temperatures.
As you can see from the table if the air source heat pump is running at a temperature of 35oC then it is 401% efficient, meaning for every 1kWh of electricity the air source heat pump uses it generates over 4kWh of heat. If it’s running at 55oC then it’s 318% efficient.
|Flow temperature||Efficiency (%)||Flow temperature||Efficiency (%)|
Grants & financial support
Domestic Renewable Heat Incentive
If you install an air source heat pump, then you may be eligible to receive regular cash payments for the heat you generate over seven years through the Renewable Heat Incentive (RHI), the UK Government scheme to encourage the uptake of renewable heat technologies.
Please note, the DRHI is now closed to new applications.
Boiler Upgrade Scheme
Recently, Government has announced plans for a new initiative known as the Boiler Upgrade Scheme which looks to reduce the cost of low carbon heating technologies, such as heat pumps, so that they are more affordable for consumers to buy and run. As part of the Scheme, a £5,000 grant will be available for air source heat pumps for those who meet the eligibility requirements. Find out more here.
Underfloor heating or radiators?
Air source heat pump systems operate at lower flow water temperatures, this may be 35oC to 55oC compared with 65oC to 80oC for a gas or oil-fired system.
Underfloor heating (UFH) is often the most effective way to heat rooms with an air source heat pump system. UFH heats the whole floor area at the lower temperature and because warm air rises, it radiates the heat into the room.
If underfloor heating isn’t being used, or possibly being used downstairs with radiators upstairs, it is advisable to use larger radiators to heat rooms in these areas. Large radiators create a bigger surface area to heat the room effectively at a lower temperature over a longer period of time.
Calculate the system size for your house
An air source heat pump comes in various sizes. The size that is right for your home will depend mainly on two things – the size of your house; and how efficient your house is at keeping heat in. In order to calculate the correct size for your property, this will usually involve the installer carrying out a room by room assessment of your home.
The installer will calculate the size of each of your rooms along with the material fabric of the walls and details of any windows. It would normally take the installer 1-2 hours to undertake this which will help identify the size of air source heat pump that is right for your property.
Things to consider
- Efficiency: The Coefficient of Performance (CoP) varies between different air source heat pumps. The higher the CoP the more efficient the air source heat pump will be.
- Noise: Air source heat pumps are not silent. They produce a noise similar to that of an air conditioning system. So, while they’re not overly noisy, it would be wise not to situate them somewhere that proves problematic.
- Planning permission: Air source heat pumps usually don’t require planning permission as they’re typically listed under permitted developments. However, in order for this to be the case, certain criteria has to be met, mainly in relation to the neighbouring properties. It’s always prudent to check with your installer and planning authority before you begin any installation.
In order to get the best out of an air source heat pump system, it is necessary to install a suitable cylinder. This will have a much larger coil capacity than a standard cylinder, making it capable of heating an increased surface area.
Underfloor heating is an ideal way of getting the maximum efficiency out of an air source heat pump system. Pipes are installed underneath floorboards for the hot water to flow through, heating your home to a comfortable temperature. Underfloor heating can be more efficient than radiators as the water doesn’t need to be so hot. You will need to ensure that when installing underfloor heating the spacing between the pipes isn’t too great as this will then create cold spots on the surface and you may need to turn the temperature up which reduces the efficiency of the air source heat pump.
Air source heat pumps work better at lower temperatures and this means that they are most effective when used in conjunction with larger radiators. It is possible to use standard-sized radiators but this will require the water to be heated to a higher temperature and affect the overall efficiency of the system.
Find an installation company
You should always choose a reputable installation company to fit your air source heat pump system. All HIES Accredited Installers are continually vetted in many areas in order to give consumers trust, confidence and peace of mind.
Questions to ask
It’s worth thinking about your main motivation to install a new heating and hot water system. Once you understand the key incentives behind your enquiry then it will help you find what you are looking for.
You should ask yourself, and an expert installer, some key questions to be certain that an air source heat pump is the correct renewable energy solution for you.
- Do I have enough space? Air source heat pumps require significant room in order to operate efficiently and need to get a good flow of air, ideally in a sunny spot. They can be fitted to a wall or located on the ground.
- Is my home insulated enough? Your property must be well insulated and draught-proofed for an air source heat pump system to work well as they function most efficiently when producing heat at a lower temperature than traditional boilers.
- Gas or electric? An air source heat pump system might not be the ideal choice for properties that utilise mains gas, but it could prove an excellent option if replacing an electricity or coal system.
What heat emitter system should I choose? Because of the lower water temperatures required by an underfloor heating system or warm air heating, air source heat pumps work much better in those situations rather than with a radiator-based system.
Combining an air source heat pump with your existing renewables
Electricity is required to operate an air source heat pump system, but you can help power them by an alternative method such as solar panels, wind turbines or micro-hydroelectric.
Homeowners are starting to look at installing air source heat pumps along with solar panels as a complete package, helping to lower fuel bills and cut their carbon footprint.
Solar panel electricity systems, also known as photovoltaics (PV), capture the energy from the sun using photovoltaic cells. This electricity can then be used to operate an air source heat pump, creating an independent system.
Electricity is required to operate an air source heat pump system, but you can help power them by an alternative method such as solar panels, wind turbines or micro hydro-electric.