Air Source Heat Pumps Guide - VIVA Training Academy

With most home heating systems generating heat by either converting electricity or burning fuel, air-source heat pumps do not generate heat. The heat pumps are a renewable energy source moving heat energy from the outside air into homes. They deliver more heat energy than the electrical energy they use hence more efficient.

What is an Air Source Heat Pump

ASHPs are used to generate renewable energy by absorbing heat from the air outside into an indoor space such as an office or a home. They work similarly to refrigerators that are absorbing heat and transferring it to another channel. In addition, some heat pumps work as cooling systems.

The heat pumps should be placed outside of a building with adequate space to extract heat from air with temperatures as low as -150C. ASHPs require electricity to operate, but the electricity input is less than the heat output. This is because the heat pumps extract renewable heat from the environment hence an energy-efficient heating method.

Ground source heat pumps should be considered where there is ample garden source outside. Even though they require intensive installation costs, they are very efficient in heating homes with low energy bills and high fuel savings.

How Air Source Heat Pumps Work

ASHPs work typically as the reverse of a refrigerator:

  • The air from outside is blown over a system of tubes with a refrigerant.
  • The refrigerant is turned into a gas from liquid through warming.
  • To increase the pressure of the gas, it is passed through a compressor.

Similarly, as the air hose is warmed up when the air pressure is added to the tyres, compression adds more heat by increasing the temperatures.

The hot gas is then passed into a heat exchanger surrounded by water or cool air. The water or cool air acquires heat from the refrigerant and becomes warm. Finally, the warm air or water has circulated the home to provide heating.

The refrigerator then condenses and becomes a cool liquid, and the cycle starts again.

Types Heat Pumps

Air to air and air to water are the two main types of heat pumps. The type of ASHPs chosen is determined by the heat distribution needed.

Air to Water Systems

These heat pumps soak up the heat in the air and then transfer it to water. The heat is distributed via a wet central heating system to provide either hot water heating, underfloor heating or radiator heating in your home or all three. They give out heat at lower temperatures over a long time because they are suitable for large radiators or underfloor heating systems. This is the most common model of Air Source Heat Pumps in the UK.

Air to Air Systems

The heat absorbed from the outside air is directly transferred into the home through a fan system as they require a warm circulation system to distribute the heat around. These heat pumps do not provide hot water as well. As a result, the pumps are not permitted for the UK governments Renewable Heat Incentive (RHI) scheme, and homeowners who have installed these heat pumps are not eligible for the incentives.

Cost of Air Source Heat Pumps in the UK

ASHPs cost more than oil fired central heating system or new gas. The cost of a typical air source heat pump depends on the heat output and the pump brand. The cost ranges between £4,000-8,000.

Installation Costs of ASHPs

In addition to the above costs, there are other installation costs which you will have to incur too, which brings the total costs to approximately £5000 and £10,000. Other costs like installing a new air distribution system or new underfloor heating should also be factored in determining the total costs.

Cost of Improving Home Insulation

In cases of draughty or poorly insulated homes, the costs of improving insulation should also be included in the total costs. This is necessary because air source heat pumps are not effective in a home with poor insulation.

Generally, air-source heat pumps require high beforehand investment. However, despite the significant upfront investment, they are one of the most efficient ways of heating your home. This is because ASHPs produce more heat energy than electrical energy consumed. As a result, their efficiency is three to four times higher than a modern gas boiler and electric heaters.

Cost of Running the Heat Pumps

The efficiency of the air source heat pumps relates to the cost of running them. The running costs of the heat pumps are far much lower than paying for a heating system. This is because heating a home with gas costs around 4-6p per kilowatt-hour (KWh) and 9-16p per KWh when using standard electric heaters.

It costs around 4.7p KWh to run a typical air source heat pump, but this rate can be as low as 2.3p KWh when using GoElec tariff or cheap rate economy seven electricity. It is difficult to give an exact amount for how much can be saved, say in a year, because of varying energy prices and home use patterns. However, the following example can be used to deduce how much can be saved in a year.

About 19000KWh of heat may be needed per year in a four-bedroom house which may cost about £874 in gas. The cost would be almost the same when using an air source heat pump and electricity costing about 16p per kWh. However, you could only save 25%, which is around £215, if you used the cheapest electricity rate even if you did half of the heating overnight.

When you consider hot water, the savings increase. Averagely, about 160 litres of water is used in a day by a four-person household, requiring an additional about 2800 kWh per year. This is another £129 using a 90% efficient gas boiler. You may only pay £65 if you get the hot water from an air source heat pump using cheap rate electricity.

The benefit of using an air source heat pump is homeowners can apply to be included in the Renewable Heat Incentive RHI, where the government pays such homeowners in Scotland, Wales and England for the renewable heat generated.

The payments last for seven years, with the most extensive system getting up to £1300 in a year. The upfront investment of an air source heat pump can be reduced by assigning your RHI income to a participating installer.

Air Source Heat Pump Installation

The following are a few steps to guide you when installing ASHPs.


The process begins with a thorough inspection of the property to ensure that the recommended heat pump is the most suitable for your needs. Next, an engineer may be appointed to visit the home and make a full assessment. Finally, the engineer will give recommendations and indicate the savings that one might make using the assessment.

The air source heat pump engineer will also assess other factors like the size of the home, installation level in the home, heating needs, and heat distribution in the home, whether underfloor heating or using radiators and other vital factors. To enable the installers to complete their work efficiently, detailed sketches of the rooms in the home will be used. After the proper inspection and the needs by the engineer, the installation process is set to begin. The following are the steps involved in the installation.

Installation of Indoor Units

This step will begin by choosing between the ductless and the ducted system. If a ductless system is obstructed on the wall inside the area to install, the contractor is located. A mounting plate will then be installed to hold the indoor unit and secure it to the mounting plate by the installer.

In the case of a ducted system, the indoor unit is connected to the ductwork by the installer. The contractors may do some repairs to maximize the efficiency of the heat pump system in case of existing ductwork. Where there is no existing ductwork, the first step will be installing one.

Creating an Access Point for Connection in a Wall

An access point is needed between the outdoor condenser and the indoor unit. A hole will be drilled in the wall by the installer to run lines and piping to create the access point. This will allow an outlet for the electrical and refrigerant lines and a condensate drain line that will take water from the indoor unit to the outside.

For a mini-split system, the hole dug on the exterior, and the room where the indoor unit was installed will be used. The access point in a ducted system is usually where the indoor air handler is located, often the basement or the attic.

Connecting the Indoor Unit to the Pipes

The next step is connecting the indoor unit to the condensate and the refrigerant lines. The refrigerants will be allowed to cycle through the outdoor and indoor condensers by the refrigerant lines. The lines will take cool or warm liquid to the indoor units depending on whether the heat pump is cooling or heating at the time. This will then force in the zone as air.

Installation of the Outdoor Unit

The contractor will install an outdoor unit once the indoor unit is ready. For larger central or packaged systems, the installers hold the outdoor condenser by putting a concrete slab on the ground. If an ASHPs with a minor system or a mini-split system, it will be mounted to the side of the home, which will be lifted above the ground. The installer will mount it above the possible snowlines in colder areas.

Connecting Electricity and Wiring

The installer will connect the outdoor and indoor units after being installed through the electrical and refrigerant lines. To protect the wiring from elements, the installers will insulate and run them through conduits on the sides of the house. A drain line will be installed on the outside to bring condensation away from the inside of the house.

Finishing Touches

To finish installing the system, a few finishing touches will have to be completed. One is to secure the pipes by affixing them to the sides of the home. Another one is to install sensors on your thermostat to communicate the temperatures of different zones. This sensor technology comes with many air source heat pumps. To adjust the temperature, they also come will wireless remotes. Therefore, changes can be done with an internet connection on your phone, tablet, or computer, hence easy monitoring.

Advantages and Disadvantages of Air Source Heat Pumps


  • Saves money- Switching to air source heat pumps means reducing energy bills as they use outside air to cool or heat your home.
  • Works in lower temperatures- The heat pumps extract heat from temperatures as low as -20 degrees. In temperatures of -30 degrees, it is revealed that air to air heat pumps can generate heat of up to 40 degrees. They are even more efficient in cold areas.
  • High seasonal coefficient of performance- It measures the heat pump’s efficiency by comparing the heat output to the power input. Despite some slight temperature fluctuations, the heat pumps run efficiently throughout the year, both in winter and summer.
  • Easy installation-It can take at least two days and is more accessible than installing a ground source heat pump.
  • Low maintenance cost- Maintenance and serving of the systems is only done once a year by a technician. However, to ensure efficient performance of the heat pumps, a few maintenance activities need to be done, like cleaning filters.
  • Extended lifespan-With proper care and maintenance, the heat pumps can last for up to 20 years. In addition, the pumps have a five-year warranty.
  • Does not need fuel storage-Unlike oil-fired boilers, which will require oil to be stored somewhere, air-source heat pumps do not require any form of fuel storage because the fuel used is the outside air.
  • Used for both space heating and heating water
  • Eligibility for RHI-generating own heat attracts payments and income through renewable heat incentive from the government.


  • Although they work in temperatures as low as -20 degrees, their efficiency reduces when temperatures fall below 0 degrees.
  • They can be noisy-When running, and in use, they can be very noisy.
  • They require electricity to run-This makes them semi renewable source of heat.
  • Requires a well-insulated home- To enjoy the system’s full benefits and for it to perform efficiently, the home must be well insulated.
  • They have a lower heat supply compared to gas boilers.

Heat Pump Energy Labels

Energy labels provide the customer with information necessary to facilitate the decision making process. In addition, they inform about the energy consumption of the heating sources.

They cover up to 50 KWh electrical power devices for heat pumps 70 KWh heating power and 500 litres storage tank capacity or a combination of the two with storage up to 2000 litres volume.

For a heat pump, information on the label include:

  • Manufacturer
  • Efficiency class
  • Function (heat\hot water)
  • Noise emissions
  • Heating capacity(KW)
  • Additional production of electricity
  • Number of model

Symbols can also be found on the labels. In addition to symbols, the following information may also be included.

  • Noise emissions on outdoors and indoors in decibel.
  • Heat pump information in Europe, including mid and low temperatures heat provision.
  • Nominal heat capacity

What to take into account

Before installing an air source heat pump, the following factors should e was taken into consideration.


Installation costs of a heat pump are usually between £8,000 to 18,000, with other additional costs being incurred depending on the system type chosen, specific requirements, and the home’s size. Compared to ground source heat pumps, whose costs range between £20,000 and 45,000, air-source heat pumps are way cheaper. Therefore, it is essential to consider the cost factor of the heat pump before installing it. This will allow you to budget appropriately and select the system type that is within your budget.


It is crucial to ensure that your home is well insulated for high returns in terms of saving. In addition, to allow for consistent warmth in the home, it is vital to ensure that the warmth generated does not escape, and this is only possible when there is proper insulation.


The first step in ensuring the heat pump is correctly installed is finding the right installer. Next, you need to conduct due diligence like checking the installer’s track record, the installer’s price being charged, and if the installer has all the required accreditations. All these three factors are essential before installing the air source heat pump.

Air Source Heat Pump Efficiency

The heat pump will produce for every 1KW of electricity inputted, 3KW of thermal energy. This translates to an effective efficiency of 300%. However, since it is impossible to have more than 100% thermodynamically efficiency, as this will imply more energy is being produced than consumed, the performance will be expressed as a coefficient of performance other than efficiency.

Therefore the coefficient of performance, in this case, will COP 3. More energy is being produced than consumed because the electricity used to drive the compressors and circulate pumps is the only valuable energy input. The other forms of energy such as ground, river or ambient air are not considered energy input.

ASHPs also have a high seasonal coefficient of performance, which measures heat pump performance considering varying air temperatures throughout the year.


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