Air to Water Heat Pump

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Green Homes Grant 2020 - Applications are now open.
Last updated: 09 October 2020

How Does an Air to Water Heat Pump Work?

Air to water heat pumps take heat from the outside air and transfer it to a water-based system. The created heat can be used for space heating or as a hot water supply for the house. Air to water heat pumps are among the most efficient air source heat pumps on the market. 

This type of heat pump works best in moderate climates. The efficiency of an air to water heat pump is most optimal at 7°C, as opposed to dry and cold locations, where outside temperatures fall below -20°C. Keeping the working principles of an air to water heat pump in mind, the decline in temperatures will affect the operating efficiency.

In climates with very low winter temperatures, ground source heat pumps may seem a more suitable choice, as they extract heat from the ground and perform well in freezing cold temperatures. However, the technology developments for cold climate heat pumps using the air to water principle, are said to cover heating needs even with a low temperature set point of below -25°C.

Choosing the right heat pump depends on the needs of the house. An air to water heat pump, as well as the other types, have one important advantage in common — they produce renewable energy, as the ground or air are technically heated by the sun. Both air to air and air to water heat pumps use a similar operation model.

Considering the pros and cons of air source heat pumps, they are still more efficient than an old gas or oil system.The air to air type circulates warm air using fans and can only be used for space heating, unless combined with an external heating system.

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Air to Water Heat Pump

If you are keen on choosing a complete solution for domestic heating and hot water supply, do not hesitate to contact us by filling in the form on the right. We will match you with the right suppliers of air to water heat pumps that fit your needs. Compare up to four quotes from different suppliers and make informative decisions. This service is free and non-binding

How Efficient are Air to Water Heat Pumps?

By using an air to water heat pump, you are reducing your carbon footprint by 50%. This is because, although it runs on electricity, it mainly uses replenishing green energy. It captures low grade air, which is then transferred within the system, and generates optimal heating and hot water for your home.

Air to Water Heat Pump System


In order to get the best value for money, planning your installation carefully is a must, regardless if it’s in a renovation or new construction property. Air to water heat pumps work very well with underfloor heating, as they operate at lower temperatures.

Initially, costs of underfloor heating systems combined with a heat pump can seem as a serious investment. However, within the first year of installation, you will be able to see the differences with lower electricity bills, and increased comfort in your property.

Air to water heat pumps can be considered even if your existing heating systems use water-based radiators. If you don’t want to upgrade, it’s worth noting that the efficiency of the heat pump combined with radiators will depend on them being properly sized for the heating demand. Larger size or double-panel radiators will be most suitable in this case.

Is a Domestic Air Source Heat Pumps Expensive to Run?

The price of an air to water heat pump is around £8,000-£18,000, including the system and installation price. Installation and running costs depend on the following factors:

  1. Size of the property
  2. Heating demand
  3. New Build or renovation 

According to the size of the property, you can determine the needed heating demand. This will give you an idea of the most suitable air to water heat pump for your home. Other factors, such as the state of the property will affect the associated costs, especially with insulation. Let's have a look at more detailed running costs breakdown below.

Running Costs and Savings
Property Type Annual Heating Cost RHI Payback Per Year Annual Savings
2 Bedroom Teracced House Starting from £329 Up to £670 Starting from £335
3 Bedroom Semi-Detached Starting from £495 Up to £1,000 Starting from £500
4 Bedroom House Starting from £759 Up to £1,600 Starting from £700

*Estimations are based on an air to water heat pump with 3.7 SCOP and a household with good quality insulation. The tariff used is an average UK electricity price of 14.37p/kWh, and an RHI tariff for Air Source Heat Pumps of 10.71p.
**Prices are based on averages and should be treated as a guide only

In comparison, system and installation prices of ground source heat pumps start from around £13,000 and can go up to £40,000. Considering the visible price difference between the two heat pumps, RHI payments also vary from type to type.

Domestic RHI payments for an air to water heat pump can be around £9,000-£10,000, whereas for ground source heat pumps, domestic RHI payments could be over £25,000, made on quarterly payments over 7 years.

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Are There Air to Water Heat Pump Grants?

In the UK, the Renewable Heat Incentive helps reduce your air to water heat pump's running costs. It's a government grant that encourages the uptake of renewable heating technologies.

Through the domestic RHI, households in the UK can receive financial support through a tariff, and payments last for seven years. The current tariff for an air to water heat pump is 10.85p/kWh. This support will significantly reduce the running costs of your air source heat pump. 

The domestic RHI is scheduled to close for new applications on 31 March 2022.

Another grant that is currently available is the Green Homes Grant. Through this grant, landlords and homeowners in England can reduce the installation cost of an air to water heat pump by two-thirds, or up to £5,000. This grant is said to close on 31 March 2021.

The RHI and the Green Homes Grant can be combined, though it is important to know that if you do receive the installation voucher, that amount will be deducted from your RHI payments. This means you will not reap the full benefits of the RHI, as you will have to 'pay off' the voucher through your RHI payments.

Advantages and Disadvantages of Air to Water Systems

Air to water heat pumps are a great choice for distributing heating and hot water to your house, with minimal environmental impact. By using a renewable solution, you will save on your bills over time, and furthermore, the RHI incentive will cover a large portion of your costs over time. If you want to estimate your savings, Ofgem, the governmental electricity and gas regulator update their RHI tariffs periodically. In order to make an informed decision about the perfect system, let's have a look at the pros and cons of air source heat pumps


Installation planning for air to water pumps is easier, as they are smaller and don't take a lot of space. However, they have twice the energy efficiency of a bulky oil or gas system. Given that air to water heat pumps uses air to generate energy, the operating system is simple and risk-free.  Properly sized and good quality air source heat pump will save you on electricity with low heating costs, but it won't compromise on the heat output and comfort


Air source heat pumps are at risk of inefficiency when operating in very cold weather conditions, so it will be best to look for a different main heating system that will provide sufficient heating. And if you considered investing in an air to water unit because they are compact and easy to maintain, consider the high levels on noise before placing the inside unit elsewhere other than in the utility room. Another planning consideration is the cost for good insulation, as this will have the biggest influence over your future savings by using an air to water heat pump.


  • Compact and relatively small in size
  • Family-friendly and safer than combustion-based systems.
  • Ecological choice, as they produce energy by processing air.
  • Generate more energy than the the electricity they consume to operate.


  • Another main heating system needed in very cold locations.
  • Older models have high noise levels while operating.
  • Decreased efficiency when operating in temperatures below 6°C.
  • Optimal performance depends on good quality insulation of the house.

4 Factors to Consider When Installing Air Source Heat Pumps

The key to a properly functioning heat pumps lies in the correct sizing of the heat pump, according to your property’s heating demand. Homeowners who wish to apply for an RHI grant should also consider the fact that their air source heat pump needs to be installed only by an MCS certified installer companies and some additional requirements may apply. 

To ensure that your air to water system will operate at its full efficiency, you should take into consideration the following four factors:

1. What’s Included in the Installation Price

When asking for an offer, make sure that the installation and introduction costs are included in the air to water heat pump price. Your savings will highly depend on your specific heating needs, the size of your air to water heat pump, and your heating system.

Your geographical location, as well as how humid the air around your home is, can each affects your heating savings.

2. Professional Air to Water Heat Pump Installation

Installation of an air to water heat pump can take only a few hours, but it needs to be done by a professional installer, which you will find to be a requirement from many air to water heat pump manufacturers. Contact your electricity supplier to find out if any changes should be made to your existing system.

3. Keep the System Clear of Obstructions

The outside part of the air to water heat pump should not be located in a closed or narrow space, because the air has to circulate around the machine, and when the air has once been through the machine, it should not enter it again. The inside part of the air to water heat pump can, for example, be located in a utility room in the house, as long as there is a floor drain in the room.

4. Heat Pump Noise

Noise levels of air to water heat pump are approximately 40-60 decibels (depending on the system) from a distance of one metre away. This is a factor that needs to be taken into consideration when choosing the location of installing the heat pump, especially on older models. It’s good to keep in mind that larger heat pumps’ fans will run on faster speed, and thus will make more noise. 

Maintenance and Care for Optimal Performance

Proper maintenance and care will ensure that the system is operating at its full potential. The outdoor unit needs to be kept free of debris in order to last longer. Make sure that:

  1. The filter in the outside component should be regularly cleaned, to ensure that the system is using clean water and to avoid damage.
  2. The unit should be kept dry and the area around it kept clean, to ensure proper air inlet and outlet.
  3. The water tank should be cleaned with scale (depending on local water quality), and the system should be regularly checked for leakage.

FAQ about Air to Water Heat Pumps

We measure the performance of air source heat pumps by their Coefficient of performance. The higher the number, the greater efficiency. Average COP of 3 for an air source heat pump, means that your system will generate 3kW for 1kWh of electricity used.

SCOP (Seasonal Coefficient of Performance) is a newer measurement that describes the average COP in a heating season.

As we mentioned before, taking care of your heat pump will keep the unit working at its best. Changing the filter and removing any leaves or other objects around the outdoor unit will ensure to keep the efficiency levels high.

Yes, you can save a good amount by applying for air source heat pump grants. The Domestic and Non-domestic Renewable Heat Incentives are available in England, Wales and Scotland, and they provide quarterly payments paid over 7 years. Current tariffs and payments are available on Ofgem.

There are currently two grants available for air to water heat pumps. Under the Renewable Heat Incentive (RHI), you can receive financial support over the course of seven years. The domestic RHI is scheduled to close on 31 March 2022.

The Green Homes Grant is another government grant, which covers two-thirds of the installation cost of your heat pump system. This scheme will close on 31 March 2021. The RHI and Green Homes Grant can be used together, though the amount you receive for your Green Homes Grant will be deducted from your RHI payments—meaning you will effectively be paying off the voucher through your RHI payments.

10-15 years. This of course depends on factors such as the brand model, location and maintenance of the unit. They normally come with a warranty of two to three years.

With proper insulation and proper air to water heat pump size for your home, you don’t have to leave it on all the time. You can use a timer which will automatically turn on and off the unit, depending on your heating needs.

Planning permissions are not usually required for air source heat pump systems as of 1 December 2011, given that certain requirements are met.

If you wish a professional assistance for choosing the right air to water heat pump system, GreenMatch is here to help you! By filling in our contact form at the top of this page we will come back to you with up to 4 quotes from suppliers near you. The service is non-obligatory and free of charge!

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Written by Ramona Gosheva Content Writer Ramona is a Content Writer at GreenMatch with a keen focus on environmental awareness and sustainability. Her educational background is in Creative and Media Writing, and has experience in events and content creation for various mediums.
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