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What is an Air Source Heat Pump? How Do They Work?

Adam Cherry
By: Adam Cherry
Updated: 8th March 2022

what is an air source heat pump?

What is an air source heat pump?
Air source heat pumps are a relatively new technology that can be used to heat your property in a more environmentally friendly and energy efficient way. As they use the ambient air outside of the property as their heat source, there is no need for a gas supply. This makes them a suitable heating solution for most homes, regardless of whether they are connected to the gas network.

How does an air source heat pump work?

There are 2 types of air source heat pump: air to water and air to air. This is how each of them works.

How an air to water heat pump works

Here is a step by step breakdown of how an air to water heat pump works:

  1. The heat pump has an outdoor unit, which contains a fan that draws air in from outside the property. This air then passes over tubes or coils filled with liquid refrigerant.
  2. The liquid refrigerant is much colder than the ambient temperature, even if the outside air is at sub-zero temperatures, and begins to heat up when air is passed over it.
  3. As the refrigerant continues to heat up, it becomes steam which is moved to a compressor. This compresses the steam which raises the temperature of the refrigerant even further.
  4. The heat of the refrigerant is then transferred to the water in the central heating system in your home, and any water stored in a hot water tank, for hot running water.
  5. The refrigerant, which has now passed on its heat, is then cooled and cycled back to begin the process again.

How an air to water heat pump works

Air to air heat pumps are essentially updated versions of air conditioning units that don't only cool air, but can also heat it. They work in the same way as an air to water heat pump, but transfer heat to the air in a ventilation system, rather than to the water in a central heating system.
A big drawback of air to air heat pumps is that they require a property to have air ducts installed throughout, in which to distribute warm air. They are also incapable of heating running water. This means they are not generally suitable for existing and older properties.

We have provided an in depth comparison of these heat pumps in our Air to Water Heat Pumps vs Air to Air Heat Pumps article.

Different types of air source heat pump

Not only are there air to water and air to air heat pumps, but each of these types of air source heat pump is generally available in different models. Namely monobloc air source heat pumps and split air source heat pumps.

Monobloc heat pumps

These are a large single outdoor fan unit which connects directly to the central heating system and will need to be located close to your property. There is no indoor unit, which can help to free-up space inside your property.

Split heat pumps

Split heat pumps consist of 2 main units: the outdoor fan unit and the indoor heating and cooling unit. These generally take up less space outside, but will require the use of some inside space.

To understand the pros and cons of monobloc and split air source heat pumps, and to find out more about how they differ, you can go to our article: Split Heat Pumps vs Monobloc Heat Pumps

Air source heat pump temperatures

Air to water heat pumps often come in 2 separate temperature ranges: low temperature and high temperature. It's important to know what each of these temperature types are as they could affect your installation costs.

Low temperature heat pumps

While traditional gas boilers will heat the water in a central heating system to temperatures of around 80°C to ensure the radiators around the property are providing ample heat. Low temperature air source heat pumps are only capable of heating radiators to a temperature of around 60°C. Due to the lower maximum temperature these heat pumps are capable of producing, more heated surface area is required to keep a property warm. This means you will need bigger radiators or underfloor heating to truly benefit from the installation of a low temperature heat pump.

High temperature heat pumps

Generally, high temperature air source heat pumps are capable of heating the water in a central heating system to around 75°C – 80°C. This is more in line with the temperatures provided by gas boilers. This makes them easier to integrate into an existing traditional heating system, but they do require more power to run.

For an in depth comparison and explanation of different temperature levels in heat pumps, check out our Low Temperature vs High Temperature Air Source Heat Pumps article.

The benefits & disadvantages of an air source heat pump

There are many benefits to getting an air source heat pump installed at your property, but there are some disadvantages too. To help you make the right decision for your home, we created the article: Air Source Heat Pumps vs Gas Boilers. This covers the advantages and disadvantages of each technology, cost comparisons and things you will need to consider when getting either heating solution installed.

Finding an Installer

As air source heat pumps are a relatively new technology, you may find it harder to find a heating engineer in your area that's well versed with installing them. More and more heating engineers are starting to adopt air source heat pumps as a heating solution they will install, but it may not be clear where to find them.
Fortunately, this is something we can help with. Simply click the link below and we'll find you up to 3 quotes from air source trained heating engineers in your area.



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Adam Cherry

About the author

Adam Cherry

Adam is our resident home heating expert. His experience and advice has helped millions of customers improve the efficiency of their homes and save money.

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