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What is an air source heat pump and how do they work?

An air source heat pump is a low-carbon heat source that works by extracting heat energy from the air in order to warm your home and provide hot water.
Aside from their eco-credentials, an air source heat pump system is also very efficient.

For every unit of energy it uses to extract heat from the air, it typically outputs three times more as heat, meaning air source heat pump efficiency is around 300%!

Air source heat pump benefits include:

  • Low carbon, environmentally-friendly heat source
  • Highly efficient, transferring around three times more energy into a home as heat than it uses to extract it from the air
  • Eligible for the government Boiler Upgrade Scheme
  • Little outdoor space required, meaning an air source heat pump system is suitable for most urban properties
What is a Heat Pump and how do they work


An air source heat pump collects energy from the air, even at low temperatures.

1. Evaporator

The energy is absorbed from the air to the refrigerant in the evaporator.

This process increases the temperature of the refrigerant, changing it from a liquid to a vapour.

2. Compressor

The vapour is compressed by an electrically driven compressor, increasing its temperature.

3. Condenser

The condenser releases this heat energy into the water used in your heating and hot water system.

4. Expansion Valve

The cooled refrigerant turns back into a liquid and the process starts again.

How do air source heat pumps work in winter?

Air source heat pumps contain refrigerant circuits that compress gas to create heat. This refrigerant is in liquid form until the heat is absorbed and ‘boils’ to become gas. This gas is then compressed to become hot and the heat is transferred for use in the property.

The ‘boiling’ of this liquid can happen from -50°C. Therefore air source heat pumps work in temperatures as low at -20°C. As temperatures in the UK rarely reach these drastic lows, air source heat pumps are a viable option for many projects.

As part of our design process, Nu-Heat will also take into consideration the average temperature of your projects location to give you reassurance that your heat pump will be effective.

How do air source heat pumps work in winter?

Watch Our Heat Pump and Underfloor Heating Masterclass

Learn the essentials with our resident expert Jo Snell, Self-Build Manager at Nu-Heat.

Watch masterclass

Heat Pump and Underfloor Heating Masterclass

Can air source heat pumps work with radiators?

Yes, air source heat pumps work with radiators, and you may choose to use radiators to minimise disruption within your home or to save on costs. However there are a few considerations to take into account before you make this decision.

For an air source heat pump to work with radiators, it’s worth bearing in mind that they will need to be sized in line with the lower water flow temperatures associated with heat pumps. This means they are generally twice the size of those used with a gas or oil boiler.

Find out more with our blog post on UFH vs Radiators.

Radiator pros and cons

Can air source heat pumps work with underfloor heating?

Yes, air source heat pumps are a great option to pair with underfloor heating!

Air source heat pumps are at their most efficient when producing low temperatures over a sustained period of time. Underfloor heating systems require lower flow temperatures, at around 40-50°C, to be circulated across the entire floor area to provide heat, making an UFH system the preferred pairing option for an air source heat pump.

In comparison, a traditional radiator system needs to use water around 70-80°C in order to heat the rooms using a much smaller surface area.

What is underfloor heating?

How an air source heat pump works FAQs

Does an ASHP work when it’s below freezing?

Yes, air source heat pumps can work in temperatures as low as -20°C, and when you work with Nu-Heat, we’ll take the average temperature of the project’s location into account during the design process to ensure you are getting the most out of your heat pump.

Can I install an ASHP in an existing property?

Yes, as long as the property is well insulated an air source heat pump can be installed in a whole range of different scenarios!

Can I use an ASHP in an uninsulated property?

No, due to the low flow temperatures utilised by air source heat pumps, they are not suitable for use in poorly insulated properties. Use our heat pump suitability tool to see if a heat pump is right for your project.

How do I control my air source heat pump?

Nu-Heat will always design the system to perform at its optimum level, and as part of the commissioning procedure, we will also ensure everything is perfectly set up, so there should be no need for homeowners to make additional changes to settings. All that is required is an annual service.

Will an air source heat pump heat my domestic hot water?

Yes, an air source heat pump supplied by Nu-Heat will be designed to take care of all the heating needs of your property, including domestic hot water. In fact, a part of our detailed design service is dedicated to ensuring accurate sizing of the domestic hot water cylinder.

Will my house be warm?

Yes, a correctly designed and installed heat pump will meet all the heating needs of a property. However,  as heat pumps work with a much lower flow temperature than boiler systems, you won’t get the same intense heat that you may be used to with a boiler and radiator system. Instead, heat pumps are paired with larger heat emitters such as large radiators or UFH that emit a low level of heat consistently.

Considering a heat pump for your project?

For expert advice on heat pumps and underfloor heating, contact us today.