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Air source heat pumps work by absorbing the heat from the outside air and use it to heat hot water, radiators and under floor heating.

  • So how is there enough heat in the outside air to heat my home?

A common misconception is that because water has a boiling temperature of 100°C, then all liquids do. However, R410a, which is found in many air source heat pumps, has a boiling temperature of -48.5°C meaning that even when temperatures are as low as -15°C, heat pumps are still able to get heat from the air.

  • Here is a little diagram that explains it all.
  1. Ambient air passes over the evaporator; the refrigerant boils and evaporates at low temperatures.
  2. Vapour is channelled into the compressor. Pressure and temperature is increased.
  3. Warm, high-pressure vapour enters the heat exchanger producing heat for the water/heating.
  4. Condensed vapour returns to liquid and passes through the expansion valve reducing pressure and temperature.
  5. The cycle repeats.

Now we understand how they work, we can understand how they are more efficient that other heating systems.

In comparison to gas, a gas boiler will produce less than 1 kW of heat energy for every kW of gas consumed. A heat pump on the other hand harvests renewable energy from the outdoor air so will produce 3 or more kW of heat energy for every kW of electricity consumed.

When compared to oil, not only are they much more efficient create lower carbon emissions and have considerably lower operating costs, there is no need for fuel deliveries or having to worry about rising oil prices.

The key to getting the most from your air source heat pump starts at the very beginning. Insulation is important; a minimum of 300 mm loft insulation, heat rises after all.

If your home does not already have double-glazing, it would be worth updating your windows to eliminate any draughts.

There is also a lot of heat lost through walls so find out how your walls are insulated and if you can make any improvements.

When you are ready to start thinking about installation, always use an accredited installer to design your system, whether that’s for a new build property or a retrofit. Discuss the best options for the property including radiators and under floor heating.

  • Always use accredited installers to complete the installation, it might seem straightforward to install but there is much more to it than a few copper pipes and a bit of cable.
  • Speak to your installer about what works for you; is the house occupied all day so you need the heating on throughout the day or are you up early so need the house to be warm for your morning routine.
  • Decide if you need hot water for the kids evening baths as well as hot water first thing in the morning.

Programming the system for your needs means, you are not wasting energy when you don’t need to.


It can be trial and error until you find the right fit or your circumstances might change, you can easily adapt your system to suit you and most can be easily monitored/changed through an app on your smart phone.

Finally, keep in touch with your installer and arrange regular servicing. As with all things mechanical, they need the once over every year to make sure they are running smoothly. Planned maintenance can help detect issues with the system, which may prevent any downtime and loss of heating or hot water.

Mitsubishi Electric have this infographic, which shows the ‘evolution’ of our heating systems.

Therefore, whilst heat pumps are an investment, long term they are much more environmentally friendly than the alternatives, I believe gas has an expiry date. Air source heat pumps are not just the future; they are for the here and now.

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