If you’re interested in upgrading your home’s central heating to an air source heat pump, you’ll no doubt have asked yourself how much does an air source heat pump cost to run?

In this article we’ll take your through the steps necessary to calculate this amount for yourself. We’ll also been comparing the air source heat pump to electric and gas central heating.

Calculating the cost of running an air source heat pump is not as simple as with fossil fuels such as a gas boiler. The reason for this is twofold: Firstly an air source heat pump produces more energy in heating than in uses in electricity. Secondly a heat pump’s efficiency changes as the external temperature changes.

To deal with the first issue – the fact that an air source heat pump creates more energy than it uses – we must simply calculate the cost based on the energy used to create this renewable energy. A simpler way to understand this is to think of a heat pump as a device which does not create heat, but rather *transfers* heat. Using heat transfer technology, an air source heat pump will take atmospheric heat and transfer this to a home’s heating and hot water. We therefore need to calculate the cost of transferring this heat.

Secondly an air source heat pump’s efficiency alters throughout the year. During warmer months a heat pump is more efficient, this is because there is greater atmospheric warmth to transfer. Although efficiency decreases during colder months when this atmospheric heat decreases. This efficiency of heat transfer is known as the Coefficient Of Performance (COP). A COP of 2 means that an air source heat pump will create (or transfer) twice as much energy as it requires in electricity to run. So in numbers, the heat pump will create 2kW of energy for each 1kW used. As we mentioned previously, this COP will alter over the year. We therefore need an average, this is available in the form of the Seasonal Performance Factor (SPF).

Air source heat pumps have an SPF for heating of 3 (they’ll create 3kW of heating for each 1kW of electricity used) and for hot water 2.5. These are the magic numbers we need to calculate how much it will cost to run an air source heat pump.

The next stage is to work-out how much heating our home will require. A largish four bedroom detached well insulated home may use 16,800 kW hours of heat energy per year. To generate this much heat, the heat pump will need to use only one third of this – remember that the heat pump transfers three times as much energy as it uses. So the heat pump will need 5,600 kW hours of electricity (16,800/3) to run. Let’s assume you’re paying 14p per kW of electricity – you’ll need to multiply 5,600 by 14p to get your annual heat energy usage. This equals £784 per year to run the heat pump providing all your home’s heating.

Hot water still needs to be calculated. It’s likely this same home will need 2,000 kW hours of energy per year to heat their home. This time the SPF is 2.5, so we divide 2,000 by 2.5, this equals 800 kW hours. Multiply by 14p gives a total cost of £112 per year.

Therefore the total cost to run an air source heat pump per year is £896.

Let’s quickly compare this to a couple of alternatives. If you’d used electricity you’d need to multiply you total kW hours for both heating and water by 14p (since these are no factors involved) – this would cost £2,632.

If you’re using gas the cost per kW of energy is generally around 5.4p, this would cost £1,015.2.

Hopefully this blog post has provided you with the tools to calculate for yourself how much you can expect to save using an air source heat pump. Don’t forget to also take into account government incentives such as the Renewable Heat Premium Payment (RHPP) and the Renewable Heat Incentive (RHI).

Any thoughts? Well I’d love to hear about them in the comments section below