Air source heat pumps essentially move heat into the home, utilising the energy in the outside air. During the process, they use a compressor to drive the temperature to a level sufficient to heat homes and provide hot water to the occupants.
Air source heat pumps run off electricity, and on the face of it, this should make their running costs very high – electricity is 15p / kWh, while a unit of mains gas is just 3.75p / kWh.
In fact though, they turn one unit of electricity into about 3.5 units of useful heat – this is what is known as the coefficient of performance. This means that they are actually producing hot water at about the same price as gas (because they are 350% efficient).
Now in the winter, when the air gets colder, it actually takes more energy to drive the temperature up. This reduces their efficiency to far lower than 3.5 – in fact, you may only get 2.5 units of useful heat for every unit of electricity at this time, while in the summer it might be 4.5 units of useful heat for every unit of electricity.
This seasonal fluctuation of the coefficient of performance does not make comparing heat pumps very easy. Instead we use the Season Performance Factor – this sort of averages the daily coefficient of performance over the year, which allows you to compare different models of air source heat pump.
However, this doesn’t reveal the cost profile of the running costs of a heat pump (i.e. it is more expensive to produce hot water in the winter when more is needed, while it is cheaper in the summer when hot water is not needed as much for heating!)
So are heat pumps worth it?
So based on the fact that air source heat pumps vary in efficiency through the year – are they worth installing?
Well – it depends! I know – not like us to sit on the fence, but let me explain why!
The key consideration with all heat pumps (ground source and air source) is that the hot water they produce is not as hot as a traditional boiler.
This means that for them to work effectively, your home needs to be very well insulated so as to minimise the heat loss out of the property. Therefore, if you live in a new property or your home has had wall / loft insulation then a heat pump should work really well.
If the house is not well insulated then the heat can very quickly escape out of the home. This reduces their efficiency, which quickly makes them a less than ideal heating solution.
Installing a heat pump may mean that you need to replace all of your existing radiators – since they will be undersized. This can really add to the installation process and cost, since radiators are not cheap to install.
The cost of heat pumps is falling!
Much like we have seen with solar PV panels over the last couple of years, economies of scale and improving technologies have led to a dramatic decrease in price and the same is happening with heat pumps.
We recently quoted an air source heat pump at £6,000 + VAT (at 5% instead of 20% for boilers). This, coupled with the generous Renewable Heat Incentive payment has suddenly made heat pumps far more attractive as an investment opportunity.
This is especially the case if you are living off mains gas, since the cost of alternative fuels like LPG, heating oil and even electricity (if you use electric convection heating for example) is very costly. In this situation, installing a heat pump, provided you have the available funds, should really be a no brainer.
If you have mains gas, then to be honest the savings are going to be negligible by replacing your existing boiler central heating system with a heat pump so unless you want to lower your carbon footprint then we would advise you to stick with what you have got!