It is clear from Government policy, that they are intent on pushing electric heating in homes in the UK. This is despite 85% of us using gas central heating systems to provide the heating for our homes as well as hot water.
The Government is looking to ensure that from 2025, new build properties are not allowed to be built with gas central heating systems. They are instead favouring ‘green’ alternatives like air source heat pumps. On the face of it, it is not such a bad idea, as homes will no longer be burning gas to produce hot water for heating and cleaning – so homes will no longer be producing the carbon dioxide associated with burning fossil fuels which is thought to contribute to climate change.
For us though, there are two major issues.
Efficiency of ASHPs is much lower during Winter
The first is the efficiency of air source heat pumps. The Government feels heat pumps are game changing technologies as they are highly efficient – at times converting 1 unit of electricity into 4 or 5 units of useful heat (so 400 or 500% efficiency), while a gas boiler might be somewhere around 90 – 95% efficient.
On the face of it, that makes it look a no brainer. A very efficient heating system that produces no carbon dioxide. The issue is that the efficiency numbers often cited in the media are not annualised figures (i.e. an average efficiency over the course of a year). They are cherry picking the peak efficiency – which occurs when the air temperature is in excess of 20 degrees.
Air source heat pumps work by taking latent heat out the air, and transferring this into a refrigeration coolant. The coolant is then compressed using an electrical compressor which drives the temperature up, and then a heat exchanger takes the heat from the coolant and transfers it to the hot water within a heating system. Regardless of the air temperature outside of the property, the coolant typically can get to the temperature required to run a heating system – but it just takes a load more electricity as the compressor needs to work that much harder when the weather is cooler.
It is true there is some heat in the air even in extremely low temperatures, however in order to drive the temperature of the coolant up to a useful level, the compressor needs to work harder – and remember the compressor works on electricity. This brings the efficiency right down potentially to 150% efficiency. So, while in the summer, efficiency of the heat pump could well be in excess of 500% (i.e. one unit of electricity produces 5 units of useful heat), this is certainly not the case when the temperature outside is hovering around zero.
Now if you think of the times of year when you typically run a heating system, it is during the colder winter months. This means that when the weather is cooler, the compressor works harder, and your heat pump will be what we often describe as an electricity vampire.
What we are saying is that when you need the heating, air source heat pumps are working at their least efficient.
As of 16th March, gas and electricity prices are at unprecedented levels.
The cost of a unit of gas is approximately 7.5 pence per kWh.
The cost of a unit of electricity is approximately 28 pence per kWh
But typically the ratio has stayed the same even when prices were much lower – a unit of electricity is approximately 4 times the price of a unit of gas.
If you gas boiler is running at 95% efficiency, it is going to cost you right now about £0.07 per unit of useful heat.
In the winter, when the air source heat pump could be running at 150% efficiency, it is going to cost you £0.19 per unit of useful heat.
So no emissions in the home, but more than twice as expensive to run!
ASHPs are powered by electricity that may still come from burning gas
The other issue with electric heating systems is that while they produce no in home emissions, most of our power still comes from gas power plants. So, it is likely that gas was burnt to produce the electricity needed to run the air source heat pump anyway!
Obviously there has been huge investment into renewables like wind turbines, but if the wind doesn’t blow, much of our power still comes from fossil fuels.
I think there are a few points worth caveating though. Firstly, ground source heat pumps are a different story. They have a very similar efficiency all year round – approx. 450%. However, they are extremely expensive to install.
If you do go for a heat pump, it does infer that your house is sufficiently insulated (their working temperatures are far lower than gas boilers), so that in itself will see you have lower energy bills that an uninsulated equivalent property.