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.
HI GreenAge
Just want to say thanks for keeping us up to date about green initiatives but i think you are missing the point of the heat pump technology. They are not meant to be cheaper, just greener. They make sense for people with solar installations with excess power. I have a system with 8kwh average output and use around 3kwh. It would make sense to use the 5kwh of spare power to run a heatpump but I’m happy for it to go to someone else’s smartphone if it saves gas and coal doing the job.
I think heat pumps should be priority 3 for the government schemes, 1 being solar panels for homes and 2 being electric cars.
They are coming but we need the green supply before we increase the demand.
Most boilers are around 24kw
So one hour of gas heating is 7p x 24 = £1.68
Air source geat pump system runs at 3kw , so 28p x 3 = 84p
Soooo, that’s both at 100% efficiency.
Please, if you are going to do articles like this, please do give all the information.
Hello Me
Your assumptions miss the point a bit, too. Gas central heating can be put on for 1-2 hours in the morning then 1-2 hours in the evening, so taking worst case at 24 kWh gas boiler consumption over 4 hours/day then this equates to 96 kWh/day for heating at 7p/kWh = £6.72 paid for gas./day
A comparible sized heat pump drawing 3 kWh needs to run all day during the colder months, may not heat the house to the desired temp if only running at CoP 1.5 (4.5 kWh heat supplied) and needs to shut down to defrost during the coldest periods of the day so often needs a backup or will let the house go cold. 3 kWh x 24 hrs x 28p = £20.16 electrcity/day provided no fall back temp at night is set (if the heat pump does indeed reach full house temp).
Until gas prices reach electricity prices like James says below, there’s not much point for older draughty home, but what would be the chance that gas prices will reach electricity prices in the future if the government introduces a carbon tax and removes fossil fuel subsidies? Then it would absolutely make sense, but we’ll all be paying sky high energy prices well in to the future unless we can afford a large enough solar array installation and huge insulation upgrades and high heat pump installation costs simultaneously.
a typical UK home requires 6-8kW for heating, the boiler won’t run at 24kW most of the time (otherwise you would need a heatpump of 8kW to match assuming a COP of 3) so your figure for it is really 7px8=56p or cheaper than the heatpump. But, as others have said, heatpumps aren’t about cost but being green (if the soure of the eletricity is).
Nah, don’t worry about the climate, count the cost!
Missing the point really – Use of electric heating such as via heat pumps is not about saving money (although it does) its about CO2 emissions, as time goes on more electricity is going to come from renewables or nuclear. So the argument about electricity using fossil fuels for its generation is only a short lived one (same argument applies to electric cars) its part of a large plan of change to reduce dependency on fossil fuels and as a side benefit cost and energy security.
Using heat pumps might well push us to insulate our homes better, which is no bad thing!
Hi Brian, I agree to a point – however with any intermittent energy source installed, its capacity needs to be matched with a source that can defo be turned on / off (e.g. Gas power plant). So I would actually say it is pretty relevant. There are also transmission losses to think about – Burning gas in your home is more efficient than using electricity made from gas delivered to your home.
Also the cost of electricity is so much higher than the cost of gas. Until they reach parity then the whole decision is a bit of a no brainer.
Your final point in terms of having to insulate our homes better is absolutely true!!
Thanks for this well written & concise article, it echoes my instinctive musings on the matter.
Nobody is going to run air source heat pumps when it is warm. It seems self evident that getting heat from cold air will require a lot of power, which perhaps could be used more directly. I mean at what point do we just have direct electrical panel heaters instead for example?
I really think widespread adoption of this technology will be a huge mistake. I also worry about people being urged to “upgrade” in their stone built solid wall houses, insulating them but not allowing for ventilation…there are going to be so many moisture problems.
And how constantly will these units have to run when it’s cold? They will be a noise nuisance I’m sure, as are air-con units. They are just as ugly too. Even if all the power used is renewable or nuclear, they could still have negative effects on our standard of living by aesthetics & noise. Huge radiators for example, & complete overhaul of plumbing.
Efficiency & insulation, & maybe running a home a little cooler & using a blanket seem like sensible steps.
An inaccurate article. The consensus of science, world governments and the IPCC state CO2 is causing climate change and an unlivable world
The Government need to start insulation grants again including for solid walls. Evidently there are no bungs forthcoming for them so it won’t happen
Heat Pumps Definitely ARE the answer.
I think your article on the ASHP is a bit disingenuous, The fact that 85% use gas is neither her nor there, we all have to start the journey to stop burning fossil fuels, and move to electric,… clean electric. If we do move to electric, then a large proportion of that can be made with renewable and nuclear. even if oil or gas is burned centrally, it will make up perhaps around (only) 50% of the overall electrical energy suppled to customers. Secondly, even if the heat pump efficiency is (only) 1.5 it is still MUCH better than 0.9 from a well setup gas or oil boiler. So a gas boiler producing 1kWh of energy will burn 1.11kWh of fossil (gas),.. a (1.5 COP) heat pump will use 0.66kWh of electrical energy to produce 1kWh of heat, of which only 50% was fossil, so only using 0.33kWh of fossil. the rest (0.33kWh) was nuclear, wind, solar. Using 1.1kWh or 0.33kWh of fossil to create 1kWh of heat,… which is better? Often at night the UK turns off 50% of our wind generation, as there is no demand for it! Heat pumps could be using this energy.