Six things you'll only know if you have a heat pump

Richard Casson admits he was a little nervous when a mechanic arrived at his north London flat in May to replace his traditional gas boiler. He wasn’t coming to install a newer model but a heat pump, the low-carbon alternative being hailed by Boris Johnson as the forefront of Britain’s home heating revolution. Casson, who works as a fundraiser for Greenpeace, was obviously motivated by a desire to tackle climate change – but also, if he’s honest, by a simple fascination with new gadgets.

“With everything changing in terms of how we heat and power homes, it didn’t make sense to lock myself into getting a[nother] gas boiler,” says Casson, 38. “I wanted something new and exciting, [that would also] cut my carbon footprint.”

Casson’s heat pump is one of only about 200,000 in use in the UK (in contrast, 25 million homes use a gas boiler). Now, he looks like something of a visionary, as Johnson presses ahead with his net zero plans to end the installation of gas boilers altogether in the next 15 years. The Government this week announced a campaign to encourage homeowners in England and Wales to replace their gas boiler with a heat pump when their current boiler eventually breaks, with grants of £5,000 to help 90,000 households make the switch. But what will it actually involve? Here’s what you need to know...

1. How on earth do they work?

Heat pumps are usually affixed to an outside wall. Aided by a fan, they extract warmth from the outdoor air. This warm air causes a special refrigerant liquid inside the pump to evaporate, turning it into gas. That gas is then sent through an air compressor, increasing its pressure and making its temperature rise. This hot air is then blown straight into a home, or used to heat water which feeds radiators.

It works rather like a fridge in reverse, says Will Rivers, senior manager at the Carbon Trust consultancy. “A heat pump is taking a very large quantity of low-temperature heat [from outside the house], and then compressing it into a smaller volume of high-temperature heat. It might only be two degrees outside, but there is still energy in that air if you capture enough of it.” Manufacturers claim this process works in temperatures as low as -20C – although the colder it gets, the more energy the pump needs to function. There are also heat pumps that draw energy from the ground or water.

2. Will they cost more to run?

Experts say the average heat pump costs between £6,000 and £18,000, depending on the model installed and the size of a property. But this cost can be reduced by government grants. Casson paid £11,000 for a heat pump for his Finsbury Park flat – significantly pricier than gas boilers, which usually cost below £2,500 – some of which he will get back under the Government’s Domestic Renewable Heat Incentive scheme, which pays him about £1,000 a year for seven years. “It goes straight into my bank account.” The exact amount he can claim depends on the amount of fossil fuels his household previously used (the more carbon you are ‘taking out’ of the system by buying a heat pump, the more money you will receive).

Richard Brown, 57, an IT project manager, paid roughly £10,000 last February to replace his gas boiler with a heat pump at his four-bedroom detached house in Derby. He says it allows him to save between £300 and £400 a year on fuel costs.

Ministers claim their newly-announced £5,000 grants will make the cost of a heat pump comparable to that of a new gas boiler, although environmental groups claim the policy is not going far enough.

3. Will my home be colder?

Heat pumps heat the water in your house to a maximum of about 65C – significantly lower than it would reach under a traditional gas boiler (about 75C for water in radiators, and between 50C to 60C for the water in your kitchen and bathroom taps). This means they generally take longer to heat your home. Sceptics worry that heat pumps will leave them cold during winter, but Brown says he simply left the heat pump switched on “all the time”, rather than trying rapidly to warm everything up when arriving home from work. This allows his home to get just as warm as it would under a gas boiler, while still using much less carbon. “It keeps us perfectly warm,” he says.

Casson, too, says his initial concerns were unfounded. “You hear rumours, but I’ve found those things to be myths. You choose the temperature you want. We set ours at 50C, and it really comfortably gets to 50C. If we put our radiators and hot water on, we just never have any issues.”

4. Just how noisy are they?

Some worry that the whirring of the heat pump’s fan might prove noisy. But Casson says he cannot hear his fan when inside his flat (the fan is fitted to an exterior wall at the back of his block). “When the engineer switched it on for the first time, he was saying, ‘You won’t be able to hear this’. And I was thinking, ‘God, is he just saying that?’ And he turned it on, and I literally laughed out loud. You read all this stuff about it being noisy, but it’s really not.

Casson thinks heat pumps might “start to make noise over time”. But he says if that happens he can simply “put a bit of WD40 [lubricant] on the fan to sort it out” (his pump receives a free annual check-up as part of his payment deal).

Brown’s fan was installed on the outer wall of his kitchen. He says he can only hear it while standing in the garden. “It works hardest in winter, when you’re generally not using the garden anyway. Whereas in the summer, it’s off for most of the daytime.” Even on the rare occasions he’s in the garden in winter, the hum of the fan is little more than a “gentle background noise”, Brown says.

5. Are they tricky to use?

Even though he works for Greenpeace, Casson admits the technology behind heat pumps is “quite sophisticated, there are some parts I don’t really understand myself; I’m getting my head around it.” But after some “tinkering” with the settings to make his pump as cost-efficient as possible, he’s now getting the hang of it.

Meanwhile, Tom Jenane, a nutrition and fitness coach, admits he was “incredibly confused” when he moved into his rented flat and discovered his landlord had installed a heat pump instead of a boiler. “It was not previously mentioned by estate agents; they told me that it would save money on my monthly energy bills, so I should be happy about it. They mentioned that it utilises the soil outside in my garden to create the heat, but that’s as far as my knowledge goes in this area.”

But, Jenane adds: “The idea that I might be lowering my carbon footprint sounds good to me.”

6. Will we all have to have one soon?

“The Greenshirts of the Boiler Police are not going to kick in your door with their sandal-clad feet and seize, at carrot-point, your trusty old combi,” Johnson wrote in The Sun this week. But setting out his new green agenda today, he announced builders would be banned from fitting conventional gas boilers in new-build homes by 2025 and committed to the “ambition” of ending the sale of gas boilers in the UK from 2035.