How to cut your energy bills by 30 per cent with a heat pump

News that energy bills are set to rise by 10 per cent from October has brought a distinctly wintry chill to the last of the summer sun. Who wouldn’t welcome a 30 per cent cut in bills now? But is ripping out the gas boiler and replacing it with a heat pump feasible for those of us with normal, draughty British homes — or is it really only for those with new-build Grand Design-style properties?
The presenter Kevin McCloud has seen a lot of heat pumps in those new-builds. He has one in his own house too. Yet the heat pump that “really points to the future”, as he puts it, is in a bog-standard three-bedroom 1960s semi in Peacehaven, East Sussex. It is compelling, says McCloud, who went to see it after it won a Heat Pump Possible award, precisely because it is in such an ordinary home.
Here, Luke Sheppard and Isabel Gilles have done a straight swap from a gas boiler to an air source heat pump. They did not do any messy work to fit extra insulation, pipework or underfloor heating. The installation took a few days in early 2023 and cost them about £1,000, on top of a £5,000 government grant. This would now be totally covered by the grant which has increased to £7,500.
Last winter, after the refit, their semi was as warm as it was with the boiler. Their boys, aged four and seven, still splash around in a hot bath every night. “I’ve not noticed a difference,” Gilles says. Best of all, their annual heating and hot water bill has fallen by almost a third.
The family’s heat pump system shows how most British families can switch to clean heating without pushing up energy bills. About 90 per cent of UK homes have carbon-emitting gas or oil boilers. Less than 1 per cent have heat pumps. This proportion must increase to 10 per cent by 2030 for Britain to hit its net-zero targets, according to the Climate Change Committee (CCC), which advises the government.
The biggest problem is that electricity, at 22.36p per kWh (rising to 24.50p per kWh from October 1) in the UK, costs four times as much as gas, at 5.48p per kWh (rising to 6.24p per kWh). It means a heat pump is more expensive to run than a gas boiler — unless your heat pump installation is highly efficient.
The secret lies in a number called the Scop (seasonal coefficient of performance). The Sheppard family’s gas boiler had a Scop of 0.92: for every unit of energy it used, the boiler produced 0.92 units of heat. That is normal for a gas boiler.
Heat pumps are much more efficient than gas boilers. The heat pumps fitted in 742 homes as part of a 2021 government pilot had an average Scop of 2.8 — meaning the machines multiplied one unit of energy into 2.8 units of heat. But because electricity costs four times as much as gas, you need a heat pump Scop of 4 to break even with a gas boiler. Anything above that will cut your energy bills.
Sheppard, a self-confessed heat geek who runs Optimus Heating, tinkered with his family’s heat pump system until he got a remarkable Scop of 5.2. “That’s where I get my savings from,” he says.
Heat pumps harness “a beautifully simple piece of science”, says Bean Beanland, the director of growth and external affairs at the Heat Pump Federation. “You can’t compress a solid, you can’t compress a liquid, but you can compress a gas. And when you compress a gas, it gets hot.” If you pump a tyre and put your thumb over the valve, it feels hot, he says. “That’s gas compression.” The same technology powers your fridge, freezer and car air conditioning, Beanland adds. “Most of us have never known life without a heat pump.”
• A high-temperature heat pump was a no-brainer for us
However, heating your home efficiently with a heat pump is not that simple. The whole system has to be correctly designed and fitted for that specific property, otherwise you’ll end up with a sky-high electricity bill, a cold home and a “very noisy” heat pump that has to work too hard, Sheppard says.
Over the past two or three decades installers have generally lost the skill to handle heating systems properly. “There was no need to. You could fit a combi boiler on the wall and it worked in any scenario. Standards didn’t need to be high,” says Adam Chapman, the co-founder of the Heat Geek network, which has trained 2,000 heat pump engineers (including Sheppard).
“No one cared about the efficiency of the buildings,” Beanland adds. “Because gas was so cheap it didn’t matter.”
However, for heat pumps, “the skill and experience of the installer is critical to success. It’s more about the quality of the installation than it is about the machine,” Beanland says.
Chapman agrees. “Do heat pumps work? The answer is yes. That’s why they’re used all over the world. Why they look like they haven’t worked is because a lot of heating engineers weren’t applying it the right way.”
The right way starts by calculating how fast your home loses heat on the coldest winter’s day. The heat pump system must be designed to put heat back in at the same rate, balancing out the heat loss to keep rooms at 21C when it is minus 3C outside. “If you’re getting a heat pump installed and someone hasn’t measured every room, every window, every door, to work out how much power your home needs, they’ve just guessed the heat pump size. That is the biggest mistake in installations,” Chapman says.
• ‘Our council is stopping us from insulating our home’
Sheppard worked out that his “very standard” semi lost 4.5kW of heat per hour on a minus 3C day. It has minimal insulation levels, with cavity walls filled years ago, 20cm of loft insulation (below the recommended level of 27cm) and uninsulated floor voids, he says. “I wanted to show that if you put a bit of science behind what you do, you can absolutely make these things work much more efficiently than running gas boilers.”
Next he worked out how to reduce the flow temperature of the water inside the pipes and radiators to 35C, while still heating the house to 21C on a minus 3C day. The lower the flow temperature of a heat pump, the less energy it uses — and the cheaper it is to run.
Chapman explains: “The heat pump will just trickle in the heat gently, rather than on full blast. It’s the same as a car: if you drive more slowly and evenly you use less fuel but you still get to your destination.”
A gas boiler has a typical flow temperature of 70C. To get the same comfort level with a heat pump running at 35C, you need bigger radiators. Sheppard replaced five slim radiators with larger double-panel ones, costing about £1,000. He combined that with the smallest heat pump on the market, a 3.5kW Vaillant aroTHERM plus.
The last piece of the puzzle is what is known as “weather compensation”, which increases the flow temperature when it’s cold outside but decreases it as it gets warmer. “It’s like when you had no thermostat in the house: you used to turn up the boiler on the boiler dial itself when it was cold, and turn it down again when it was spring,” Chapman says. Now a smart controller — like a Vaillant SensoCOMFORT, which Sheppard fitted in his living room — can move the dial for you.
Sheppard’s heat pump kit cost about £5,000, covered by a £5,000 grant from the government’s boiler upgrade scheme. He had no labour costs because he did the work himself.
Don’t fit gadgets such as buffers, zone controls or optimisers, Chapman says. “It’s normally a gimmick that nearly always lowers efficiency. The way we get the highest efficiency is by keeping the system as simple as possible. Often that works out cheaper to install.” Because Sheppard’s heat pump system is so efficient, his family’s heating and hot water bill has fallen by 29 per cent to £350 a year, compared with running a gas boiler at current energy prices (£455 a year). The annual saving of £105 will repay their capital investment within nine and a half years.
“Most homeowners want to save carbon, but they won’t pay additional [energy bills] to save carbon. It has to pay back in some kind of way,” Chapman says. Heat Geek has a calculator that estimates the installation costs and energy savings for a heat pump in your home. For a rough indication of whether or not a heat pump would suit your property, try the government’s online checker (heat-pump-check. service.gov.uk).
If installation is efficient enough to make a heat pump cheaper to run than a gas boiler, the continuing savings can formally be used to pay off the upfront costs. Financing based on these savings is about to be unleashed on the mass market, Chapman says. “It’s the thing that we’re all talking about.”
The Sheppard family’s heat pump was one of 60,000 fitted in UK homes last year. Uptake has increased after grants rose from £5,000 to £7,500 last October. Monthly applications to the scheme have since doubled compared with a year ago. Yet Britain still lags far behind its European counterparts.
Take the Netherlands, where nine in ten homes were gas-heated — a similar proportion as in the UK. Yet Dutch heat pump uptake is now 20 times higher than in Britain, aided by financial incentives and an electricity price that is only 1.5 to 2.5 times higher than gas, according to the CCC.
The committee urged the government to make electricity cheaper to lower heat pump running costs. Policy levies add up to £300 to the average annual energy bill of families with electric heating, according to research by the energy analysts Cornwall Insight for the MCS Charitable Foundation.
Planning barriers to heat pumps should also be scrapped, the CCC says. You still need planning permission to place a heat pump within one metre of your garden fence.
There is a way to go until we can fit heat pumps easily in our homes but Sheppard and Gilles have shown what is possible.
1. Do a heat loss survey2. Correctly size the heat pump to balance out heat loss3. Fit bigger radiators where possible 4. Consider upgrading insulation where cost effective5. Add weather compensation smart controls6. Leave out zoning gadgets