The average UK home loses heat at 2.5 kW per degree of temperature difference, a figure that has barely budged since the 1970s. For the 12 million households living in pre-1930s solid-wall properties, that number is closer to 4 kW. For years, the official line has been simple: insulate first, then electrify. Mitsubishi Electric’s new white paper on high temperature heat pumps challenges that orthodoxy head-on.
As reported by Installer Online, Mitsubishi Electric’s white paper argues that high temperature heat pumps, which deliver flow temperatures of 65–80°C, can replace gas boilers in existing homes without the full insulation overhaul typically demanded by standard heat pumps. For homeowners who have been quoted £15,000 for a standard heat pump plus £20,000 for external wall insulation, that is a material difference.
Who qualifies, and who doesn’t
The white paper targets the roughly 40% of UK homes with EPC ratings of D or below. These are the properties where standard heat pumps struggle because the building fabric leaks heat faster than a low-temperature system can replace it. High temperature models solve this by running hotter water through existing radiators, often the same ones already fitted.
But the catch is efficiency. A standard heat pump operates at a coefficient of performance (CoP) of 3.0–4.0, meaning it produces three to four units of heat for every unit of electricity. High temperature models typically drop to 2.0–2.5 CoP. That means higher running costs: roughly £200–£300 more per year on a typical 3-bed semi using 12,000 kWh of heat, according to Energy Saving Trust data. The trade-off is a lower upfront cost, typically £8,000–£12,000 installed versus £12,000–£18,000 for a standard heat pump plus insulation.
What it costs a typical 3-bed semi
For a homeowner in a 1930s semi-detached with cavity walls and double glazing, the numbers look like this:
- Standard heat pump (8 kW): £12,000 installed, plus £5,000 for cavity wall and loft insulation top-up. Total: £17,000. Running cost: £700/year at current electricity prices.
- High temperature heat pump (8 kW): £10,000 installed, no fabric upgrades. Running cost: £950/year.
The Boiler Upgrade Scheme offers £7,500 off either option. After grant, the standard route costs £9,500 upfront; the high temperature route costs £2,500. The payback period for the cheaper upfront option is roughly four years on the running cost difference, and that assumes electricity prices stay where they are. Ofgem’s price cap for October 2025 shows electricity at 27.5p/kWh, with gas at 6.5p/kWh. Even at a CoP of 2.5, high temperature heat pumps beat gas on cost per kWh of heat delivered (11p vs 6.5p? No, 27.5p / 2.5 = 11p, which is higher than gas). The white paper acknowledges this and argues that as the grid decarbonises, electricity prices should fall relative to gas.
EPC impact and grant eligibility
The EPC calculation rewards heat pumps heavily. Replacing an old gas boiler (band D) with a high temperature heat pump can lift a property from band D to band C, a gain of 10–15 points, because the heat pump’s efficiency is scored higher than the boiler’s. The Sustainable Energy Association confirmed to me last month that high temperature heat pumps qualify for the Boiler Upgrade Scheme as long as they meet the minimum efficiency requirements (a CoP of at least 2.5 at 55°C flow temperature).
Yet the white paper stops short of saying every home is suitable. Homes with single glazing or uninsulated solid walls will still see high running costs. The Mitsubishi document recommends a minimum of loft insulation and draught-proofing before installation. That is not a full fabric overhaul, but it is not zero work either.
What this means for your next decision
If you are a homeowner with a gas boiler older than 10 years and an EPC rating of D or below, the high temperature heat pump route is worth a serious look. The lower upfront cost, especially with the £7,500 grant, makes it accessible to more households. But you should model the running costs carefully. Use the Energy Saving Trust’s heat pump calculator online, input your property’s heat loss, and compare against your current gas bill. If the annual running cost difference is under £200, the simpler install probably wins. If it is over £400, you may want to insulate first.
Applications for the Boiler Upgrade Scheme close on 31 March 2027. Installers are reporting lead times of 8–12 weeks for high temperature models. The window is open, but not forever.
Frequently Asked Questions
Yes, in most cases. High temperature heat pumps deliver water at 65–80°C, similar to a gas boiler, so they work with existing radiators and pipework. Your installer should check radiator sizing during the survey to ensure adequate heat output.
It depends on your electricity tariff and the heat pump's efficiency. At a CoP of 2.5 and current electricity prices, the cost per kWh of heat is roughly 11p versus 6.5p for gas. However, if you have a time-of-use tariff or solar panels, the gap narrows. The main saving is upfront, a lower install cost and the £7,500 grant.
