The honest version of the heat pump conversation in 2026 sounds different from the version most of the industry is having.
Yes, heat pumps work in UK weather. Yes, the Boiler Upgrade Scheme genuinely closes most of the cost gap with a gas boiler. Yes, the running costs on Octopus Cosy can beat gas. But the conditions for it to work well are real, and the conditions for it to be a misery are equally real. The whole equation depends on three variables your gas boiler doesn't care about: insulation, radiator sizing, and how long you're going to live in the house.
If you're getting any of those wrong, the heat pump won't fix them.
How a heat pump actually heats a UK house
Gas boilers send 60-80°C water around your radiators. Heat pumps send 40-55°C water. That's the single most important fact about how they work, because it explains everything that follows.
Lower flow temperature means:
- The radiator surface is cooler, so it emits less heat per square metre. To deliver the same room warmth, you need bigger radiators or underfloor heating.
- The system runs continuously at low temperature rather than cycling on and off in 30-minute bursts. This is fine if you're home all day; it's a behaviour change if you're used to "boiler on at 5pm, off at 10pm."
- Heat loss from a poorly insulated room exceeds the heat input from a low-temperature radiator, and the room never reaches setpoint. This is what people mean when they say "heat pumps don't work in old houses." It's not the temperature outside; it's the U-values of the walls.
The performance metric is COP (Coefficient of Performance). A modern heat pump in a well-insulated UK house averages COP 3-4 across a year, meaning 1 kWh of electricity in produces 3-4 kWh of heat out. In a draughty Edwardian terrace with single-glazed windows and no wall insulation, you'll see COP 2-2.5 if you're lucky, and the running cost balloons accordingly.
What you'll actually pay
The 2026 spread for an MCS-certified installation, after the £7,500 Boiler Upgrade Scheme grant:
| System size | Gross install | Net after BUS grant |
|---|---|---|
| 5kW (small home) | £9,000-£13,000 | £1,500-£5,500 |
| 8kW (mid 3-bed) | £11,000-£16,000 | £3,500-£8,500 |
| 12kW (large home) | £14,000-£20,000 | £6,500-£12,500 |
Compare those net numbers to a like-for-like gas boiler replacement at £2,500-£4,500 and the picture's no longer wildly skewed against the heat pump. For a typical 3-bed semi, a heat pump installation costs roughly £1,500-£4,000 more than a new gas boiler after the grant. Recouped over a decade of marginally cheaper running costs, that's a defensible decision.
The variables that move your install cost:
- Heat pump brand: Daikin Altherma and Mitsubishi Ecodan are the volume leaders; Vaillant aroTHERM and Worcester Bosch Greensource sit in similar territory. Quality is broadly equivalent at the domestic level.
- Existing radiators: most older radiators are sized for 70°C flow and won't deliver enough heat at 50°C. Expect to replace 2-6 radiators in a typical install. Budget £100-£250 each plus fitting.
- Hot water cylinder: combi-boiler households don't have one, so this is a new install. £600-£1,500 plus the airing-cupboard space it takes up.
- Electrical work: heat pumps draw 3-5kW, which most existing consumer units can handle, but you might need a fuse upgrade or a dedicated circuit. £200-£600.
What the running cost actually looks like
The honest comparison for a typical UK 3-bed home with reasonable insulation:
| Heating | Annual cost |
|---|---|
| Pre-condensing gas boiler, no insulation upgrades | £1,500-£2,500 |
| Modern condensing gas boiler, well-insulated | £900-£1,400 |
| Heat pump, standard electricity tariff | £1,400-£2,200 |
| Heat pump, Octopus Cosy tariff | £700-£1,200 |
The two relevant comparisons are: modern gas boiler at £900-£1,400 versus heat pump on Cosy at £700-£1,200. The heat pump wins, but only modestly, and only on the right tariff. Without Octopus Cosy or an equivalent time-of-use tariff, the heat pump is roughly cost-neutral with gas. With Cosy, it's £200-£500 a year cheaper.
That's not a transformative saving. The economic case for heat pumps in 2026 isn't really about cheaper running costs; it's about future-proofing against gas price volatility and complying with policies that are heading toward gas boiler phase-out, plus the modest grant-supported install premium being recouped over a decade.
If you're motivated by carbon reduction rather than economics, the case is stronger; UK grid electricity is around 60-70% lower-carbon per kWh of heat than mains gas in 2026, and getting cleaner each year.
The insulation question
Heat pumps in poorly insulated houses have a reputation problem because they genuinely don't work well there. The solution isn't to abandon the heat pump idea; it's to fix the insulation first and then come back to the heat pump conversation.
The order I'd put it in for a typical UK home considering both:
- Loft insulation to 270-300mm. Cheap (£300-£600 DIY, £600-£1,200 installed), high payback regardless of heating system. If your loft has less than 200mm, do this before anything else.
- Cavity wall insulation if applicable. £400-£1,500 typical, useful for any heating system.
- Draught-proofing windows and doors. Cheap and high-impact.
- Window replacement to double or triple glazing, if currently single. Expensive but a meaningful change in how the house holds heat.
- Then quote the heat pump.
Some installers will fit a heat pump on a poorly insulated house and the system will technically work, but you'll be running at COP 2 or worse, which means electricity bills 30-50% higher than projected. The Boiler Upgrade Scheme funds insulation surveys; use that.
What we'd actually do, sequenced
For a UK homeowner thinking about heat pumps:
Stage one is the survey. Find an MCS-certified installer who'll do a heat-loss calculation for your specific house, room by room. This is what determines the heat pump size and which radiators need upgrading. Beware quotes that don't include a heat-loss calc; they're guessing.
Stage two is comparing apples to apples. Get three heat pump quotes and one or two gas boiler quotes. Look at the all-in install cost, the radiator upgrades, the cylinder, the electrical work, and the projected running costs based on your actual energy use last winter. Most heat pump quotes I've seen include the BUS grant deduction; check the gross figure isn't being hidden.
Stage three is the tariff. The heat pump only beats modern gas on Octopus Cosy or similar time-of-use tariff. Switch to Cosy in parallel with the install, not "later." If your supplier doesn't offer a heat-pump-friendly tariff, switch to one that does.
Stage four is the running-in period. Heat pumps are configured during commissioning to specific weather compensation curves, flow temperatures, and timer settings. The installer should return after 4-6 weeks to fine-tune based on actual operation. A surprising number don't, and the system runs sub-optimally as a result. Insist on the follow-up visit.
The myths that keep recurring
"Heat pumps don't work below freezing." Modern units work down to -15°C with reduced COP. UK winters in most areas don't go below -5°C. The pre-2018 generation of heat pumps had this problem; today's don't.
"They're loud." Modern outdoor units run 40-50 dB at 3 metres, quieter than typical UK air conditioning. Old units (pre-2018) were noisier. Permitted Development rules cap sound at 42 dB at the neighbouring boundary, which most installs comfortably meet.
"You have to replace every radiator." Sometimes; usually not. A heat-loss calc tells you which rooms have undersized radiators for the lower flow temperature. Often it's 2-4 radiators, not the whole house.
"The hot water isn't hot." UK heat pumps deliver hot water at 50-55°C and run a weekly legionella cycle to 60°C+. That's hot enough for showering and washing up. The myth is from people comparing it to a gas combi running at 60°C+ permanently.
"They use loads of electricity." They do, in absolute terms. They use 3-4x less primary energy than a gas boiler does to deliver the same heat, because of the COP. The electricity bill goes up; the gas bill goes to zero; the net total is lower if you're on the right tariff.
When you shouldn't fit one
The honest don't-do-it list:
- Listed building or restricted permitted development area where the outdoor unit is unlikely to get consent. Possible but expensive and uncertain.
- Single-glazed, uninsulated, leaky property where the radiators are 1970s-sized. Insulate first, or you'll be miserable in February.
- Plan to move within 3-5 years. Heat pump payback over gas isn't that fast; you'll lose money on the deal.
- Tight budget with no flexibility. Even with the £7,500 grant, the up-front capital is £1,500-£8,500. If that requires borrowing at high interest, the maths flips.
- Flat or apartment without somewhere to put the outdoor unit. Communal MVHR systems exist but they're a different conversation.
What goes alongside
The heat pump fits into a broader home-energy picture:
- Loft insulation is essentially a prerequisite, not an optional extra
- Cavity wall insulation where applicable, similar logic
- Smart thermostat matters more for heat pumps than gas boilers because of weather compensation
- Solar panels integrate well; daytime solar can run the heat pump for free in mild weather
- EV home charger shares the upgraded electrical capacity heat pumps often require
A whole-home retrofit (insulation + heat pump + solar + EV charger) typically lands at £25,000-£45,000 spread over a few years, with payback in the 15-20 year range. Worth it if you're staying long-term; questionable if you're not.
The biggest mistake I see people make is treating the heat pump as a drop-in boiler replacement. It isn't. It's a different system that wants different things from the building it's installed in. Get those things right and it's a genuinely good UK heating choice. Get them wrong and you'll spend the next decade regretting it.
This article is general consumer information about UK heat pumps, not building services advice. UK heat pump installation involves significant capital and expertise; use MCS-certified installers and verify Boiler Upgrade Scheme eligibility.
Affiliate disclosure: Morningfold has affiliate partnerships with several UK heat pump brands and installer marketplaces. See editorial standards.