Combi vs heat pump: the cost in one view
Strip out the marketing from both sides and the picture is simple. A combi wins clearly on upfront cost. The two are close on running cost at standard energy rates. The heat pump pulls ahead on running cost only with a dedicated heat-pump tariff, and carries a £7,500 grant the boiler does not. Whether it is "worth it" is really a question of how long you will stay, and which tariff you can get.
Gas combi boiler
£1,800 to £3,200
fitted, no grant
- ✓Cheap and quick to install.
- ✓Works in any home, no insulation upgrade needed.
- −No grant; tied to the gas price.
Air source heat pump
~£5,000
after the £7,500 grant (from £8,000 to £15,000)
- ✓£7,500 grant cuts the headline price.
- ✓Cheaper to run on a heat-pump tariff.
- −Needs a good install and a suitable home.
Why most comparisons mislead you
The heat-pump debate online tends to come from two equally unhelpful places: installers who need the sale, and gas-boiler defenders who want to dismiss the technology. Both flatten the one variable that actually decides the running-cost question: the electricity tariff.
A heat pump runs on electricity, which costs roughly four times as much per unit as gas at the price cap. It only beats gas because it is three times as efficient, it moves about three units of heat for every unit of electricity it draws (its SCOP). Do the maths at standard rates and the two technologies land within a small margin of each other. Switch to a heat-pump tariff priced near 15p per kWh, and the heat pump suddenly wins by hundreds a year. Any comparison that quotes "heat pumps save £X" without naming the tariff is leaving out the whole story.
Combi or heat pump: which costs less over time?
Every figure is yours to change. We add the upfront cost to the running cost year by year, and tell you when, if ever, the heat pump overtakes the boiler.
Running cost a year (fuel)
Total cost over years
Defaults verified June 2026: gas 5.74p/kWh and electricity 24.67p/kWh (Ofgem price cap), heat-pump tariff 15p/kWh (e.g. OVO Heat Pump Plus), boiler 88% efficient, combi £2,500 fitted, heat pump £5,000 net of the £7,500 grant. Fuel cost only; standing charges excluded as both options pay them.
How the running-cost maths actually works
To deliver the same warmth, a gas boiler at 88% efficiency burning the UK-average 11,500 kWh of gas costs roughly £660 a year in fuel at the 5.74p price-cap rate. A heat pump delivering the same heat at SCOP 3.0 needs about a third as much energy, but in electricity. At the 24.67p cap that works out close to the boiler, sometimes a little more, sometimes a little less depending on your exact efficiency.
Move that same heat pump onto a 15p heat-pump tariff and its yearly fuel cost drops to around £400 to £500, a clear saving of a few hundred pounds. That single switch, not the hardware, is what turns a heat pump from "about the same" into "genuinely cheaper". It is why the tariff toggle in the calculator above swings the verdict more than any other setting.
The insider view: you are buying a tariff, not a box
Here is the framing the industry rarely states plainly. With a gas boiler, your running cost is locked to a fuel you cannot shop around on much, gas is gas. With a heat pump, your running cost is locked to electricity, which you can shop around on hard. Heat-pump tariffs exist precisely because suppliers want that load, and they are likely to get cheaper as more flexible, off-peak electricity comes online.
The hidden risk that flips the decision A heat pump's whole economic case rests on the install quality. A poorly commissioned system running at SCOP 2.3 instead of 3.5 can cost more to run than the gas boiler it replaced, even on a cheap tariff. The grant and the tariff get the attention, but the survey and the installer are where the savings are actually won or lost. Choosing the cheapest install is the most expensive mistake in this whole decision.
So the real question is not "combi or heat pump" in the abstract. It is: can you get a high-quality install (high SCOP) and a heat-pump tariff? If yes, the total-cost gap to a boiler is small and shrinking, and the £7,500 grant tips it. If no, a combi remains the cheaper, simpler choice today, and there is no shame in that.
What to actually do
Run your own numbers
Use the calculator with your real heat demand and the tariff you can actually get. The default verdict is not your verdict.
Get an MCS heat-loss survey
A proper survey, not a rule-of-thumb, sets the SCOP you will really achieve. This is the figure your whole saving rests on.
Confirm a heat-pump tariff first
Check you can switch to a 15p heat-pump tariff before committing. Without it, the running-cost case is much weaker.
Claim the £7,500 grant
Your MCS installer applies for the Boiler Upgrade Scheme and takes it off the price. Make sure it is itemised on the quote.
The bottom line
A combi is cheaper to fit and works anywhere; a heat pump costs more upfront even after the £7,500 grant, but can cost less to run, if, and only if, you pair a good install with a heat-pump tariff. The upfront prices make the boiler look like the obvious winner. The total cost over the years you actually stay, on the tariff you can actually get, is a much closer race. Run your real numbers above before you let a headline price decide for you.
Combi vs heat pump FAQ
The Selectra expert answers your questions
It depends almost entirely on your electricity tariff. On a standard price-capped tariff, an air source heat pump (typical efficiency, SCOP around 3.0) is roughly level with a modern gas combi, the running cost can land slightly either side. On a dedicated heat-pump tariff such as OVO Heat Pump Plus (15p per kWh) or Octopus Cosy, the same heat pump can save £300 or more a year, because it uses electricity priced well below the cap. The hardware barely changes the answer; the tariff does.
Typically £8,000 to £15,000 before grants, with the Ofgem-reported average around £12,500 for an 8 kW system. The Boiler Upgrade Scheme takes £7,500 straight off for eligible homeowners in England and Wales, bringing the typical net cost to roughly £5,000. A new combi, by comparison, is about £1,800 to £3,200 fitted.
£7,500 towards an air source or ground source heat pump, for homeowners and small businesses in England and Wales replacing a fossil-fuel system. The installer must be MCS-certified and claims the grant on your behalf, so it comes off the price rather than being paid to you. The scheme is funded to 2030, and off-gas-grid properties can access £9,000 for a window from 21 July 2026. See GOV.UK.
Heat pumps work best in reasonably insulated homes with radiators sized for lower flow temperatures (or underfloor heating). A draughty, poorly insulated home will need insulation work first, or the heat pump will run hard and its efficiency (and savings) will fall. This is why the install quality and a proper heat-loss survey matter more than the brand. Get at least three MCS-certified quotes.
For a pure short-term cost decision, a combi is cheaper and simpler today. The case for a heat pump is the medium term: the £7,500 grant, falling heat-pump tariffs, and the long-term direction of gas pricing. If your boiler has years left, there is no rush. If it is failing and you can get on a heat-pump tariff, the total-cost gap is far smaller than the upfront prices suggest, run your own numbers in the calculator above.