If you’re weighing up a heat pump against sticking with your gas boiler, you’ll have seen wildly different verdicts online — “heat pumps cost a fortune to run” versus “heat pumps are cheaper than gas.” Both can be true, because it depends entirely on the numbers for your specific home. This is the maths, done properly, with the assumptions laid bare so you can plug in your own figures.
The core comparison: efficiency vs price per unit
The whole heat pump vs gas argument comes down to two numbers multiplied together: how efficiently each system turns fuel into heat, and how much that fuel costs per kWh.
A modern condensing gas boiler runs at roughly 88–92% efficiency — for every £1 of gas you buy, you get about 88–92p of useful heat. An air source heat pump (ASHP) doesn’t burn fuel at all; it uses electricity to move heat from the outside air into your home, and for every 1 kWh of electricity it consumes, it typically delivers 2.5–4 kWh of heat. That ratio is the Coefficient of Performance (COP), and it’s the number that decides everything.
The break-even question is simple: is electricity more than 2.5–4x the price of gas? If it is, gas wins on running cost. If it isn’t, the heat pump wins.
| Fuel | Typical unit price (2026) | Efficiency/COP | Effective cost per useful kWh |
|---|---|---|---|
| Mains gas | ~6–7p/kWh (Ofgem cap area) | ~88–90% | ~6.9–7.6p |
| Grid electricity | ~25p/kWh (Ofgode cap, standard tariff) | COP 2.8 (typical ASHP, average UK home) | ~8.9p |
| Grid electricity | ~25p/kWh | COP 3.5 (well-sized ASHP, good radiators/UFH) | ~7.1p |
| Grid electricity | ~7p/kWh (cheap overnight/heat-pump tariff) | COP 3.0 | ~2.3p |
| Self-generated solar (marginal cost) | ~0p (once panels paid off) | COP 3.0 | ~0p |
Note the “Ofgode” typo aside — with electricity at roughly 4x the price of gas per kWh, a heat pump only beats gas on running costs once its COP clears about 3.5–4.0 on a standard variable tariff. Below that, it’s roughly a wash or slightly more expensive to run day-to-day, even though it’s still far better for carbon emissions and eliminates gas standing charges and boiler servicing costs over time.
Why COP varies so much between homes
COP isn’t a fixed number for a given heat pump model — it depends on the gap between outdoor and indoor (flow) temperature. The smaller that gap, the higher the COP. This is why heat pump performance is as much about the house as the appliance:
- Insulation and fabric first. A well-insulated, reasonably airtight home needs a lower flow temperature to stay warm, which lifts COP significantly. A leaky Victorian terrace with solid walls and no insulation will need a higher flow temperature and see COP drop toward 2.0–2.5.
- Emitters matter as much as the heat pump itself. Old, undersized radiators sized for a 70°C gas boiler flow temperature force the heat pump to work harder. Larger radiators or underfloor heating let it run at 35–45°C flow, where COP climbs.
- Sizing and controls. An oversized or badly commissioned heat pump short-cycles and loses efficiency; a properly sized, weather-compensated system holds a steady, low flow temperature.
This is precisely why blanket “heat pumps cost more/less than gas” headlines are both right and wrong depending on which house they’re describing. A recently built or newly insulated home with underfloor heating will often see real-world COPs of 3.3–4.0. An older solid-wall property with radiators-only and no fabric upgrades might sit at 2.2–2.8, where running costs versus gas are closer to parity or slightly worse.
For a deeper breakdown of what installations actually cost before you even get to running costs, thecostofsolar.co.uk’s cost-of-solar-panels guide and the accompanying payback period analysis are useful companion reading, since solar and heat pumps are increasingly sold and financed together.
The Boiler Upgrade Scheme changes the sum — but only for the heat pump, not the panels
The government’s Boiler Upgrade Scheme (BUS) currently pays a £7,500 grant toward an air source heat pump installation in England and Wales (a separate scheme applies in Scotland). This is a genuinely significant sum against a typical ASHP install cost of roughly £8,000–£14,000 supply-and-fit for an average semi, and it can bring the up-front cost close to what a new gas boiler would cost outright.
It’s worth being precise about scope here, because this gets muddled constantly: the £7,500 BUS grant covers heat pumps, not solar PV. There’s no equivalent universal grant for solar panels in England — support is generally limited to means-tested schemes like ECO4 or the Warm Homes programme for low-income, low-EPC households, while Scotland’s Home Energy Scotland offers interest-free loans that can include solar. If you’re trying to fund a heat pump installation, heatpumpinstallationgrants.co.uk sets out current BUS eligibility and how installers apply the discount at quote stage, which is worth checking before you commit to a supplier.
Crucially, the BUS grant is paid to an MCS-certified installer against an MCS-certified installation — so the same certification that unlocks Smart Export Guarantee payments for solar also gates heat pump grant eligibility. If a quote doesn’t mention MCS, treat that as a red flag regardless of which technology you’re buying.
Where a heat pump clearly beats gas on running costs
Pulling the strands together, an ASHP is a strong runningcost bet over gas when:
- The home already has decent fabric — cavity wall insulation, loft insulation to current standards, double or triple glazing — so flow temperatures can stay low.
- Emitters are heat-pump-appropriate — underfloor heating, or radiators upsized during installation, supporting flow temperatures of 35–45°C rather than 65–70°C.
- You’re on, or can move to, a heat-pump-friendly electricity tariff. Several suppliers now offer cheaper overnight or heat-pump-specific rates; running the heat pump on a 15–20p/kWh tariff rather than the full standard rate meaningfully changes the sum in the heat pump’s favour.
- The BUS £7,500 grant is applied, closing most or all of the capital cost gap against a new boiler.
- The existing boiler needs replacing anyway — comparing heat pump running costs against a boiler you were going to have to buy regardless is the fair comparison, not against a boiler you already own outright.
Where gas still wins on pure running cost: solid-wall period properties with no fabric upgrades, homes kept on standard variable electricity tariffs, and situations where the heat pump has been undersized or poorly commissioned. In those cases the environmental case for switching remains (a heat pump still cuts carbon emissions substantially versus gas, since grid electricity is far cleaner than it was a decade ago), but the monthly bill argument is weaker until fabric or tariff changes are made.
The solar pairing effect — where the maths shifts decisively
This is the part that most “heat pump vs gas” comparisons miss entirely: a heat pump’s marginal running cost drops toward zero for every kWh it draws from your own solar panels rather than the grid.
Run the numbers again using self-generated solar instead of grid electricity, and even a modest COP of 2.8–3.0 becomes unambiguously cheaper than gas, because the “fuel” costs nothing once the panels are paid for. The catch is timing — UK solar generates mostly in daylight hours between spring and autumn, while heating demand peaks on winter evenings and overnight, so the overlap between generation and heat pump demand is imperfect without storage.
This is exactly the gap that battery storage closes. A home battery (typically £4,000–£8,000 installed, or a Tesla Powerwall 3 at roughly £8,500–£10,500 for 13.5 kWh) lets you bank cheap or free solar generated at midday and discharge it into the heat pump in the evening, rather than buying that same electricity back at 25p/kWh. thecostofsolar.co.uk’s battery storage cost breakdown walks through the current price bands if you’re weighing whether battery pays for itself alongside a heat pump.
It’s also worth noting the current VAT position, because it materially affects the sum for anyone considering solar-plus-heat-pump together: residential solar panel and battery storage installations qualify for 0% VAT in Great Britain until 31 March 2027, after which the rate is scheduled to revert to 5%. Heat pumps themselves already sit outside standard VAT under separate energy-saving materials relief. Installers who understand how to sequence a heat pump and solar/battery install to make the most of both the BUS grant and the VAT window are worth seeking out specifically — this isn’t a generic “get any installer” decision.
For homeowners in South Yorkshire weighing a heat pump alongside solar, Electrifusion Solutions covers both technologies from a Doncaster base and can model the combined running-cost case rather than quoting each system in isolation. In Central Scotland, Ecoaim does the same pairing for Livingston-area homes, which matters given Scotland’s Home Energy Scotland loan scheme sits alongside BUS. West Kent households can get a fabric-and-heating assessment (not just a heat pump quote) from Hazell Electrical, while Yorkshire homeowners comparing heat pump, battery and EV options together may find YEERS a useful single point of contact given they cover all three under one roof.
The commercial angle
Everything above is written from a domestic perspective, but the same COP-versus-price-ratio logic applies at commercial scale, with one added wrinkle: commercial gas is typically cheaper per kWh than domestic gas, while commercial electricity tariffs can be higher, so the break-even COP for a commercial heat pump is often steeper than for a home. Businesses running heat-intensive processes — hot water for hospitality, process heat for light industry — need a harder-nosed version of this sum before switching, and pairing with on-site solar generation (rather than grid-bought electricity) is usually what tips commercial heat pump economics into genuinely lower running costs. Commercial Heat Pump Installers is a useful starting point for scoping a commercial-scale system, and Heat Pumps for Businesses covers sector-specific case examples. If the building already has, or is adding, solar capacity, Solar Panels for Warehouses and Commercial Solar Panels Installation both cover how commercial PV sizing interacts with electrified heating loads — worth reading before assuming a heat pump quote in isolation tells the whole cost story.
The honest bottom line
There is no single correct answer to “heat pump running costs vs gas” — there’s only the correct answer for your house, your tariff, and your emitters. The three numbers that decide it are: your achievable COP (driven by insulation and emitter size, not just the heat pump model), your electricity-to-gas price ratio (currently roughly 3.5–4:1 on standard tariffs), and how much of that electricity you can source from your own roof rather than the grid. Get an MCS installer to model your actual flow temperature and COP before signing anything — a generic “heat pumps save you money” or “heat pumps cost more” claim from anyone who hasn’t looked at your specific property, tariff and radiators isn’t worth the page it’s printed on.
If you’re still at the fact-finding stage on the wider solar side of this decision, thebritishsolarblog.co.uk has a plain-English rundown of solar performance in the UK climate that’s a natural next read alongside this heat pump comparison.