CONSIDERED HOME ENERGY TOOLKIT
Heat Pump Running Cost Calculator
Heat pump vs gas boiler is one of the most searched, most anxiety-inducing home energy decisions in the UK right now — and most of the numbers floating around are either manufacturer best-case SCOP figures or a single scary anecdote. This uses a real-world SCOP range instead of a marketing one, your actual gas usage, and current Ofgem price cap rates, to give an honest answer for your specific home.
✓ Uses real-world SCOP ranges (2.2–3.6) tied to your insulation and radiator setup, not a manufacturer's lab figure
✓ Includes the Boiler Upgrade Scheme grant, and an honest "would you replace the boiler anyway?" adjustment
✓ Doesn't assume the answer — a poorly-suited setup can genuinely cost more to run, and this will say so
A running-cost and payback estimate, not a heat loss survey. A proper installer quote will come with a room-by-room heat loss calculation and a specified flow temperature — use this to get an honest first read before you get that. Thinking about pairing a heat pump with solar and a battery? Try the Home Energy Investment Calculator. Adding a heat pump alongside existing generation? Check the G98/G99 Export Limitation Checker for what it means for your supply.
1. YOUR CURRENT HEATING
Gas usage and boiler
Used to work out how much useful heat your home actually needs each year — the fairest baseline to compare a heat pump against.
2. YOUR PROSPECTIVE HEAT PUMP
Realistic efficiency for your home
This is the number that actually decides whether a heat pump saves you money — and it's the one most often oversold.
3. INSTALLED COST & GRANT
What it actually costs to switch
Your estimate
Running cost verdict
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Gas boiler / year
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Heat pump / year
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Running cost saving—
Net cost after grant—
Simple payback—
Grant applied—
ℹNot counted above: switching fully off gas also removes your gas standing charge (currently around 29p/day, roughly £106/year) — a genuine extra saving on top of the running-cost figures here, left out because it depends on whether you keep a gas connection for cooking or anything else.
Common mistakes
- Using a manufacturer's headline SCOP instead of a realistic figure for your actual insulation and radiators.
- Not lowering flow temperature after installation — a heat pump left running at boiler-style flow temperatures will underperform badly.
- Comparing the full heat pump cost against $0, when a gas boiler needing replacement soon isn't free either.
- Forgetting a heat-pump-specific tariff exists — running one on a standard variable rate leaves real savings on the table.
- Assuming the Boiler Upgrade Scheme grant arrives as cash to you — it's deducted upfront from the installer's quote instead.
- Sizing a heat pump like a boiler (oversized, cycling on/off) rather than for steady, longer, lower-temperature running.
Also considering solar and a battery?Model the combined payback with your real tariff
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Already have solar or a battery?See what adding a heat pump means for your DNO supply
→
See the assumptions used
Illustrative only, not a heat loss survey or financial advice. Real running costs depend on your actual heat loss, flow temperature, hot water habits and weather. Regulatory and grant details reflect our understanding as of 10 August 2026 and may have changed since — always confirm current grant terms on gov.uk and get a proper MCS-certified heat loss survey before buying.
THE NUMBER THAT ACTUALLY MATTERS
What pushes real-world SCOP up or down
Two identical heat pumps in two different houses can land 30–40% apart in efficiency — almost entirely down to these.
✓ Helps your SCOP
- Low flow temperature (35–45°C) — the single biggest lever. Roughly 10–15% better efficiency for every 10°C the flow temperature drops.
- Good insulation — lets the heat pump run gently and continuously rather than working hard to catch up.
- Underfloor heating, or radiators sized up for a heat pump — more surface area means the same heat output at a lower flow temperature.
- Correct sizing and commissioning — based on an actual room-by-room heat loss calculation, not a rule of thumb.
✕ Hurts your SCOP
- High flow temperatures (55°C+) — common when a heat pump is fitted onto an unmodified boiler-era radiator system.
- Poor insulation — the heat pump has to work harder and longer to hold temperature, especially in cold snaps.
- Undersized radiators left unchanged from a gas boiler install — forces a higher flow temperature to compensate.
- Marketing SCOP figures themselves — lab-tested best-case numbers, not a promise about your specific house.
UK winters are generally mild enough that a well-specified heat pump routinely achieves a real-world SCOP of 2.8–3.5 in an average home — the 2.2–2.6 and 3.6+ bands in Step 2 represent the poorly-optimised and well-optimised ends of that spread, not typical or exceptional cases.
THE BOILER UPGRADE SCHEME
The grant, in plain terms
A government grant toward the upfront cost of an air source or ground source heat pump in England and Wales, applied by your installer rather than claimed by you.
£7,500 standard grantFor air source and ground source heat pump installs replacing a fossil fuel or non-heat-pump electric heating system.
£9,000 off-gas-grid, time-limitedFrom 21 July 2026 to 31 March 2027, eligible properties not connected to mains gas (oil, LPG, electric heating) can get an enhanced £9,000 grant instead.
Deducted upfront, not paid to youYour installer takes the grant amount off their quote before you pay — there's no separate claim or reimbursement step for you to do.
MCS-certified installer requiredThe installer must be certified by the Microgeneration Certification Scheme and a member of an approved consumer code for you to qualify.
Scotland and Northern Ireland run separate schemes with different amounts and rules — this grant is specifically for England and Wales. Check current terms and full eligibility on gov.uk's Boiler Upgrade Scheme page before relying on a figure here.
How this tool works
Your annual gas usage is treated as the input energy to your current boiler. Multiplying it by boiler efficiency gives an estimate of the useful heat your home actually needs each year (space heating and hot water combined) — the fairest baseline, since it's based on what your home has actually needed, not a generic average. That useful heat figure is then divided by the heat pump's real-world SCOP to estimate the heat pump's own annual electricity use. Each side is then multiplied by its own price per kWh to get an annual running cost, and the difference is the running-cost saving.
SCOP conventionally describes space-heating performance; hot water is usually a little less efficient to produce with a heat pump. This tool doesn't split the two out separately — the "real-world SCOP" bands in Step 2 are deliberately chosen from real-world whole-system figures (which already reflect a hot water penalty in practice) rather than a lab space-heating-only number, so the simplification errs toward realistic rather than optimistic.
The heat-pump-tariff option in Step 2 applies an illustrative ~15% discount to the standard price-cap rate, representing a rough blend of off-peak, standard and peak periods on a typical time-of-use heat-pump tariff (for example Cosy Octopus, which offers roughly 8 off-peak hours around 50% cheaper than standard, and a 3-hour evening peak roughly 30% more expensive). Actual rates vary by region, change with wholesale prices, and depend on how much of your heating you can shift into off-peak hours — treat this as a starting estimate and check your supplier's current published rates, not a quote.
Simple payback divides the net installed cost (heat pump cost, minus the Boiler Upgrade Scheme grant, minus an avoided-replacement-boiler cost if you said you'd be replacing your boiler soon anyway) by the annual running-cost saving. If running costs come out higher for the heat pump than the current boiler, no payback period is shown — that's a genuine possible outcome with a low real-world SCOP and/or a standard electricity tariff, not a bug, and the verdict says so plainly rather than hiding it.
Not modelled: weather variation year to year, any solar/battery interaction (see the Home Energy Investment Calculator for that), and the removed gas standing charge if you leave the gas network entirely (flagged separately above, not included in the headline saving since many homes keep a gas connection for cooking).