The short answer
Whether a heat pump is cheaper to run than gas depends on two things: the pump's efficiency (SCOP) and the price ratio between electricity and gas. A gas boiler is around 90% efficient, so a unit of gas gives roughly 0.9 units of heat. A heat pump with a SCOP of 3 to 4 delivers 3 to 4 units of heat per unit of electricity. The catch is that under the UK price cap, electricity costs roughly 3 to 4 times as much per kWh as gas. That means a well-performing heat pump (SCOP around 3.5 or above) on a standard tariff lands roughly level with or below gas running costs, while a poorly set-up heat pump (low SCOP) on a standard tariff can cost more. Heat-pump-specific tariffs with cheaper off-peak electricity tilt the comparison clearly in the heat pump's favour.
The running-cost comparison is genuinely close in the UK, and small details swing it. The maths comes down to efficiency versus the price-per-unit gap between the two fuels.
Heat pump vs gas running cost
- Gas boiler efficiency~90%
- Heat pump efficiency (SCOP)~3–4
- Electricity-to-gas price ratio (price cap)~3–4×
- Decides the outcomeSCOP vs the price ratio
- Biggest saving leverHeat-pump tariff + high SCOP
The maths behind the comparison
The comparison hinges on a simple idea: a heat pump uses electricity far more efficiently for heating than a boiler uses gas, but each unit of electricity costs more. To find which wins, you compare the cost per unit of useful heat.
- Gas boiler: at about 90% efficiency, the cost of useful heat is roughly the gas unit price divided by 0.9.
- Heat pump: the cost of useful heat is the electricity unit price divided by the SCOP (3 to 4).
If electricity costs about 3.5 times as much as gas, a heat pump needs a SCOP of around 3.5 just to break even with gas on a standard tariff. Above that, it is cheaper; below it, more expensive. This is why getting the SCOP high — through good design, correct sizing and low flow temperatures — is the single most important factor for running cost.
| Scenario | Effective heat cost basis | Outcome vs gas |
|---|---|---|
| Gas boiler (~90%) | Gas unit price ÷ 0.9 | Baseline |
| Heat pump, SCOP 2.5, standard tariff | Elec price ÷ 2.5 | Often more expensive than gas |
| Heat pump, SCOP 3.5, standard tariff | Elec price ÷ 3.5 | Roughly level with gas |
| Heat pump, SCOP 4, standard tariff | Elec price ÷ 4 | Usually cheaper than gas |
| Heat pump on a heat-pump tariff | Lower off-peak elec ÷ SCOP | Clearly cheaper than gas |
Illustrative comparison based on the electricity-to-gas price ratio under the UK price cap. Sources: Energy Saving Trust; Nesta. Actual outcome depends on tariff and measured SCOP.
Why SCOP is the deciding factor
SCOP (Seasonal Coefficient of Performance) is the heat pump's average efficiency across a heating season. A well-designed system running at low flow temperatures into correctly sized radiators or underfloor heating achieves a higher SCOP; a system forced to run hot to compensate for small radiators achieves a lower one.
- Correct sizing: an oversized or undersized heat pump runs less efficiently.
- Low flow temperatures: the lower the temperature the system runs at, the higher the SCOP. This is why radiator upgrades and good system design matter to running cost, not just comfort.
- Good controls: weather compensation and steady, continuous running tend to beat short, hot bursts.
Other factors that affect the comparison
Beyond SCOP and tariff, a few other things influence whether a heat pump beats gas on running cost:
- Standing charges: if you remove a gas boiler entirely and disconnect from the gas grid, you no longer pay the gas standing charge, which adds a small ongoing saving. If you keep gas for cooking, you still pay it.
- Hot water: a heat pump heats water to a slightly lower temperature and stores it in a cylinder, with a periodic higher-temperature cycle for hygiene. How hot water is used and stored affects overall efficiency.
- Insulation and heat demand: a well-insulated home with a lower heat demand costs less to run on any system, and lets the heat pump run at a lower, more efficient flow temperature — improving its position against gas.
- Weather: in a mild winter a heat pump spends more time at high efficiency; in a very cold snap its efficiency dips and it uses more electricity, narrowing the advantage on those days.
- How you use the heating: heat pumps reward steady, continuous running at a low temperature rather than short hot bursts, so a heating pattern suited to the technology helps keep costs down.
These factors explain why two households with identical equipment can report different experiences. The running-cost outcome is the product of the system, the home and the way it is used and tariffed.
Where tariffs change everything
The standard price cap ratio is not the only option. Several UK suppliers offer heat-pump-specific or time-of-use tariffs with much cheaper electricity at certain times:
- Heat pump tariffs (for example, those aimed specifically at heat pump owners) offer reduced unit rates that narrow or close the gap with gas.
- Time-of-use tariffs with cheap overnight rates let a well-controlled heat pump heat water and pre-heat the home when electricity prices are lowest.
On these tariffs, a competent heat pump installation is usually clearly cheaper to run than a gas boiler. The combination of a high SCOP and a favourable electricity tariff is what tips the comparison decisively.
Frequently asked questions
Why is electricity more expensive than gas per unit in the UK?
Per kWh, electricity has historically cost several times more than gas under the UK price cap. This reflects how each is produced, supplied and levied. Because a heat pump runs on electricity, this price gap is the main reason the running-cost comparison with gas is close — the heat pump's efficiency has to overcome the higher price per unit.
What SCOP do I need for a heat pump to beat gas?
As a rough guide, if electricity costs about 3.5 times as much as gas, a heat pump needs a SCOP of around 3.5 to break even with a 90%-efficient gas boiler on a standard tariff. Above that it is cheaper; below it, more expensive. A heat-pump-specific tariff lowers the SCOP needed to come out ahead.
Can a heat pump end up more expensive to run than gas?
Yes — a poorly designed or badly sized heat pump running at high flow temperatures can have a low SCOP, and on a standard tariff that can cost more than gas. The way to avoid this is correct sizing, low flow temperatures (with radiator upgrades where needed) and, ideally, a heat-pump tariff.
Sources & further reading
- Energy Saving Trust — air source heat pumps (running costs)
- Nesta — the future of home heating
- Ofgem — energy price cap
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.