Air Source Heat Pump Running Costs: What to Budget in the UK

The single biggest question stopping homeowners from switching to an air source heat pump is not the upfront cost — it's the running cost. Will the electricity bill be higher than the gas bill it replaces? The honest answer is: it depends, and the maths is not complicated once you understand it. This guide breaks down exactly how heat pump running costs are calculated, what a typical UK home pays today, how that compares to a gas boiler, and what you can do to make the numbers work in your favour.

How heat pump running costs are calculated

The formula is straightforward. An air source heat pump does not generate heat from electricity — it moves heat from outdoor air into your home. The ratio of heat output to electricity input is the Seasonal Coefficient of Performance (SCOP). A heat pump with a SCOP of 3.0 delivers 3 kWh of heat for every 1 kWh of electricity it consumes.

The running cost formula is:

Annual electricity cost = Annual heat demand (kWh) ÷ SCOP × electricity unit rate (p/kWh) ÷ 100

Three variables drive almost everything: how much heat your home needs, how efficiently your heat pump converts electricity to heat, and what you pay per unit of electricity. Each is worth understanding in detail before you look at the final cost.

Typical UK home heat demand

A three-bedroom semi-detached house in England typically uses 8,000 to 14,000 kWh of heat per year, depending on insulation quality, occupancy, and local climate. Ofgem's current typical domestic consumption value (TDCV) for a medium gas user is 11,500 kWh per year — this covers space heating and hot water combined. In practice, space heating alone accounts for roughly 60–70% of gas use, with the remainder going to hot water.

When switching to a heat pump, the headline heat demand figure stays the same (your home needs the same number of kWh of warmth), but the system now draws electricity rather than burning gas. A reasonably well-insulated three-bed semi requires roughly 10,000–12,000 kWh of useful heat annually. A poorly insulated pre-1980s property with single-glazed windows and no loft insulation may need 14,000 kWh or more. A well-insulated new-build or post-retrofit home could sit closer to 7,000–8,000 kWh.

Real-world SCOP vs the rated figure

The rated COP figure on a product sheet is a point-in-time measurement under laboratory conditions — typically at 7 °C outdoor and 35 °C flow temperature. Real UK installations deliver lower seasonal performance. The Energy Saving Trust's heat pump field trial, published on GOV.UK, measured an average SPFH4 (the whole-system seasonal efficiency including backup heating and pumps) of 2.45 for air source heat pumps in its Phase I dataset. A later, larger BEIS Electrification of Heat project recorded an average SPF of 2.81 across 742 homes.

Better-installed and better-maintained systems — those on platforms such as HeatpumpMonitor.org — average around 3.5–3.9. The practical range for most UK retrofits is SCOP 2.5–3.5, with the upper end achievable in well-insulated homes running at low flow temperatures. For planning purposes, assuming a SCOP of 2.8–3.2 is conservative and honest.

For a deeper explanation of how SCOP and COP figures are measured and what they mean for your specific system, see our heat pump efficiency and SCOP guide.

Why flow temperature matters so much

The single biggest driver of real-world SCOP is the flow temperature — the temperature of water the heat pump pushes through your radiators or underfloor heating. Every 5 °C increase in flow temperature reduces efficiency by roughly 10–15%.

• 35–40 °C flow temperature (underfloor heating or oversized radiators): SCOP 3.5–4.5. Achievable in well-insulated homes. Very competitive running costs.
• 45–50 °C flow temperature (modern radiators, reasonable insulation): SCOP 2.8–3.5. Typical retrofit with upgrades.
• 55–65 °C flow temperature (standard radiators, poorly insulated home): SCOP 2.0–2.8. Running costs substantially higher; may exceed gas costs at current prices.

If your home cannot be heated adequately at low flow temperatures, running costs rise sharply. This is why insulation and emitter upgrades are often recommended alongside heat pump installation.

Worked cost examples at April 2026 Ofgem price cap rates

From 1 April 2026, Ofgem's price cap sets the electricity unit rate at 24.67p/kWh and the gas unit rate at 5.74p/kWh (standard variable tariff, England/Scotland/Wales average, including 5% VAT). These are the reference figures used in the examples below.

The table uses a typical three-bedroom semi-detached house with an annual heat demand of 11,500 kWh (matching Ofgem's medium gas TDCV).

Heat pump scenarios

These figures cover only heat pump electricity consumption for space heating and hot water. Add roughly £50–80 per year for circulation pumps and controls.

Comparison against a gas boiler

A modern condensing gas boiler running on a standard variable tariff at 5.74p/kWh gas would cost approximately £660 per year to deliver 11,500 kWh of useful heat, assuming a boiler seasonal efficiency of 90% (a typical A-rated condensing boiler). Older boilers at 75–80% efficiency would cost £790–£840 per year for the same output.

Annual gas bills for typical UK three-bedroom homes currently run at around £900–£1,400 once standing charges are included — that bracket also captures variation in home size, insulation and thermostat habits.

Heat pump vs gas boiler: head-to-head at current rates

The Energy Saving Trust notes that at current energy prices, air source heat pumps are likely to cost slightly more to run than a new gas boiler in an average home, though they are generally cheaper to run than old or inefficient boilers. The EST also highlights that the gap narrows significantly — or reverses — when the heat pump benefits from a dedicated low-rate tariff.

If you are comparing options or looking at the best air source heat pumps for UK homes, pay close attention to the rated SCOP at 55 °C flow temperature (the A35/W55 figure), as this is what most standard-radiator retrofits will actually achieve in practice.

When heat pumps cost more — and when they cost less

Heat pumps cost more to run than a modern gas boiler when:

• The home is poorly insulated (EPC D or below with no insulation upgrades planned).
• The system is sized wrong or set to a high fixed flow temperature rather than using weather compensation.
• The household is on a standard electricity tariff and runs the heat pump during peak-rate hours.
• The SCOP falls below roughly 2.4 — at that point the electricity bill exceeds what gas would cost for the same heat output.

Heat pumps cost less than a gas boiler when:

• The home is well-insulated and the heat pump can run efficiently at low flow temperatures (SCOP ≥ 3.2).
• The household is on a heat pump–specific tariff such as Octopus Cosy, which offers rates up to 51% below the standard day rate during off-peak windows.
• The household also has solar panels: self-generated electricity at near-zero marginal cost dramatically improves the economics. Our guide on hybrid heat pump systems explores how combining a heat pump with your existing boiler and solar generation can optimise costs during the transition.
• Gas prices rise relative to electricity prices. The electricity-to-gas price ratio currently sits around 4:1; if the ratio fell to 2:1 (as government modelling suggests is achievable with a reformed grid), heat pumps would become much cheaper to run across almost all homes.

How insulation level affects running costs

Insulation is the most powerful lever you have over heat pump running costs. A poorly insulated home needs more heat (higher heat demand) and forces the heat pump to work at a higher flow temperature (lower SCOP) — a double penalty. Improving insulation can reduce annual running costs by £200–£500 in a single measure.

Practical steps that reduce heat demand and allow lower flow temperatures:

• Loft insulation — 270 mm mineral wool can cut roof heat loss by 75%. This is one of the cheapest and fastest payback measures. The Warm Homes Local Grant may fund this if your household income is below £36,000 and your EPC is D or below.
• Cavity wall insulation — a standard semi-detached can lose 35% of its heat through the walls. Cavity fill costs £400–£700 for most homes.
• Radiator upgrades — replacing standard-sized radiators with oversized versions (or adding a second radiator to each room) allows the heat pump to run at 45 °C instead of 55 °C, improving SCOP by 0.3–0.8 and saving £150–£250 annually at current rates.
• Thermostatic weather compensation — correctly configured weather compensation lowers flow temperature on mild days automatically, which is responsible for a large share of the performance gap between field-trial averages and well-optimised installs.

Dedicated heat pump tariffs and Economy 7

Moving to a heat pump–specific or time-of-use tariff is one of the most effective ways to cut running costs without touching the fabric of your home.

Octopus Cosy

Octopus Energy's Cosy tariff offers three “cosy windows” of super-cheap electricity every day: 04:00–07:00, 13:00–16:00, and 22:00–midnight. Rates in these windows are roughly 51% below the standard day rate. A heat pump household that shifts heating load into off-peak windows — particularly pre-heating the house overnight — can reduce annual electricity spend by £80–£200 compared with an equivalent standard-rate tariff. Eligibility requires a SMETS2 smart meter and an Octopus electricity account.

Economy 7

Economy 7 offers a 7-hour overnight cheap rate (typically around 11–15p/kWh) against a higher daytime rate (30–35p/kWh). For heat pumps, it works well only if you have good thermal mass (a warm home stays warm) or thermal storage (a large buffer tank that stores overnight-heated water). If the heat pump has to top up frequently during expensive daytime hours, Economy 7 can cost more than a flat rate. It is better suited to homes with strong insulation or buffer tanks.

Agile and half-hourly tariffs

Smart tariffs like Octopus Agile price electricity on a half-hourly basis tracking wholesale prices. When grid electricity is cheap (or even negative on windy days), heat pumps can run very cheaply indeed. Households with solar panels and a heat pump can combine these advantages: run the heat pump during the cheap overnight tariff windows, and during the day top up with self-generated solar electricity.

The Energy Saving Trust's running cost estimates

The Energy Saving Trust publishes guidance that a typical air source heat pump in a three-bedroom semi-detached home costs £900–£1,600 per year to run at current electricity prices, depending on insulation, system design, and tariff. The lower end of that range assumes a well-optimised system on a heat pump tariff; the upper end represents a suboptimal install on a standard variable tariff in a poorly insulated home.

For context, that £900–£1,600 range sits alongside annual gas bills of £900–£1,400 for equivalent homes. The overlap is real: the two systems are more evenly matched at current prices than marketing materials for either side tend to acknowledge.

What to expect in the long term

The electricity-to-gas price ratio is the key variable to watch. The UK government's Warm Homes Plan includes a commitment to reform electricity pricing to reduce the ratio — green levies currently make electricity artificially expensive relative to gas. If that ratio falls from the current ~4.3:1 toward 2:1, a heat pump with a SCOP of 2.5 would cost the same to run as a gas boiler at 90% efficiency, and a well-installed heat pump at SCOP 3.0–3.5 would be substantially cheaper.

The £7,500 Boiler Upgrade Scheme grant (or £2,500 for air-to-air units) reduces the capital cost barrier significantly and is available now. You can explore eligibility through an MCS-certified installer. For context on how the grant works alongside the broader government funding picture, our Warm Homes Plan guide explains the full range of available support routes for 2026.

For a broader view of whether the investment makes sense for your specific situation, see our guide on whether heat pumps are worth it in the UK — it covers the full cost-benefit picture including 20-year comparisons and who benefits most.

Practical planning checklist

1. Measure your current heat demand. Your annual gas consumption (from bills) minus roughly 30% (hot water + cooking) gives a ballpark for space heating demand.
2. Check your insulation status. Loft and cavity wall insulation should be addressed before or alongside heat pump installation. An EPC C or above makes the maths significantly better.
3. Understand your radiators. Ask your installer to do a heat loss calculation per room and confirm whether existing radiators can run at 45 °C or below. If not, radiator upgrades are cheaper than many people assume.
4. Set up weather compensation. Make sure your installer configures weather compensation correctly — this single setting is responsible for a large share of underperforming installs.
5. Switch to a heat pump tariff. As soon as your system is commissioned, compare Octopus Cosy and similar offerings. The savings are meaningful and require no hardware changes.
6. Get multiple quotes. Running costs vary partly due to design choices (buffer tank sizing, system configuration). A well-designed system will cost less to run every year.

If you are weighing whether a more efficient ground source system would further reduce your running costs, read our ground source heat pump guide — it includes a direct SCOP comparison and worked cost examples versus air source at today's price cap rates.