The heat pump vs gas boiler debate is often framed in carbon terms. But for most homeowners making the decision in 2026, the question is simpler: which one costs less to run?
The Key Variable: Electricity-to-Gas Price Ratio
Heat pumps use electricity. Gas boilers use gas. The running cost comparison starts here.
| Fuel | Ofgem Price Cap Rate (Q2 2026) |
|---|---|
| Gas | 6.24p/kWh |
| Electricity | 24.5p/kWh |
Electricity is currently 3.9x more expensive per kWh than gas. For a heat pump to match gas running costs, it must therefore produce 3.9 units of heat for every 1 unit of electricity — a COP of 3.9.
In practice, well-installed UK heat pumps achieve SCOPs of 2.8–4.0. The gap between electricity and gas prices determines whether any given installation is cost-competitive.
Annual Running Cost Comparison
For a typical 3-bedroom semi-detached home requiring 12,000 kWh of heating per year:
| Heating system | Efficiency / COP | Annual fuel use | Unit rate | Annual cost |
|---|---|---|---|---|
| Gas boiler (older) | 80% | 15,000 kWh gas | 6.24p | £936 |
| Gas boiler (modern A-rated) | 92% | 13,043 kWh gas | 6.24p | £814 |
| ASHP (COP 2.5) | — | 4,800 kWh electricity | 24.5p | £1,176 |
| ASHP (COP 3.0) | — | 4,000 kWh electricity | 24.5p | £980 |
| ASHP (COP 3.5) | — | 3,429 kWh electricity | 24.5p | £840 |
| ASHP (COP 4.0) | — | 3,000 kWh electricity | 24.5p | £735 |
At current prices: A heat pump needs a COP of ~3.4 to match a modern gas boiler, and ~3.0 to match an older less-efficient boiler.
What COP Can You Realistically Expect?
COP varies by outdoor temperature, installation quality, and heat distribution system. UK field data from the Electrification of Heat trial shows:
| SCOP Range | Proportion of UK installations |
|---|---|
| Below 2.5 | ~15% (usually poor installations or unsuitable properties) |
| 2.5–3.0 | ~30% |
| 3.0–3.5 | ~35% |
| Above 3.5 | ~20% (good installations, well-insulated homes) |
The median UK heat pump SCOP is approximately 2.8–3.1. This means the average UK installation is marginally more expensive to run than a modern gas boiler at 2026 prices — but close enough that off-peak tariffs or rising gas prices tip the balance.
The Off-Peak Tariff Factor
Standard electricity at 24.5p/kWh makes heat pumps marginally uncompetitive with gas. But several tariffs offer significantly lower rates at off-peak times:
| Tariff | Off-peak rate | Peak rate | Suitable for heat pump? |
|---|---|---|---|
| Octopus Intelligent Go | ~7p/kWh (overnight) | 24.5p | Yes — excellent |
| Octopus Cosy | ~12p/kWh (selected hours) | 24.5p | Yes — good |
| OVO Heat Pump | ~12p/kWh (off-peak) | 24.5p | Yes |
| Economy 7 | ~10–15p/kWh (overnight) | 28–35p | Possibly — check rates |
A heat pump running on a 7p/kWh off-peak tariff (via Octopus Intelligent) at COP 2.8 produces heat at 2.5p/kWh — comfortably cheaper than gas. This fundamentally changes the economics.
With smart scheduling (heating water and spaces during cheap-rate periods, storing in a buffer tank or hot water cylinder), a heat pump home can achieve significantly lower bills than a gas home even at 2026 electricity prices.
When Does a Heat Pump Win?
A heat pump is cheaper to run than a gas boiler when any two or more of these conditions apply:
- SCOP of 3.5 or above (well-installed, good insulation, underfloor heating)
- Off-peak or time-of-use tariff with rates below 15p/kWh
- Replacing oil or LPG (where the comparison is much more favourable)
- Solar panels generating electricity during daytime heat pump operation
- Home heated primarily overnight or during cheap-rate hours
Upfront Cost Difference
When replacing heating systems, the upfront cost gap is significant:
| System | Installed cost | Available grant | Net cost |
|---|---|---|---|
| New A-rated gas boiler | £2,500–£4,500 | None | £2,500–£4,500 |
| Air source heat pump | £10,000–£18,000 | £7,500 (BUS) | £2,500–£10,500 |
| ASHP + hot water cylinder | £11,000–£20,000 | £7,500 (BUS) | £3,500–£12,500 |
The Boiler Upgrade Scheme (BUS) substantially narrows the gap. For a £12,000 heat pump with £7,500 BUS grant, the net cost over a new boiler may only be £3,000–£5,000 — recoverable in 10–20 years at even modest running cost savings.
The Carbon Case
Even if running costs are similar, heat pumps produce significantly fewer carbon emissions than gas boilers — particularly as the grid becomes greener. In 2026, the grid carbon intensity is approximately 150–200 gCO₂/kWh on average. An ASHP at COP 3.0 produces ~50–67g CO₂/kWh of heat, vs a gas boiler at ~200g CO₂/kWh. As the grid decarbonises, this advantage grows.
What Is SCOP and Why It Matters
SCOP (Seasonal Coefficient of Performance) is the average COP of a heat pump measured across an entire heating season, accounting for real-world conditions: cold snaps, mild days, domestic hot water production, and defrost cycles. It is a more realistic measure than the instantaneous COP quoted in product brochures.
A heat pump might have an instantaneous COP of 4.5 on a mild 7°C day but only 2.2 during a cold snap at -7°C. The SCOP averages this out. UK installers are now required to report SCOP under MCS standards.
Typical UK SCOP ranges:
- Air source heat pump (modern, well-installed): SCOP 2.8–3.5
- Ground source heat pump: SCOP 3.5–4.5
- Air source in poorly insulated home or at high flow temperature: SCOP 2.0–2.5
A SCOP of 3.0 means the heat pump produces 3 kWh of heat for every 1 kWh of electricity consumed. At current UK energy prices (electricity ~24.5p/kWh, gas ~6.2p/kWh), the running cost parity point is a SCOP of approximately 24.5 ÷ 6.2 = 3.95. This means most air source heat pumps still cost more per year to run than a high-efficiency gas boiler, unless the home is well-insulated.
Practical Steps to Optimise Heat Pump Running Costs
The difference between a heat pump running at SCOP 2.5 and SCOP 3.5 is significant — potentially £300–£500/year. To get the best performance:
- Lower the flow temperature — the lower the water temperature the heat pump needs to produce, the higher its efficiency. Aim for 35–45°C with underfloor heating, 45–55°C with radiators
- Run continuously at low output — heat pumps are most efficient running steadily at low output rather than cycling on and off. Do not turn the heat pump off overnight
- Upgrade radiators if needed — larger radiators achieve the same heat output at lower flow temperatures, boosting SCOP
- Insulate the hot water cylinder — heat lost from the cylinder is wasted energy; a well-insulated cylinder retains heat for longer
- Schedule domestic hot water during off-peak hours — if you have an Economy 7 or Octopus Go tariff, heating water at off-peak rates reduces cost significantly
- Annual service — a dirty heat exchanger or low refrigerant reduces efficiency; annual servicing maintains designed-for performance
Related Guides
- Are Heat Pumps Worth It Financially? — full ROI and payback analysis
- Air Source Heat Pumps UK — Costs and Grants — installation guide
- Is Solar Worth It UK? — pairing solar with a heat pump
- Green Technology hub — financial guide to all green home tech