SCOP Explained — Heat Pump Efficiency Made Simple
SCOP is the single most important heat pump number you'll see — and the one that determines whether your install saves money vs gas. Explained simply, with what 'good' looks like for UK conditions.
What is SCOP, really?
SCOP = Seasonal Coefficient of Performance. It's the ratio of heat output to electricity input averaged across a typical heating season (Oct-March).
For example, if your heat pump produces 9,000 kWh of heat over winter while consuming 3,000 kWh of electricity, your SCOP is 9,000 ÷ 3,000 = 3.0.
How SCOP affects your bill
The key relationship: to beat gas on running cost, your SCOP must be higher than the electricity-to-gas price ratio.
At October 2025 Ofgem cap: gas is 6.99p/kWh, electricity is 26.35p/kWh. Ratio = 3.77×.
| SCOP | Performance | vs Gas (std cap) | vs Gas (Cosy) |
|---|---|---|---|
| 2.0 | Very poor | −40% (gas wins) | −5% (gas wins) |
| 2.4 | Poor (failed install) | −25% (gas wins) | +15% (HP wins) |
| 2.8 | Mediocre | −15% (gas wins) | +25% (HP wins) |
| 3.0 | Average UK | −10% (gas wins) | +25% (HP wins) |
| 3.4 | Good ASHP | −5% (gas wins) | +30% (HP wins) |
| 3.8 | Very good ASHP | +1% (HP wins) | +35% (HP wins) |
| 4.2 | Excellent (GSHP) | +10% (HP wins) | +40% (HP wins) |
Conclusion: on Octopus Cosy, even modest SCOPs beat gas. On standard cap, you need SCOP >3.7 to win — many UK installs don't hit this.
What's a "good" SCOP for UK conditions?
- Air source heat pump (ASHP):
- Excellent: 3.5+
- Good: 3.0-3.4
- OK: 2.7-3.0
- Poor: under 2.7
- Ground source heat pump (GSHP):
- Excellent: 4.2+
- Good: 3.8-4.1
- OK: 3.5-3.8
- Poor: under 3.5 (rare for GSHP)
- Hybrid (mixed heat pump + gas): typically 2.8-3.2 SCOP on the heat pump component
What drives SCOP up vs down?
Pushes SCOP UP:
- Low flow temperature — 40°C vs 55°C can add 0.5-1.0 to SCOP
- Correctly sized radiators — large enough to dissipate heat at low flow temp
- Underfloor heating — runs at 30-35°C ideal for heat pumps
- Weather compensation — modulates flow temp to outdoor conditions
- Well-insulated building fabric — less peak demand = more steady-state operation
- Modern R290 refrigerant — efficient at higher output temps
- Mild UK climate — South Coast SCOPs run ~0.3 higher than Highlands
Pushes SCOP DOWN:
- High flow temperature — needed if radiators are too small
- Undersized radiators — common in old gas-boiler retrofits
- Oversized heat pump — short cycles, never reaches efficient steady-state
- Manual on/off control — no weather compensation
- Cold climate — ASHP loses efficiency below 0°C
- Poor insulation — high peak demand forces full output
- Bad commissioning — refrigerant charge wrong, controls not tuned
How installer choice affects SCOP
This is the biggest variable buyers underestimate. Two identical Mitsubishi Ecodans in similar 3-bed homes:
- Installer A (sized correctly, large rads, 40°C flow, weather comp): SCOP 3.4
- Installer B (oversized pump, small rads, 55°C flow, manual control): SCOP 2.4
That's 0.6 SCOP difference = ~£350/year running cost = £5,000+ over 15 years. The pump is identical.
Lesson: prioritise installer quality over brand. Choose firms with:
- 100+ heat pump installs in 2024-25
- Strong Trustpilot reviews mentioning SCOP performance
- Use of weather compensation controllers
- Willingness to upsize radiators rather than push flow temperature up
SCOP vs COP — what's the difference?
COP (Coefficient of Performance) is the efficiency at a single point — e.g., 7°C outside, 35°C flow. Manufacturers show high COP numbers because they cherry-pick favourable conditions.
SCOP is the seasonal average across realistic UK conditions. Always compare SCOPs, not COPs.
SCOP after install — measuring real performance
Many heat pumps now have built-in SCOP monitoring via apps:
- Mitsubishi MELCloud — reports SCOP monthly
- Daikin Onecta — real-time COP + monthly SCOP
- Vaillant sensoApp — energy reports
If your actual SCOP is below the design spec, contact your installer for a recommissioning service. Common fixes: lower flow temperature, larger radiators, weather compensation activation.