Heat Pump COP: What It Means for Your Electricity Bill
Every 0.5 improvement in your heat pump's COP saves you £50-80 per year on electricity. COP (Coefficient of Performance) is the single most important number for understanding your heat pump's running costs — yet most homeowners never check theirs. A COP of 3.0 means your heat pump produces 3 kWh of heat for every 1 kWh of electricity. Push it to 4.0 and you get a third more heat from the same electricity.
This guide explains COP in practical terms: what it means for your bill, how to check yours, and the concrete steps to improve it.
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What Is COP?
COP stands for Coefficient of Performance. It measures how efficiently your heat pump converts electricity into heat:
COP 2.5
2.5 kWh heat per 1 kWh electricity
Below average
COP 3.2
3.2 kWh heat per 1 kWh electricity
Typical UK ASHP
COP 4.0
4.0 kWh heat per 1 kWh electricity
Well-optimised system
By comparison, a gas boiler has an efficiency of about 0.9 (90%) — it produces 0.9 kWh of heat per 1 kWh of gas. Even at a modest COP of 3.0, a heat pump is over three times more efficient than a boiler in energy terms.
How COP Affects Your Bill
For a home needing 12,000 kWh of heat per year (typical 3-bed semi):
The difference between COP 2.5 and COP 4.0 is £270 per year — every year, for the life of the system. That is why optimising COP is so important.
How to Improve Your COP
- Lower flow temperatures: Drop from 50 degrees to 35 degrees and COP improves by 30-40%. This requires adequately sized radiators
- Improve insulation: Better insulation reduces heat demand, allowing lower flow temperatures
- Enable weather compensation: Automatically adjusts flow temperature based on outdoor conditions
- Ensure proper system balancing: All radiators should be balanced for even heat distribution
- Regular servicing: Keep the system clean and refrigerant charge correct
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Seasonal COP Variation
| Outdoor Temperature | Typical COP (35°C flow) | Typical COP (45°C flow) |
|---|---|---|
| 15°C (mild autumn) | 4.5-5.0 | 3.5-4.0 |
| 7°C (typical UK winter) | 3.5-4.0 | 2.8-3.2 |
| 0°C (cold winter) | 2.8-3.2 | 2.2-2.7 |
| -5°C (severe cold) | 2.3-2.8 | 1.8-2.3 |
Lower flow temperatures consistently deliver better COP at every outdoor temperature. This is why insulation is so important.
The seasonal COP (SCOP) averages performance across the entire heating season. A well-installed UK air source heat pump typically achieves SCOP 3.0-3.5. Ground source heat pumps achieve SCOP 3.5-4.5 because ground temperature is more stable than air.
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Frequently Asked Questions
What is a good COP for a heat pump?
A seasonal COP of 3.0-3.5 is typical for a well-installed UK air source heat pump. Ground source typically achieves 3.5-4.5.
How does COP affect my electricity bill?
Higher COP means lower bills. At COP 3.0, you need 1,000 kWh of electricity for 3,000 kWh of heat. At COP 4.0, you only need 750 kWh — a 25% saving. On Octopus Cosy, that is roughly £37-60 per year difference per COP point.
Does COP change with the weather?
Yes. COP drops as outdoor temperature falls. The seasonal COP averages this across the entire heating season.
How can I improve my heat pump's COP?
Lower flow temperatures (biggest impact), improve insulation, ensure radiators are correctly sized, and use weather compensation. Each 5 degree reduction in flow temperature improves COP by roughly 10-15%.
Is COP the same as efficiency?
COP is a measure of efficiency. COP 3.0 means 300% efficiency — the heat pump produces 3 units of heat from 1 unit of electricity. A gas boiler is around 90% efficient.
COP and the Economics of UK Heat Pumps
COP is the technical metric that underpins the financial case for heat pumps. With electricity costing 2.5-4 times more than gas per kWh, a heat pump needs a COP of at least 2.5 to match gas boiler running costs. Most well-installed systems comfortably exceed this, especially when combined with the right electricity tariff, good insulation, and potentially solar panels. The Boiler Upgrade Scheme grant of £7,500 addresses the upfront cost gap, while high COP addresses the running cost question.