If you’ve compared heat pump spec sheets, you’ve almost certainly run into two acronyms: COP and SCOP. They’re the single most important numbers for understanding how much a heat pump will actually cost to run — yet they’re also widely misunderstood. Here’s what each one really measures, how they differ, and why relying on the wrong one can lead to a bad buying decision.
What Is COP (Coefficient of Performance)?
COP measures how much heat energy a heat pump produces compared to how much electrical energy it consumes, at one specific moment, under one specific set of conditions (usually a fixed outdoor and indoor temperature).
Formula:
COP = Heat output (kW) ÷ Electrical energy input (kW)
Example: A heat pump with a COP of 4 delivers 4 kWh of heat for every 1 kWh of electricity it uses.
The key limitation of COP is that it’s a snapshot, not a real-world average. Manufacturers typically test and publish COP at a specific standardized condition (commonly 7°C outdoor / 35°C or 55°C water flow temperature). That number will look great on a mild autumn day and much lower during a January cold snap — but the spec sheet won’t tell you that just from the COP figure alone.
What Is SCOP (Seasonal Coefficient of Performance)?
SCOP solves that problem. It measures the heat pump’s efficiency averaged across an entire heating season, factoring in a full range of outdoor temperatures a system would realistically experience — from mild days to the coldest week of winter — based on a defined climate zone (Average, Warmer, or Colder, as used in EU testing standards).
Formula (simplified):
SCOP = Total heat delivered over the season ÷ Total electricity consumed over the season
Because SCOP accounts for colder temperatures, defrost cycles, and partial-load operation, it’s a far more realistic predictor of your actual energy bill than a single COP figure.
COP vs SCOP: Side-by-Side
| Factor | COP | SCOP |
|---|---|---|
| What it measures | Efficiency at one fixed condition | Average efficiency across a full heating season |
| Real-world accuracy | Low — best-case snapshot | High — reflects seasonal variation |
| Used for | Quick technical comparisons, lab testing | Real running costs, subsidy eligibility, energy labels |
| Typical values | 3.0–5.0 | 3.0–4.6 (varies by climate zone) |
| Found on | Technical datasheets | Energy Related Products (ErP) label, official ratings |
Why SCOP Matters More Than COP for Buyers
When you’re comparing two heat pump models, the one with the higher COP isn’t automatically the better choice. A unit optimized for a high COP at mild temperatures might lose efficiency sharply in cold weather, while another unit with a slightly lower COP might hold performance steady across the whole season — resulting in a higher SCOP and lower actual bills.
This is also why SCOP is the figure used on official EU energy labels (A+++ to D ratings) and in most government subsidy or grant eligibility calculations — regulators care about real seasonal performance, not a single best-case number.
How to Use These Numbers When Comparing Heat Pumps
- Never compare COP figures alone — check that they were tested under the same conditions (outdoor/indoor temperature), since manufacturers can choose favorable test points.
- Always check SCOP for your climate zone — a heat pump’s SCOP for «Colder» climates will be lower than its SCOP for «Average» or «Warmer» climates; make sure you’re looking at the value that matches where you live.
- Higher flow temperatures lower both figures — a system paired with underfloor heating (30–35°C flow) will show a much higher COP/SCOP than the same unit paired with high-temperature radiators (55–65°C flow).
- Look for the energy label rating, not just the raw number — it translates SCOP into a simple A+++ to D scale for quick comparison.
What Typical Values Mean in Practice
| SCOP | Approximate meaning |
|---|---|
| Below 2.5 | Poor efficiency — check sizing or installation quality |
| 3.0–3.5 | Solid, typical performance |
| 3.6–4.2 | High efficiency — well-suited to low-temperature emitters |
| 4.3+ | Excellent — usually paired with underfloor heating and a well-insulated home |
Frequently Asked Questions
Is a higher COP always better?
Not necessarily on its own — a high COP at one test condition doesn’t guarantee good performance across a full winter. SCOP is the better indicator of real-world value.
What SCOP should I look for when buying a heat pump?
Most well-designed modern systems fall between 3.5 and 4.5 SCOP; anything notably lower may indicate poor sizing, an older design, or a mismatch with your heat emitters.
Does SCOP already include the defrost cycle and backup heater use?
Yes — SCOP calculations under EU testing standards account for defrost cycles and any auxiliary electric heating used during extreme cold, giving a more complete seasonal picture.
Can COP and SCOP change after installation?
Yes — actual in-field performance depends on correct sizing, installation quality, water flow temperature, and how well the home retains heat, so real results can differ from lab-tested figures.