Heat Pump SCOP and COP Explained: What the Numbers Actually Mean
When you’re comparing heat pumps, you’ll come across two efficiency metrics: COP (Coefficient of Performance) and SCOP (Seasonal Coefficient of Performance). Both measure how much heat a pump produces per unit of electricity consumed, but they measure it in very different ways. COP is a snapshot taken in a lab at a specific temperature. SCOP is the number that reflects what you’ll actually pay to heat your home across a UK winter. Understanding the difference is essential if you want to make a meaningful comparison between models.
What Is COP (Coefficient of Performance)?
COP is the ratio of heat output to electrical energy input at a single, fixed operating point. If a heat pump uses 1 kW of electricity to produce 3 kW of heat, its COP is 3. Simple enough — but the problem is that COP is always measured at a standardised test condition, most commonly A7/W35: outdoor air temperature of +7°C, flow temperature of 35°C.
In practice, your heat pump operates across a wide range of outdoor temperatures — from above 10°C on mild autumn days to well below 0°C during a cold snap. As outdoor temperature falls, heat pump efficiency drops. A unit with a COP of 4.0 at +7°C might have a COP of just 2.2 at -7°C. The lab number tells you the ceiling, not the average.
COP is useful for engineering comparisons between test conditions, but it’s not the right metric for predicting energy bills. That’s where SCOP comes in.
What Is SCOP (Seasonal Coefficient of Performance)?
SCOP — Seasonal Coefficient of Performance — averages the heat pump’s efficiency across an entire heating season, factoring in the full range of temperatures that occur in a given climate zone. It accounts for cold snaps when efficiency falls, mild days when the heat pump barely needs to work, and everything in between.
SCOP ratings are standardised under the EU EN 14825 standard (retained in UK law post-Brexit) and calculated for three climate zones:
- Average climate (Strasbourg reference) — the rating most commonly quoted on product datasheets
- Warmer climate (Athens reference) — more favourable; higher SCOP values
- Colder climate (Helsinki reference) — more demanding; lower SCOP values
The UK’s climate sits roughly between the Average and Colder reference points. This means that the “average climate” SCOP on a datasheet is slightly optimistic for most of the UK, though not wildly so. For Scotland and exposed northern areas, lean towards the colder climate figure if the manufacturer provides it.
Why SCOP Matters More Than COP for UK Buyers
Your energy bill is based on how much electricity your heat pump uses across the entire heating season — not at one test point. SCOP gives you a much better basis for estimating annual running costs.
Here’s a worked example. Suppose your home requires 12,000 kWh of heat per year:
| Metric | Heat pump A | Heat pump B |
|---|---|---|
| COP at A7/W35 | 4.2 | 3.8 |
| SCOP (average climate) | 3.2 | 3.5 |
| Electricity used (12,000 kWh heat) | 3,750 kWh | 3,429 kWh |
| Annual cost at 28p/kWh | £1,050 | £960 |
| Difference | — | £90/year cheaper |
Heat pump A has the higher COP — the number most prominently advertised — but heat pump B has the higher SCOP and is cheaper to run across the year. This happens because some units perform extremely well at the narrow test condition but lose efficiency more steeply as temperatures drop. SCOP captures that drop-off; COP doesn’t.
For a deeper look at how efficiency affects annual bills, see our guide to heat pump running costs in the UK.
Typical SCOP Values for UK Heat Pumps
UK heat pumps typically achieve SCOP values in the following ranges, based on current product ranges from major manufacturers:
| System type | Typical SCOP range | Notes |
|---|---|---|
| Air source (budget models) | 2.5–3.0 | Older or smaller units, less advanced compressors |
| Air source (mid-range) | 3.0–3.5 | Most current residential products |
| Air source (high efficiency) | 3.5–4.2 | Inverter-driven, variable-speed compressors |
| Ground source | 3.5–5.0 | Ground loop provides more stable source temperature |
Ground source heat pumps tend to have higher SCOP values because the ground temperature (typically 10–12°C in the UK) remains stable year-round, avoiding the efficiency losses that air source units suffer in cold snaps. This is one of the key practical trade-offs explored in our heat pump efficiency guide.
ErP Ratings: The Letter Grade System
The Energy-related Products (ErP) Directive requires heat pumps sold in the UK to carry an energy efficiency label — the familiar A+++ to G scale. For heat pumps, these ratings are directly derived from SCOP:
- A+++ (SCOP ≥ 5.1) — exceptional; typically high-end ground source only
- A++ (SCOP 4.6–5.0) — best air source units and most ground source
- A+ (SCOP 3.8–4.5) — good air source performance
- A (SCOP 3.3–3.7) — adequate; typical mid-range air source
- B and below — avoid if buying new
ErP labels use the “average climate” SCOP as their basis, so the label gives you a quick comparative tool — though as noted, the UK’s real-world performance sits slightly below the label figure in colder regions. The Heat Pump Association provides guidance on reading product specifications for UK conditions.
Flow Temperature and Its Effect on SCOP
One factor that dramatically affects real-world SCOP is the flow temperature your system is designed to run at. Heat pumps become less efficient as the gap between the outdoor temperature and the target flow temperature widens.
This is why underfloor heating — which typically operates at 35–40°C flow temperature — pairs so well with heat pumps, while older radiator systems designed for 70–80°C flow can be problematic. A system running at 35°C flow might achieve SCOP 3.5; the same unit running at 55°C flow might achieve only SCOP 2.5. That’s a 40% difference in running costs for the same outdoor conditions.
If you’re retrofitting a heat pump into a home with existing radiators, getting a heat loss calculation done and potentially upsizing radiators is not optional — it’s how you actually achieve the SCOP values on the datasheet. Read more on this in our guide to heat pump installation in the UK.
How to Compare Models Using SCOP
When shortlisting heat pumps, follow these steps to make a meaningful comparison:
- Compare SCOP at the same flow temperature. Most manufacturers publish SCOP at W35 (35°C flow) and W55 (55°C flow). Use the figure that matches your planned system design.
- Use the same climate reference. “Average climate” SCOP values are comparable across brands. Don’t compare an average climate figure from one brand with a warmer climate figure from another.
- Check if SCOP includes backup heater operation. Some all-in-one units include an electric immersion element that runs in very cold weather. If this is factored into the SCOP figure, the system-level rating may look better than the heat pump alone warrants.
- Look at the full temperature curve. Better manufacturers publish COP values at multiple outdoor temperatures (e.g., A-15, A-7, A2, A7, A12). A unit that maintains 2.5 COP at -10°C is more useful in a UK cold snap than one that collapses to 1.8.
The Ofgem certification database and the Energy Saving Trust both provide resources for evaluating heat pump products for the UK market.
Real-World SCOP vs Rated SCOP: The Gap
It’s worth being honest: real-world SCOP often falls short of the rated figure. Reasons include:
- Systems oversized for the heat load spend more time cycling on and off (less efficient than steady operation)
- Hot water production requires higher flow temperatures, dragging down seasonal averages
- Backup electric elements running during extreme cold periods aren’t always reflected in ratings
- Poor system design — insufficient radiator size, uninsulated pipework, incorrectly set weather compensation
A well-designed, properly installed system from a competent MCS-certified installer should get reasonably close to rated SCOP. A poorly designed one might achieve 20–30% below it. This is why installation quality matters as much as the product specification — as we cover in our heat pump suitability guide.
The Bottom Line on SCOP and COP
COP is a useful number for engineers and for understanding a heat pump’s peak capability. For UK homeowners trying to choose between models or estimate annual running costs, SCOP is the figure that matters. Always compare like-for-like (same flow temperature, same climate reference), and remember that installation quality determines whether you actually achieve the rated seasonal efficiency in practice.
A heat pump with a SCOP of 3.5 will save you roughly 20% on electricity compared to one with a SCOP of 2.9 — on a £1,000/year heating bill, that’s £200 annually, compounding over a 15-year system lifespan. The numbers are worth understanding before you buy.