Heat Pump COP vs SCOP UK 2026: What the Numbers Mean

COP (Coefficient of Performance) is the ratio of heat output to electrical input at a specific set of conditions. A heat pump with COP 4.0 delivers 4 kWh of heat for every 1 kWh of electricity it draws.

The catch: COP is measured at a single operating point - usually A7/W35 (7°C outdoor air, 35°C flow temperature). That's a warm-ish outdoor temperature with a low-temperature heating system - basically the heat pump's most-efficient operating zone.

Other lab-test points you'll see:

• A2/W35 - 2°C outdoor (cold winter day), 35°C flow. COP drops vs A7/W35.
• A-7/W35 - minus 7°C outdoor (very cold), 35°C flow. COP can drop sharply, sometimes to 2.0-2.5.
• A7/W55 - 7°C outdoor, 55°C flow (radiator-temperature system). COP drops because higher flow temp = harder work.

A heat pump manufacturer can technically quote any of these as 'the COP' - some marketing materials cherry-pick the A7/W35 number because it's the highest. Always check which conditions a COP value was measured at.

SCOP (Seasonal Coefficient of Performance) is a weighted average of COP across an entire heating season. It blends performance at multiple outdoor temperatures - cold mornings, mild afternoons, frosty nights - to estimate real-world annual efficiency.

The UK SCOP rating is calculated for the 'Average' European climate zone (which approximates UK conditions reasonably well, though slightly milder than Scottish + northern English realities). SCOP weights:

• Cold-temperature hours (where COP is lowest)
• Mild-temperature hours (where COP is highest)
• Hot water reheats (where flow temp is higher + COP lower)
• Defrost cycles (where the unit consumes electricity to clear frost off the outdoor coil)

Result: SCOP is the more honest single number for predicting UK annual running cost. It also includes the energy losses you don't see in COP - standby power, control system draw, auxiliary heater top-ups for very cold weather.

To estimate annual running cost, you need a number that averages efficiency across the full UK climate. SCOP does that; COP doesn't. A worked example:

A heat pump with COP 4.5 at A7/W35 might have SCOP 3.6 across a UK heating season - because December-February operate at COP 2.5-3.0 (cold weather + frequent defrost cycles), not COP 4.5.

For a typical UK 3-bed semi (heat demand ~12,000 kWh/year):

• If you used COP 4.5 to estimate: 12,000 / 4.5 = 2,667 kWh electricity = ~GBP 720/year on a 27p tariff. Wrong - too low.
• Using SCOP 3.6: 12,000 / 3.6 = 3,333 kWh electricity = ~GBP 900/year on a 27p tariff. More realistic.
• On a heat-pump tariff (16p effective): 3,333 × 16p = ~GBP 530/year. Realistic.

The mistake is taking the marketing COP number + dividing into annual demand. That underestimates running cost by ~25-30%. Use SCOP for realistic estimates.

For UK installs in 2026, realistic SCOP values across product tiers:

• Mid-market mass-produced units (SCOP 3.5-4.0): Vaillant aroTHERM plus, Daikin Altherma 3 R, Mitsubishi Ecodan PUZ, Octopus Cosy 6. Most installs land in this band. Solid efficiency for typical UK conditions.
• Premium / new-tech units (SCOP 4.0-4.5): Vaillant aroTHERM SR, Mitsubishi Ecodan Hybrid (R290 refrigerant), Daikin Altherma 3 R EBLA series. Higher purchase cost but noticeably better cold-weather performance.
• R290-refrigerant units specifically (SCOP 4.0-4.7): the propane refrigerant R290 has thermodynamic advantages over older R32, particularly for low-temperature operation. Most premium 2026 units use R290.
• Older or oversized units (SCOP 2.5-3.2): a sign of either poor sizing or units installed before 2020-ish. If your existing heat pump shows performance in this range, it's worth investigating whether the sizing is correct.

Quick sanity check: divide manufacturer-claimed COP by ~1.25 to estimate likely realistic SCOP for UK conditions. A unit claiming COP 5.0 at A7/W35 typically delivers SCOP ~4.0 across a UK heating season; COP 4.0 typically delivers SCOP ~3.2.

1. Flow temperature. The biggest single factor. A heat pump running at 35°C flow has SCOP roughly 30-50% higher than one running at 55°C. This is why properly-sized underfloor heating or oversized radiators (running at lower flow temp) deliver dramatically better SCOP than tight-spec radiators forced to run at 55°C.

2. Heat pump sizing. An oversized heat pump cycles on/off frequently in mild weather, wasting energy on startup/shutdown losses. An undersized unit runs flat-out + supplements with auxiliary electric heating in cold weather, both reducing SCOP. Correct sizing via MCS heat-loss calculation is essential.

3. Hot water demand pattern. Frequent small hot-water reheats (e.g. 5-person household with staggered showers) hit SCOP harder than infrequent larger reheats. A well-insulated hot water cylinder + scheduled reheat windows improve overall SCOP.

4. Defrost cycle frequency. Heat pumps regularly run brief reverse-cycle defrost passes to clear frost off the outdoor coil. The frequency depends on outdoor humidity + temperature. Some sites are worse than others (coastal locations + boggy rural sites = more frequent defrost = lower SCOP).

5. Refrigerant choice + unit age. R290 (propane) units outperform R32 units in cold weather; both significantly outperform older R410A units. A 2018 R410A heat pump might show SCOP 2.8 where a 2026 R290 unit on the same site delivers SCOP 4.2.

When comparing heat pumps from different manufacturers, normalise on these conditions:

• Use SCOP, not COP. SCOP is regulated under ErP rules + manufacturers must report it on the energy label. COP is more variable in how it's reported.
• Match flow temperature. Compare SCOP at 35°C across all units (or 55°C if all your existing radiators force that flow temp). Don't compare unit A's SCOP at 35°C with unit B's SCOP at 55°C - they're different operating points.
• Match climate zone. Use SCOP rated for 'Average' European climate (the UK proxy). Some manufacturers report SCOP for 'Warmer' climate which gives an artificially higher number.
• Confirm with installer for your specific install. Lab SCOP is a baseline; your install's real SCOP depends on flow temperature + sizing + radiator/UFH layout. A reputable installer should be able to model expected SCOP for your specific property.