Basics · 5 min read · Updated 2026-05-07
COP vs SCOP — which number should you trust?
COP is a single test point, SCOP is a season-weighted average. Use both, but for purchase decisions SCOP is what matches your wallet.
Two numbers, two purposes
A glossy spec sheet might list the same heat pump as COP 4.6 and SCOP 4.65 in the same paragraph and feel inconsistent. Both are correct — they measure different things.
COP (Coefficient of Performance) is a single steady-state measurement at one outdoor / supply-water test point. The most quoted test points for residential air-to-water HPs are:
- A7/W35 — outdoor 7 °C, supply water 35 °C (mild, low-temp)
- A2/W35 — slightly cool
- A-7/W35 — design winter, low-temp
- A-7/W55 — design winter, high-temp (radiators)
A heat pump might score COP 5.0 at A7/W35 and only COP 2.5 at A-7/W55. Neither number alone tells you the annual electricity bill.
SCOP integrates COP across an entire heating season's outdoor temperature distribution, weighted by how many hours per year your climate spends at each temperature, per EN 14825. SCOP is what manufacturers report for the EU energy label.
When to use which
Use SCOP:
- For procurement decisions
- For payback calculations
- For comparing models head-to-head
Use COP:
- For sizing — peak load happens at design temperature, where COP is
worst. You need the unit to deliver enough heat there even if SCOP looks good on average.
- For diagnosing field performance — a service technician comparing
installed COP to the spec at the same test point can tell whether the unit is performing.
The ηs (eta-s) trap
The EU energy label shows ηs% (seasonal space heating efficiency in percent), not SCOP. They're related but not equal:
ηs% ≈ (SCOP / 2.5 - 0.03) × 100A heat pump with SCOP 4.5 therefore shows roughly ηs 177%, which lands you in A++ territory. The 2.5 divisor is the EU's primary energy conversion coefficient — it accounts for losses in generating and delivering the electricity that drives the pump.
Cold climate caveat
Marketing brochures love the Average climate SCOP. If you're in Helsinki, Tallinn or Trondheim, you need the Colder climate SCOP. Top-end HPs maintain Colder SCOP > 4; budget units drop to 2.5–3 because their compressors cycle and their defrost penalties pile up.
EPREL reports both numbers; our catalog defaults to Average for fair comparison, but you can filter by manufacturer and inspect the original record on each model card.