COP is a heat pump's instantaneous efficiency at one test point — heat out divided by electricity in; COP 4.0 means 4 kWh of heat per 1 kWh of electricity. SCOP is the seasonal average calculated under the EN 14825 test cycle for a standard climate year. SPF is the same ratio actually measured in a running installation — the only one of the three that determines your bill.
What is COP and what does it actually tell you?
COP — coefficient of performance is the ratio of heat delivered to electricity consumed at a single, laboratory-defined operating point, always quoted with its conditions: A7/W35 means 7 °C outdoor air and 35 °C water flow temperature. A COP of 4.0 at A7/W35 says the machine moved four units of heat per unit of electricity in mild weather into a low-temperature circuit — it says nothing about February at 55 °C flow. That is why the same heat pump carries many COP values: Solimpeks' Varm Up series, for example, lists heating COP ranges between 4.23 and 4.92 across its models at A7/W35 rating conditions, and each model's COP shifts across its own capacity range. COP is a like-for-like snapshot for comparing hardware, not a promise of annual performance.
What is SCOP and how is it measured?
SCOP — seasonal COP answers the obvious objection to COP: weather changes. Under EN 14825, the heat pump is tested at several outdoor temperatures and part-load ratios, and the results are weighted across a standardised heating season (the EU 'average' climate profile is based on Strasbourg, with 'warmer' and 'colder' profiles for Athens and Helsinki). The weighted result is the SCOP printed on the energy label, and dividing it into primary-energy terms gives the seasonal space heating efficiency ηs that EU Ecodesign regulation 813/2013 uses to set minimum efficiency and label classes. SCOP is far more honest than COP — but it still assumes a standard climate, a standard load curve and a correctly designed system.
What is SPF, and why is it the number that matters?
SPF — seasonal performance factor, known in Germany as JAZ — is measured, not calculated: heat meter reading divided by electricity meter reading over a real year in a real house, usually including circulation pumps, controls and backup heater. It captures everything the laboratory cannot: your climate, your radiators, your flow temperature, your hot water habits and your installer's design choices. Field monitoring campaigns in Germany (Fraunhofer ISE) have measured average SPFs around 3.1 for air-source heat pumps in existing buildings — respectable, but visibly below the SCOPs of the same machines, and the gap is almost always system design rather than the machine itself.
COP vs SCOP vs SPF at a glance
| Metric | What it measures | Where it comes from | Where you find it |
|---|---|---|---|
| COP | Efficiency at one test point (e.g. A7/W35) | Laboratory rating test | Datasheet |
| SCOP | Modelled seasonal efficiency, standard climate | EN 14825 test cycle | Energy label, ErP documentation |
| SPF (JAZ) | Real measured annual efficiency, whole system | Heat and electricity meters on site | Your installation's monitoring |
Why doesn't the quoted COP match my energy bill?
Because your bill is made by the SPF, and SPF is dragged down by everything between the datasheet and your radiators: flow temperatures above design, oversized machines short-cycling, poorly set weather compensation, backup heaters covering design errors and hot water runs at 55 °C+. As a rule each 1 °C reduction in flow temperature improves efficiency by roughly 2–3%, which is why commissioning matters as much as hardware. If your measured numbers disappoint, work through why is my heat pump COP so low; if you want to raise the source side instead, warmer source temperatures from solar — the solar-assisted heat pump approach — lift COP by roughly 2–3% per kelvin of source gain (IEA SHC Task 60). And when comparing running costs against gas, the break-even arithmetic lives in at what COP a heat pump beats a gas boiler.
Frequently asked questions
Is a higher COP always better when comparing heat pumps?
Only when quoted at identical conditions — a COP at A7/W35 cannot be compared with one at A2/W35 or A7/W45. Compare SCOP for the right climate zone, and check the COP at the coldest realistic condition for your region, not just the headline figure.
What is a good SPF for an air source heat pump?
Well-designed installations achieve SPFs of 3.5 or higher; German field studies average around 3.1 in existing buildings, and values below about 2.5 usually indicate design or commissioning problems rather than a faulty machine. Low flow temperatures and correct sizing are the biggest levers.
Does SCOP include domestic hot water?
No — SCOP under EN 14825 covers space heating only. Hot water performance is rated separately under EN 16147 with tapping-cycle profiles, and because DHW requires higher temperatures it always shows lower efficiency than the space heating figures.
What is JAZ on a German heat pump report?
JAZ (Jahresarbeitszahl) is simply the German term for the measured seasonal performance factor — annual heat output divided by annual electricity input. German subsidy and monitoring practice leans heavily on JAZ, which is why it appears in reports and grant paperwork.