SCOP explained: what the seasonal figure means for a commercial heat pump
SCOP is the efficiency number that decides whether a heat pump saves energy cost; this guide explains how it is rated, why your site will differ, and how to check a quote.
COP, SCOP and SEER in one paragraph each
COP (coefficient of performance) is heat delivered divided by electricity used at one fixed operating condition, for example a stated outdoor temperature and a stated water temperature. It is a snapshot.
SCOP (seasonal coefficient of performance) is the same ratio averaged over a heating season using a defined profile of outdoor temperatures and load. Because real operation spans mild and cold days, part load and defrosting, SCOP is the number to use when estimating annual energy use.
SEER (seasonal energy efficiency ratio) is the cooling-side equivalent, used when a reversible unit also provides cooling. This guide focuses on heating, so SEER is mentioned only for completeness.
What a rated SCOP assumes
Seasonal figures for heat pumps are rated using the method in BS EN 14825, which sets out test conditions and a calculation method for part-load and seasonal performance. A rated SCOP is calculated for a stated reference climate, for stated flow temperature conditions (low-temperature and medium-temperature applications are rated separately), and for the unit’s own power consumption in the modes the standard covers. It does not describe your building. It is a way of comparing machines on the same basis.
That is why a datasheet SCOP is only meaningful alongside the flow temperature it was rated at. Compare like with like, and be cautious of a headline figure quoted at a low flow temperature when your emitters need a hotter one. The high-temperature heat pump guide covers that trade-off.
Why your site SCOP will differ
- Flow temperature. The single biggest lever. Lower flow temperature means a smaller temperature lift and a higher SCOP.
- Weather compensation. Controls that lower the flow temperature as it gets milder keep the unit working in its efficient range. Fixed high flow temperature all year loses that benefit.
- Defrost. Air-source units periodically defrost the outdoor coil in cold, damp weather, which consumes energy and interrupts heating.
- Auxiliary loads. Circulation pumps, buffer and cylinder immersion back-ups, trace heating and controls use electricity that a unit-level rating may not include.
- Hot water. Heating water to storage temperature is generally less efficient than space heating at low flow temperature.
- Hybrid operation. If a boiler takes the coldest hours, the heat pump runs on milder days when it is more efficient; see hybrid retrofit.
- Commissioning and maintenance. Poor control settings, dirty coils and badly balanced circuits all reduce performance.
None of this is a reason to distrust SCOP; it is a reason to treat the rated figure as a starting point and to ask the designer how the site figure was estimated.
How to read the SCOP on a quote
- Find the flow temperature the SCOP was rated at. If it is not stated, ask.
- Check whether it is the unit’s rated SCOP or a system-level estimate for your building, and what assumptions sit behind the estimate.
- Ask which loads are included: pumps, back-up heaters, hot water.
- Ask what happens at design-day temperature: what output the unit delivers, and what covers the remainder.
- Ask what metering will be fitted so the figure can be checked in operation.
Why “SCOP must exceed X to beat gas”
Cost per kWh of heat equals the energy price divided by efficiency. For a heat pump that efficiency is the SCOP; for a gas boiler it is its seasonal efficiency. Setting the two costs equal gives a break-even SCOP: electricity price divided by (gas price divided by boiler efficiency).
DESNZ Quarterly Energy Prices for Q1 2026 (provisional, published 30 June 2026, excluding VAT, including Climate Change Levy) give medium-sized businesses an average of 25.0p per kWh for electricity and 4.55p per kWh for gas. Assuming an 88% boiler efficiency, gas heat costs 4.55 ÷ 0.88 = about 5.17p per kWh of heat. Break-even SCOP = 25.0 ÷ 5.17 = about 4.8. A system with a SCOP below that costs more per kWh of heat than gas at those average prices.
The result moves with your own tariffs. A cheaper negotiated or time-of-use electricity tariff, on-site generation, a higher gas price or a need for cooling all change the answer. One published installer guide uses a different gas price assumption and reports roughly 7.5p per kWh of heat at a COP of 3.2 and 24p per kWh electricity against 7-8p for a gas boiler. Use the running-cost calculator with your own prices.
What to monitor after install
The only way to know your site SCOP is to measure it. Ask for a heat meter on the heat pump’s output and an electricity sub-meter on its input (including pumps and back-up heaters if you want a system figure), with data you can read. Divide heat delivered by electricity used over the season. If the figure is well below the design estimate, flow temperature, weather-compensation settings and defrost behaviour are the first places to look. Include metering in the specification when you compare quotes, as the cost guide suggests.