COP, SCOP and SPF: how to read a heat pump performance estimate

What to know first

These points explain which number matters in a quote and why it remains an estimate.

COP, SCOP and SPF all express heat delivered for each unit of electricity used, but they answer different questions. For a household quote, the estimated seasonal performance factor is normally more useful than a brochure COP. Read it with the annual electricity estimate and its assumptions.

This article mainly covers air-to-water systems serving radiators or underfloor heating. The Microgeneration Certification Scheme (MCS) uses a hydronic, or water-based, estimate standard for these systems. It has a separate standard for air-to-air heat pumps. The standards were checked on 18 August 2026.

COP, SCOP and SPF: the difference at a glance

This table is a starting point. The label alone is not enough: the test conditions, calculation assumptions and system boundary matter too.

MCS defines COP at a specific temperature condition and SCOP across a designated cold, average or warm climate season. A COP of 4 means four units of heat per unit of electricity at that condition; it does not promise an in-home SPF of 4.

For SPF, ask what is inside the boundary? Monitoring studies may report the heat pump unit alone. A broader result can include backup heat, an immersion heater and a circulation pump. Those boundaries produce different numbers from the same installation.

MCS puts this warning on its consumer estimate:

Start with the MCS estimate, not the brochure COP

For an MCS-certified hydronic installation, the standard estimate must be provided before the contract is awarded. It uses annual heating and hot-water demand, floorspace, postcode climate data, proposed heat emitters such as radiators, and flow temperature. It then gives an estimated SPF and annual electricity range in kilowatt-hours (kWh).

Check that it states the demand the heat pump will supply, proposed emitters, flow temperature, indicative capacity, estimated SPF and annual kWh. A hybrid quote should also show the share intended to come from the heat pump.

The output displays a range 10% below to 10% above calculated use. Yet MCS also says predictions can reasonably vary by around 25–30% in many cases, and sometimes more. The cautious interpretation is that the displayed ±10% is a calculation range, not a guarantee.

Good to know

Indicative capacity can change after a room-by-room heat-loss assessment and final design. Check whether the estimate uses that assessment or mainly Energy Performance Certificate data.

Why climate and flow temperature change the result

An air source heat pump takes heat from outdoor air. It raises that heat to the temperature needed by the heating system. Colder air and hotter heating water increase the temperature gap. The compressor generally works harder, so efficiency can fall.

Flow temperature is the temperature of water leaving the heat pump for the radiators or underfloor heating. Larger radiators, suitable underfloor heating and lower heat loss can allow cooler water. The correct setting is a design outcome, not a number to reduce without checking room heat output.

The current MCS lookup method illustrates the relationship. For an air source heat pump, it uses an estimated space-heating SPF of 4.0 up to 35°C. It uses 3.4 at 41–45°C, 3.1 at 46–50°C and 2.5 at 56–65°C. These are method values, not promises for every home.

Where existing radiators are retained with few or no enlargements, MCS uses a default 60°C unless a room-by-room calculation justifies less. A 45°C quote is credible only if the proposed emitters can provide enough heat at that temperature.

Expert insight

“A high brochure COP can sit beside a more modest home estimate. The first describes the unit at a test point; the second must allow for the property and wider system.”

Giles Crosse

Energy Editor

Experienced editor, journalist and communications consultant specialising in consumer energy and low carbon technologies.

• Editor and campaign author for Shell, EDF Energy and Good Energy.
• Consultant to the United Nations and contributor to the World Economic Forum.
• Journalist for Reuters, the BBC, The Economist and The Guardian.

More about Giles Crosse

How hot water and backup heat affect the figure

Hot water normally needs a higher temperature than space heating. It should not simply use the space-heating SPF. Under MCS 031 a Issue 2.0, the air source heat pump estimate divides annual hot-water demand by 1.9. It separately adds expected immersion-heater electricity for pasteurisation, a periodic high-temperature cycle used to control bacteria.

Electric resistance backup heat does not multiply its electricity input as a heat pump does, so it can reduce a broad whole-system SPF. For a hybrid, the quote should state how much demand the heat pump will supply. Its SPF should not be presented as the efficiency of the combined system.

Good to know

Check whether annual electricity includes hot water, cylinder pasteurisation, backup heat and circulation pumps. Without that scope, it is not a complete whole-system estimate.

Controls and household demand are different issues

Weather compensation adjusts flow temperature as outdoor conditions change, helping to avoid hotter water than needed. MCS identifies sizing, flow and return temperatures, emitters and controls as design factors affecting efficiency.

A warmer thermostat, more hot-water use, longer occupancy or open windows may instead increase the heat required. Consumption can rise even if SPF is unchanged. MCS separates “energy required” from “system efficiency” for this reason.

Energy Systems Catapult’s Richard Halsey said in 2024 that “when designed and installed well, heat pumps can be an effective low carbon heating solution”.

What measured performance tells us

Measured SPF describes an installed system, not what another home will achieve. Energy Systems Catapult’s interim analysis reported a median air source heat pump SPFH4 of 2.80 across 291 systems. SPFH4 was the project’s broad boundary, including backup and immersion heat plus circulation-pump electricity. The middle half of results ran from 2.53 to 3.09. The study also found a general trend of higher SPF at lower mean flow temperatures.

On the coldest operating day, the median broad-boundary COP was 2.44 across 484 systems. The report identified the mean outdoor temperature as −0.4°C. This shows cold weather can reduce efficiency without making the heat pump equivalent to direct electric heating. It does not predict an individual result.

The wider project installed 742 heat pumps across varied British homes, but every property still required design and installation decisions.

How to compare two heat pump performance estimates

Use these checks before comparing headline figures.

1. Match the metric and boundary. Compare COP at the same conditions, SCOP for the same application and SPF with the same equipment included.

2. Match the heat demand. Different annual demand assumptions produce different electricity estimates even at the same SPF.

3. Test the flow-temperature claim. Ask what emitter design and room-by-room heat-loss calculation support it.

4. Check climate and hot water. The MCS hydronic method uses postcode climate data and separately treats hot-water demand.

5. Read annual kWh, not only SPF. Running cost also depends on the tariff and when electricity is used, so neither figure guarantees savings.

6. Question unusually strong alternatives. MCS allows other software forecasts, but they must not outrank its standard estimate and need a warning if significantly better.

MCS warns that different heating technologies use different estimate methods and should not be compared one-to-one. Compare energy, price and scope assumptions rather than unlike headline numbers.

When professional input may be useful

A room-by-room heat-loss assessment and emitter design turn a pre-sale indication into a property-specific design. An MCS-certified installer or qualified heating designer should explain the assumptions, expected heat-pump share and backup operation. An independent assessor may help if the Energy Performance Certificate no longer reflects the property.

Key takeaways

• COP is a snapshot; SCOP is a standardised product season; SPF is a seasonal system measure.

• An SPF in a quote is predicted. A measured SPF needs suitable meters and a defined boundary.

• Lower flow temperatures generally support efficiency, but emitters must still heat every room.

• Hot water, immersion heaters, backup heat and pumps can change a whole-system result.

• Read the MCS annual kWh and assumptions, not the brochure COP alone.

• No estimate guarantees electricity use, cost or savings.

Frequently asked questions