Heat Pump COP and SCOP Explained for Landlords

The short answer

COP and SCOP both measure how much heat a heat pump gives out for each unit of electricity it uses. COP (coefficient of performance) is a snapshot under one set of test conditions. SCOP (seasonal coefficient of performance) is the average over a whole year. SCOP is the figure that sets the tenant’s bill, so it is the one to ask for.

A SCOP of 3.0 means 3kWh of heat for every 1kWh of electricity over a year. The MCS design standard for heat pumps, MIS 3005-D, uses that same example in the Key Facts it requires installers to give customers.

COP: a snapshot

A COP describes one moment: one outdoor temperature and one water temperature. A heat pump making warm water on a mild day has a high COP. The same unit making hot water on a frosty morning has a much lower one.

That is why a single COP printed in a brochure tells a landlord little about the bill. It is a lab figure, useful for comparing products under identical conditions and not much else.

SCOP: the year, and the bill

SCOP spreads performance across a standard heating season. MIS 3005-D describes the MCS SCOP as a theoretical indication of efficiency over a whole year using standard climate data, not local data, and says it is used to compare heat pumps under fixed conditions. It also says the estimate is guidance only and not a guarantee.

For a landlord, two points follow:

• The SCOP an installer quotes depends on the design flow temperature, the temperature of the water sent to the radiators. A lower flow temperature gives a higher SCOP.
• Real homes often do worse than the design figure. In the Electrification of Heat demonstration project, analysed by Energy Systems Catapult for the government, the measured seasonal performance was below the design SCOP in 91.9% of homes, by 0.66 on average. The median measured result for 428 air source heat pumps was 2.93.

Break-even SCOP against gas: the arithmetic

The question for a gas heated rental is simple: at what SCOP does the heat pump cost the same to run as the boiler?

Use the Ofgem price cap unit rates for 1 October to 31 December 2026: electricity 26.32p per kWh, gas 7.97p per kWh. Assume a gas boiler at 90% efficiency.

1. Cost of 1kWh of heat from gas: 7.97p divided by 0.9 = 8.86p.
2. Cost of 1kWh of heat from a heat pump: 26.32p divided by SCOP.
3. Set them equal: 26.32 divided by SCOP = 8.86, so SCOP = 26.32 divided by 8.86 = 2.97.

Below a SCOP of about 2.97 the heat pump costs more to run than the boiler. Above it, less. Electricity carries no VAT from 1 October 2026 to 31 March 2027, while gas carries 5%; both are already in the cap rates above. If prices change, rerun the same three steps with the new unit rates. Standing charges are left out; if the gas supply is removed altogether, the gas standing charge of 29.68p a day, about £108 a year, also stops.

Worked example (modelled, not a real project)

Inputs: a three bedroom semi needing 12,000kWh of heat a year (the illustrative figure used across this site), the cap unit rates above, gas boiler at 90%. Standing charges left out. Rounded.

System	Electricity or gas used	Yearly cost
Gas boiler, 90%	13,333kWh gas	£1,063
Heat pump, SCOP 2.5	4,800kWh	£1,263
Heat pump, SCOP 2.93 (measured median)	4,096kWh	£1,078
Heat pump, SCOP 2.97 (break-even)	4,040kWh	£1,063
Heat pump, SCOP 3.0	4,000kWh	£1,053
Heat pump, SCOP 3.5	3,429kWh	£902
Heat pump, SCOP 4.0	3,000kWh	£790

Each step of 0.5 in SCOP moves the tenant’s bill by more than £100 a year in this example (from about £112 to £210). That is why the design detail matters more than the brand of unit.

What raises or lowers SCOP

Flow temperature is the largest lever. In the same Energy Systems Catapult report, the median measured COP across all heat pumps was 3.50 when producing water at 35°C, 2.38 at 55°C, and 2.02 above 65°C.

A lower flow temperature needs larger radiators, because cooler water gives out less heat per radiator. Radiators sized for a hot gas boiler are often too small. Other factors include hot water settings, controls left on weather compensation, and whether the unit was sized from a proper heat loss calculation rather than the old boiler’s output.

What to ask an installer for

The MCS design standard, MIS 3005-D Issue 3.0 (mandatory for MCS contractors from 5 December 2025), sets out what customers must be given. Before the contract is awarded, the installer must give a performance estimate, the heat pump’s datasheet and, where a cylinder is proposed, its datasheet. Before installation starts, the customer must be given in writing:

• every room’s specific heat loss (in W/m²), from a heat load calculation to BS EN 12831-1:2017
• the design flow temperature of the water leaving the heat pump
• the installation’s SCOP at that flow temperature
• the type and size of each radiator or emitter
• the daily hot water demand and any new cylinder’s specification

Where a design proposes a flow temperature above 55°C, the standard says an alternative design at 55°C or lower should also be offered, with the difference in efficiency explained. Use that clause: ask for the lower temperature option and compare the SCOP.

Check the installer is MCS certified yourself on the MCS register; certification is also needed for the Boiler Upgrade Scheme grant. A longer list of questions is in questions to ask a heat pump installer.

When SCOP is not the deciding number

• Direct electric heating. Against panel heaters at 26.32p per kWh, any SCOP above 1 saves money, and SCOP 3.0 uses about a third of the electricity.
• A home that needs fabric work first. A poor SCOP is often a symptom of high heat loss. Insulation can raise SCOP and lower the size of unit needed.
• Time of use tariffs. A cheaper overnight or heat pump tariff changes the electricity price in step 2. Rates vary by supplier, so use the actual tariff, not the cap.

Next step

Put a quoted SCOP and your own heat demand into the heat pump landlord calculator. If you want a design to compare, send an enquiry through the quote page and relevant independent firms contact you, with no charge to you and no obligation.

Prices and figures were read from the sources listed on 8 October 2026. This is general information, not financial advice.