SCOP performance estimate

SCOP, the SCOP, is an estimate of heat delivered for each unit of electrical energy over a defined heating season. It is more useful for annual planning than a single-point COP, but it is still a modelled value with a specified test and calculation boundary.

A SCOP estimate helps compare designs and estimate annual electricity. It does not prove the peak capacity of a heat pump and must not be used to size one.

SCOP, COP and SPF are different

COP is the ratio of heat output to electrical input at a stated operating point. It is meaningful only with the source temperature, leaving-water temperature, flow conditions and test boundary attached.

SCOP combines performance across a defined set of seasonal conditions and loads. It allows for different operating points rather than treating one COP as though it applied all year.

SPF, the seasonal performance factor, normally describes measured or calculated whole-system performance over a period. Its value changes with the boundary. A figure covering only the heat-pump unit is not directly comparable with one that includes circulation pumps, controls, immersion heating or backup energy.

The terms should not be swapped casually. A high laboratory COP at mild conditions does not establish the annual performance of the installed system.

The MCS pre-sale estimate

As at 22 July 2026, MIS 3005-D Issue 3.0 and the MCS 031 pre-sale calculation set the relevant MCS framework. For an eligible domestic property, the standard route uses a valid EPC with the MCS 031 method and the applicable MCS product performance data.

The estimate considers space-heating demand, hot-water demand, the proposed emitter arrangement, flow temperature and the relevant seasonal efficiency. It then reports estimated electricity use and the required customer information.

Where a valid EPC or suitable SCoP cannot be used, MIS 3005-D provides an alternative method. The annual heat load must be calculated by a suitable justified method, multiplied by the proportion to be provided by the heat pump and divided by the applicable seasonal efficiency. Energy from supplementary heat is calculated separately.

An installer may provide an additional model from proprietary software. MIS 3005-D says the approach and factors must be described and justified, it must not be given greater prominence than the standard MCS estimate, and a materially better result must carry a warning that it should be treated with caution.

Annual heat and peak heat are separate

Annual heat demand is measured in kWh. Peak design heat load is measured in kW. Dividing annual heat by SCOP estimates annual electricity; it does not reveal how much output the unit can produce during the cold design condition.

The simplified relationship is:

annual heat-pump electricity = annual heat supplied by the heat pump ÷ seasonal efficiency

This is valid only when the numerator and efficiency use compatible services and boundaries. It must not include heat that will actually come from an immersion heater or another heat source unless that energy is separately represented.

Heat-pump sizing instead uses the BS EN 12831 design load and the unit’s output at the design outdoor and flow temperatures.

Flow temperature changes the estimate

The space-heating SCoP used in the design must match the proposed design flow temperature and emitter arrangement. Higher water temperatures generally make the heat pump work harder, but the size of the effect is product-specific.

MIS 3005-D requires the design information to state the installation’s SCoP or SPER from the MCS data based on the design flow temperature. It also requires the leaving-water temperature before any blending valves. Using a lower blended underfloor temperature to represent a heat pump that must produce hotter water would overstate performance.

Weather compensation can improve seasonal operation by reducing the target temperature in milder weather. The estimate still needs a defensible cold-weather design point and emitter schedule.

Keep space heating and hot water separate

Domestic hot water usually requires a higher water temperature than space heating and has different standing losses and usage patterns. The calculation should distinguish:

• electricity for space heating
• electricity for cylinder charging
• immersion or pasteurisation energy
• supplementary or backup heat
• auxiliary energy included or excluded by the method

Combining these into one undocumented efficiency number makes it impossible to compare the prediction with later monitoring.

Why real performance can differ

The estimate cannot know future weather or household behaviour. Installed performance is affected by:

• actual indoor temperatures and heating hours
• the final weather-compensation curve
• flow and return temperatures
• cycling at low load
• defrost conditions for an air-source unit
• hydraulic separation and mixing
• circulation-pump and control energy
• hot-water set points and draw-off
• immersion and supplementary-heater operation
• changes to the building fabric or ventilation

These are reasons to state assumptions and a sensible range, not reasons to replace the standard result with an anecdotal SCOP.

Performance-estimate assumptions

Two SCOP estimates are comparable only where the underlying service, temperature and measurement boundary match. The calculation inputs include:

• the exact heat-pump model and product-data source
• the design outdoor, flow and return temperatures
• the emitter type or mix used by the method
• annual space-heating and hot-water demand inputs
• electricity for space heating, hot water and immersion separately
• the proportion of heat assigned to any other source
• treatment of pumps and auxiliaries
• the standard method and any alternative calculation

Running-cost comparisons need clearly stated tariff assumptions. Annual kWh keeps the technical result separate from a live unit price. Any price used in the calculation needs a date and remains an input rather than a forecast.

Checking the installed system later

Meaningful monitoring needs both heat delivered and electricity consumed over the same period and boundary. Controller estimates can help identify trends, but they are not necessarily equivalent to calibrated metering.

Comparison with the pre-sale estimate should account for weather, room temperature, hot-water use and the included electrical loads. A difference does not by itself diagnose a faulty heat pump, although persistent high flow temperature, direct-electric use or cycling can explain poor results and should be investigated.

Related entries

• Heat loss survey
• Design flow temperature
• Heat pump sizing margin
• Weather compensation controls
• Monitoring portal data
• Commissioning flow rates