Smarter Heating & Hot Water

Advice

Heat pump terminology

Four efficiency words that get used as if they were the same number. They are not. COP is a snapshot. SCOP is a lab seasonal rating. SPF is a seasonal figure for a system — on an MCS quote it is an estimate, in a monitored house it is a measurement.

The hub page treated SPF as “actual, no external pumps” and SCOP as “the same thing plus external pumps, also called SPF (actual)”. That mix is not how MCS or EN 14825 use the words. The four headings below keep the hub’s terms and put the boundaries back.

COP — coefficient of performance

COP is heat delivered divided by electrical input at one test condition. It is a steady-state rating, not a year. The hub’s example is the usual shape: heat at about 45 °C flow with about 7 °C outside, divided by the electricity the unit is drawing at that point. Datasheets quote several COPs (A7/W35, A7/W55, and so on). A high COP at 35 °C flow says nothing about the same machine at 55 °C.

For running-cost comparisons you need a seasonal number, not a single COP. The COP breakeven calculator is the unit-rate test against a gas boiler.

SCOP — seasonal coefficient of performance

SCOP is the calculated seasonal figure for the heat pump unit under BS EN 14825. MCS 007 (the product standard) defines it as the reference annual heating demand divided by the annual energy consumption for heating, for a designated climate zone — cold, average or warm. UK ErP labels use the average zone. It is a modelled kWh/kWh, not last winter’s meters.

The calculation uses part-load tests and includes some of the unit’s own electrical overheads in the standard (standby, crankcase heater, and the fans or pumps that belong to the appliance). It is not a survey of your radiators, your pipework, or your backup immersion. Fuel-driven heat pumps use an equivalent called SPER (seasonal primary energy ratio).

SPF — seasonal performance factor

MCS 031 (the pre-sale calculation for a hydronic install) uses SPF for the system over a season: heat delivered divided by the electrical energy consumed over that period. A guide figure of SPF 3 means 3 kWh of heat per 1 kWh of electricity over a standard year. On an MCS quote that SPF is estimated from heat loss and the product SCOP tables — it is not a promise of next year’s bill.

When someone has actually metered a house, SPF is also the name for that measured ratio. The SEPEMO paper MCS points at for hot-water products splits system boundaries (H1–H4): whether you count only the compressor and its controls, or also source pumps, backup heaters, and heating-circuit pumps. Always ask which boundary a measured SPF used. The hub’s “controller in, external pumps out” line is one possible boundary, not the definition of SPF.

System efficiency

This is the widest of the four. The hub had it as the complete system: the heat pump, ground collectors on a GSHP, fans, emitters, and controls. It is the number that moves when the radiators are too small, the flow temperature is too high, the cylinder coil is undersized, or the backup heater runs. SCOP on the box will not show that. Design and commissioning will.

Which figure to read

Related

Guidance only. COP, SCOP and SPF wording checked against public MCS 007 v8 and MCS 031-a (2025) and the scope of BS EN 14825. Product tables and climate bins move — use the live MCS product listing for a certificate figure. This is not a design or a running-cost guarantee.