Summary

COP and SCOP are the two key performance metrics for heat pumps, but they are often misquoted and misunderstood — both by customers and by installers moving from the gas sector. A boiler has an efficiency close to 100%; a heat pump's COP is typically 2.5–4.5, making it 2.5–4.5× more electrically efficient than a direct resistance heater.

Understanding the difference between the manufacturer's peak COP, the EN 14511 test COP, and the real-world SCOP is essential for providing customers with realistic running cost estimates and for meeting MCS 007 documentation requirements.

Key Facts

  • COP (Coefficient of Performance) — instantaneous ratio: heat output (kW) ÷ electrical input (kW); measured at a specific outdoor temperature and flow temperature
  • EN 14511 — the European standard for testing heat pump performance; specifies the test conditions at which manufacturers must publish COP data (e.g., A7/W35 = 7°C outdoor air, 35°C water flow)
  • SCOP (Seasonal Coefficient of Performance) — average COP over the heating season (typically October–April in the UK); accounts for varying outdoor temperature, part-load operation, DHW, defrost cycles, and auxiliary heater use; lower than peak COP
  • ErP SCOP — the SCOP value calculated per EU Energy-Related Products regulations (EN 14825 standard); the figure used on Energy Labels; assumes a reference climate (typically 'Average' European climate); not a UK-specific value — actual SCOP in a cold Scottish location will differ from England
  • Design flow temperature effect — COP drops significantly as flow temperature increases; at -5°C outdoor and 55°C flow, COP may be ~2.0; at -5°C outdoor and 35°C flow, COP may be ~3.5; selecting the lowest achievable design flow temperature is the single biggest lever on seasonal efficiency
  • Outdoor temperature effect — COP increases as outdoor temperature rises; a heat pump operating on a mild 10°C day achieves much higher COP than on a -5°C design day; UK climate (mild winters, rare extreme cold) is favourable for ASHP efficiency
  • Defrost cycle — below approximately 5°C outdoor, frost forms on the ASHP evaporator coil; the heat pump periodically reverses the refrigerant cycle to defrost; during defrost, the heat pump briefly becomes a net heat consumer; defrost cycles reduce SCOP by approximately 5–10% in a typical UK winter
  • Running cost calculation — annual heating cost = (annual heat demand ÷ SCOP) × electricity tariff; e.g., 15,000 kWh annual heat demand ÷ SCOP 3.0 × £0.28/kWh = £1,400/year
  • SPFH (Seasonal Performance Factor for Heating) — an alternative term used in some UK documentation; equivalent to SCOP
  • MCS SCOP calculation — MCS 007 requires SCOP to be calculated and documented for the installation; typically performed using the MCS Heat Pump Calculator or Heat Engineer software; this SCOP figure is used to calculate the expected running costs for the customer

Quick Reference Table: Approximate SCOP by Design Flow Temperature (UK Climate)

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Design Flow Temperature SCOP (UK Average Climate) Running Cost vs Gas (at 28p/kWh electricity, 6p/kWh gas)
35°C (UFH, new build) 3.8–4.5 ~50% cheaper than gas
40°C (UFH, good retrofit) 3.3–3.8 ~45% cheaper than gas
45°C (large radiators) 2.8–3.3 ~35% cheaper than gas
50°C (standard retrofit) 2.3–2.8 ~25% cheaper than gas
55°C (legacy radiators) 1.8–2.3 ~10–20% cheaper than gas

Costs approximate and subject to electricity/gas tariff changes. Running cost advantage improves as gas prices rise relative to electricity.

Detailed Guidance

Understanding the COP Test Standards

EN 14511 test conditions: Manufacturers publish COP at standard test conditions. The notation system is:

  • A7/W35 — air temperature 7°C / water flow temperature 35°C
  • A2/W35 — air temperature 2°C / water flow temperature 35°C (colder outdoor, lower COP)
  • A-7/W45 — air temperature -7°C / water flow temperature 45°C (used for heating design day assessment)

A typical ASHP might show:

  • A7/W35: COP 4.5
  • A2/W35: COP 3.8
  • A-7/W45: COP 2.5

The A7/W35 figure is the most commonly quoted — and the most flattering. In practice, a UK installation running at 45°C flow (not 35°C) will achieve considerably lower COP across most of the heating season.

What SCOP includes: SCOP (per EN 14825) accounts for:

  • Part-load operation at various outdoor temperatures (weighted by how often those temperatures occur)
  • DHW heating contribution
  • Defrost cycle losses
  • Standby and controls power consumption
  • Any electric heater supplement at very low outdoor temperatures

SCOP is therefore a more realistic picture of seasonal efficiency than any single-point COP figure.

Calculating Real-World Running Costs

Step 1: Estimate annual heat demand From the BS EN 12831 design heat load and the property's degree-day data (or from an EPC energy consumption estimate):

  • Typical UK semi-detached house: 12,000–18,000 kWh/year space heating
  • DHW: add ~3,000–4,000 kWh/year for a 3–4 person household

Step 2: Apply SCOP Annual electricity consumption for heating = Annual heat demand ÷ SCOP

Example:

  • Annual space heating demand: 14,000 kWh
  • DHW: 3,500 kWh
  • Total heat demand: 17,500 kWh
  • SCOP: 3.0 (at 45°C DFT)
  • Annual electricity for heating: 17,500 ÷ 3.0 = 5,833 kWh
  • At £0.28/kWh: 5,833 × £0.28 = £1,633/year

Compare to gas:

  • Gas boiler efficiency 90%: 17,500 ÷ 0.9 = 19,444 kWh gas
  • At £0.06/kWh: 19,444 × £0.06 = £1,167/year

At current tariffs (2026), the heat pump example above is more expensive than gas. This is because the electricity/gas price ratio in the UK is approximately 4:1–5:1. A SCOP of 4.0+ (achievable with UFH at 35°C DFT) would reverse the comparison. Customers must understand this — a heat pump at 55°C DFT with a SCOP of 2.2 may cost more to run than the gas boiler it replaces.

Managing customer expectations:

  • Provide a SCOP estimate based on the actual design flow temperature and UK climate
  • Calculate a running cost estimate for both heating and DHW
  • Be honest about the electricity/gas price ratio — the customer's running cost benefit depends entirely on SCOP × tariff ratio
  • Reference the BUS grant (£7,500) as the primary financial incentive, not running cost savings at current tariffs

SCOP in MCS Documentation

MCS 007 requires the SCOP to be calculated and recorded in the design documentation. The MCS Heat Pump Calculator produces this value. Heat Engineer software also generates an MCS-compliant SCOP figure.

The SCOP value should be calculated for the specific installation (design flow temperature, property location, annual heat demand split between space heating and DHW). Using the manufacturer's ErP SCOP directly (without adjusting for UK climate and actual DFT) may overstate expected performance.

Improving SCOP: The Practical Levers

  1. Lower the design flow temperature — the most impactful lever; moving from 55°C to 45°C DFT typically improves SCOP by 0.6–1.0; requires correctly sized emitters
  2. Weather compensation — running the heat pump at a lower flow temperature on milder days; should always be enabled; typically adds 0.2–0.5 to SCOP vs fixed flow temperature
  3. Correct sizing — a correctly sized heat pump runs longer and avoids short-cycling; short-cycling degrades SCOP due to frequent start-stop losses
  4. Minimising DHW setpoint — heating DHW to 50°C rather than 60°C reduces the COP penalty; weekly 60°C pasteurisation cannot be avoided but the daily setpoint can be kept low
  5. Time-of-use tariff — running the heat pump during cheaper-tariff hours does not improve SCOP but reduces cost-per-unit of heat output

Frequently Asked Questions

My customer's heat pump shows a COP of 5.8 on the controller display. Is this accurate?

Possibly not. Heat pump controllers typically calculate COP from the temperature difference across the heat exchanger (measured by the heat pump's internal sensors) and the compressor power consumption. This measurement is often inaccurate — particularly when defrost cycles are excluded, when the pump power is not included, or when sensor accuracy is poor. An independently measured SCOP using a calibrated heat meter and electricity meter over a full season is the only reliable figure. The manufacturer's EN 14511 data and MCS-calculated SCOP are better references than the controller display.

Does the heat pump's rated COP guarantee that SCOP?

No. COP is measured at specific test conditions. SCOP depends on how the system is designed, installed, and operated. A heat pump rated at COP 4.5 at A7/W35 may achieve only SCOP 2.8 in a property where the DFT is 55°C, the system short-cycles, and weather compensation is disabled. The installation design has more impact on SCOP than the heat pump's rated COP.

What SCOP should I quote to a customer?

Use the MCS Heat Pump Calculator or Heat Engineer software to calculate SCOP for the specific installation. As a rough guide: SCOP 2.8–3.2 for a typical 45°C DFT retrofit; SCOP 3.5–4.2 for a well-designed 35–40°C DFT system. Never quote the manufacturer's peak COP — it is not the seasonal efficiency figure.

Regulations & Standards