COP and SCOP Explained: What the Numbers Mean, How to Calculate Seasonal Performance and Customer Expectations

Quick Answer: COP (Coefficient of Performance) is the ratio of heat output to electrical energy input at a specific set of conditions. A COP of 3.0 means 1kWh of electricity produces 3kWh of heat. SCOP (Seasonal COP) is the average COP over a full heating season, accounting for varying outdoor temperatures and DHW demand — it is the figure that determines annual running costs and is the value quoted in MCS documentation. A typical UK ASHP achieves SCOP 2.8–3.8 depending on design flow temperature and climate zone.

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

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:

A typical ASHP might show:

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:

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):

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

Example:

Compare to gas:

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:

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