The UK default heat pump flow temperature is 55°C
Most UK heat pumps are installed with a default flow temperature of 55°C, a legacy from gas boiler system design. This setting is often higher than necessary for efficient heat pump operation. Lowering the flow temperature can substantially reduce your electricity bills.
For every 1°C reduction in flow temperature, a heat pump’s Coefficient of Performance (CoP) can improve by approximately 2–3%, according to the Energy Saving Trust (Energy Saving Trust, 2026). The CoP is the ratio of heat output to electricity input: a CoP of 3 means three units of heat for every unit of electricity. Data from the Department for Energy Security and Net Zero (DESNZ) Electrification of Heat Demonstration Project (2023) showed average system flow temperatures in UK installations were around 50–55°C (DESNZ, 2026). Operating at 45–50°C instead of 55°C reduces the temperature lift the compressor must achieve, directly cutting electricity consumption.
Flow temperature directly determines your heat pump’s Coefficient of Performance (CoP) and running cost
Ofgem’s Renewable Heat Incentive (RHI) data showed average CoP for air-source heat pumps in UK homes was 2.8–3.2 at 55°C flow temperature (Ofgem, 2026). The Microgeneration Certification Scheme (MCS) installation standards require CoP calculations at specific flow temperatures (MCS, 2026).
A drop from 55°C to 45°C flow temperature can improve CoP from approximately 2.8 to around 4.0, cutting electricity use by roughly 30%. For a typical 3-bed semi-detached home (based on ONS housing stock data), this could save £200–£350 per year compared to a 55°C setting. The exact saving depends on your home’s heat demand, local electricity tariff, and how low you can safely set the flow temperature.
Quick numbers flow temperature, CoP, and annual cost comparison for a UK home
| Flow temperature | Typical CoP range | Annual electricity consumption (kWh) | Annual cost at 28p/kWh | Estimated annual saving vs 55°C |
|---|---|---|---|---|
| 35°C | 4.5 – 5.0 | 2,800 – 3,200 | £784 – £896 | £400 – £500 |
| 40°C | 4.0 – 4.5 | 3,200 – 3,600 | £896 – £1,008 | £300 – £400 |
| 45°C | 3.5 – 4.0 | 3,600 – 4,000 | £1,008 – £1,120 | £200 – £300 |
| 50°C | 3.0 – 3.5 | 4,000 – 4,400 | £1,120 – £1,232 | £100 – £200 |
| 55°C | 2.8 – 3.2 | 4,400 – 4,800 | £1,232 – £1,344 | , |
CoP ranges are based on Energy Saving Trust heat pump performance data and DESNZ Electrification of Heat project findings. The electricity cost uses the Ofgem price cap default tariff rate for direct debit customers, January 2026 (Ofgem, 2026). Annual consumption assumes a typical 3-bed semi-detached home with a heat demand of approximately 10,000 kWh per year.
Your home’s heat loss determines the minimum flow temperature you can use
A lower flow temperature requires larger radiators or underfloor heating to deliver the same heat output. The Energy Saving Trust’s heat loss calculation guidance states that a room-by-room heat loss calculation is essential for correct heat pump sizing (Energy Saving Trust, 2026). Radiators must be sized for 45°C flow temperature, not the 70–80°C typical of gas boilers. The Chartered Institution of Building Services Engineers (CIBSE) Guide B1 provides radiator output derating factors for lower flow temperatures (CIBSE, 2026).
Homes with poor insulation (single glazing, uninsulated walls, draughty loft) may need 55°C flow to meet heat demand on cold days. This reduces potential efficiency gains. Improving insulation before installing a heat pump allows you to use a lower flow temperature and achieve better CoP. How to improve home insulation for heat pumps
The UK’s 2026 Boiler Upgrade Scheme (BUS) grant requires MCS-certified installation with a recorded flow temperature
The Boiler Upgrade Scheme (BUS) offers a grant of £7,500 for air-source heat pumps and requires MCS certification (GOV.UK, 2026). The MCS installation standard MIS 3005 requires the installer to record the design flow temperature and verify it during commissioning (MCS, 2026). The installer must provide a system design showing the chosen flow temperature and how it matches your home’s heat loss and emitter sizing.
If the recorded flow temperature is above 55°C, it may indicate poor system design (e.g., undersized radiators or insufficient insulation). The BUS does not penalise this, but your running costs will be higher. Ask your installer to justify any flow temperature above 50°C in writing before you proceed.
Adjusting your heat pump’s flow temperature is a simple control change
Heat pump manufacturer manuals (e.g., Daikin, Mitsubishi Electric, Vaillant) explain how to change the flow temperature via the controller. The flow temperature can usually be adjusted in 1–5°C increments. The “weather compensation” curve sets the flow temperature automatically based on outdoor temperature, improving efficiency by reducing flow temperature when it is milder outside (Energy Saving Trust, 2026).
Incorrect adjustment (setting too low) can cause your home to not reach the target room temperature, especially on cold days. The installer should set the weather compensation curve during commissioning. If you adjust it yourself, monitor room temperatures for a few days and revert if the home feels cold.
MCS certification and TrustMark registration are the only reliable ways to verify a heat pump installer in the UK
All heat pump installers must be MCS-certified for BUS grant eligibility and to comply with building regulations (Part L 2021) (MCS, 2026). TrustMark is the government-endorsed quality scheme; all MCS installers should also be TrustMark-registered (TrustMark, 2026).
The installer should provide a full system design including flow temperature, heat loss calculation, and emitter sizing before installation. Check the MCS Installer Database online for a current certificate. Ask for a written quote that specifies the design flow temperature, and verify it matches your home’s heat loss and radiator sizes. How to choose a heat pump installer in the UK
Frequently Asked Questions
The ideal flow temperature is typically 45–50°C, not the default 55°C. Lowering to 45°C can improve your CoP from about 2.8 to 4.0, cutting electricity use by 30%. The Energy Saving Trust recommends adjusting based on your home’s heat loss.
Lower flow temperature directly cuts running costs. For every 1°C reduction, CoP improves by 2–3%, saving roughly £200–£350 per year for a typical 3-bed semi. Ofgem RHI data confirms CoP of 2.8–3.2 at 55°C vs 4.0 at 45°C.
Yes, but it must be done safely to avoid insufficient heating. Check your MCS installation manual and consult your installer. A drop from 55°C to 45°C is common, but ensure radiators or underfloor heating can still meet your home’s heat demand.
The default is 55°C, a legacy from gas boiler systems. However, DESNZ Electrification of Heat data shows average UK installations run at 50–55°C. Lowering to 45–50°C is recommended for better efficiency without compromising comfort.
Savings of £200–£350 per year for a 3-bed semi-detached home are typical. This is based on reducing flow from 55°C to 45°C, improving CoP from 2.8 to 4.0. Exact savings depend on your electricity tariff and home heat loss.
