Weather compensation and controls for UK heat pumps
Weather compensation transforms how heat pumps operate in UK homes, adjusting output temperatures based on outdoor conditions rather than running at fixed settings.
This approach cuts energy consumption by 10-25% compared to constant-temperature operation, yet fewer than half of UK heat pump installations use it properly.
Understanding how weather compensation works—and how to configure it for British weather patterns—makes the difference between a system that merely functions and one that delivers genuine efficiency gains.
The principle is straightforward: when it's 12°C outside, your home needs less heating than when it's -3°C.
Weather compensation curves automatically reduce flow temperatures as outdoor temperatures rise, maintaining comfort whilst minimising electricity use.
For UK households paying 24-28p per kWh, this matters considerably.
How weather compensation works in practice
A weather compensation curve plots the relationship between outdoor temperature and the flow temperature your heat pump produces.
When outdoor temperature drops, flow temperature increases.
When it's milder, flow temperature decreases.
The curve's gradient determines how aggressively the system responds to weather changes.
Most UK heat pumps use a sensor mounted on a north-facing external wall, away from direct sunlight, vents, and windows.
This sensor feeds real-time outdoor temperature data to the heat pump controller, which adjusts flow temperature according to the programmed curve.
The adjustment happens continuously—not in sudden jumps—creating stable indoor conditions.
Typical UK weather compensation range: Flow temperatures between 25°C (outdoor temp 15°C) and 45°C (outdoor temp -3°C) for well-insulated homes with underfloor heating.
The curve you need depends entirely on your property's heat loss characteristics and emitter type.
A 1930s semi with cast iron radiators requires steeper curves and higher flow temperatures than a 2010-built house with underfloor heating.
This is why installer competence matters—generic curves rarely deliver optimal results.
Setting up weather compensation curves for UK conditions
Configuring weather compensation requires three key parameters: the base point (flow temperature at a reference outdoor temperature, typically 20°C), the design point (flow temperature at your design outdoor temperature, usually -3°C for most of England), and the curve gradient connecting them.
Start with conservative settings, then refine based on actual performance.
If rooms feel cold during mild weather, your curve may be too shallow.
If the house overheats when outdoor temperatures rise, the curve is too steep.
Adjustments of 2-3°C in flow temperature often produce noticeable comfort changes.
| Property type | Emitter system | Typical curve gradient | Flow temp at -3°C | Flow temp at 15°C |
|---|---|---|---|---|
| Modern (post-2006) | Underfloor heating | 0.8-1.2 | 35-40°C | 25-28°C |
| Modern (post-2006) | Oversized radiators | 1.2-1.5 | 40-45°C | 28-32°C |
| Older (pre-1990) | Standard radiators | 1.5-2.0 | 45-50°C | 32-38°C |
| Older (pre-1990) | Upgraded radiators | 1.3-1.7 | 42-47°C | 30-35°C |
These figures represent starting points, not fixed rules.
A draughty Victorian terrace with original sash windows needs different settings than an identical property with secondary glazing and loft insulation.
Monitor actual indoor temperatures over several weeks, particularly during transitional weather in October and March when outdoor temperatures fluctuate significantly.
Pro Tip: Run your heat pump for at least two weeks before adjusting weather compensation curves.
Initial settings often feel wrong because the building fabric is still warming up or cooling down from previous heating patterns.
Thermal mass in floors and walls takes time to stabilise, particularly in solid-wall properties.
Room thermostats versus weather compensation
This causes considerable confusion.
Weather compensation adjusts flow temperature based on outdoor conditions.
Room thermostats measure indoor temperature and switch the system on or off.
Using both simultaneously creates conflicts unless configured correctly.
The most effective approach for UK heat pump installations: use weather compensation as the primary control, with room thermostats set 1-2°C above desired temperature as a safety limit.
This allows weather compensation to modulate output continuously whilst preventing overheating if the curve is set too aggressively.
"We see many installations where room thermostats are set to 21°C and weather compensation is enabled, but the two systems fight each other.
The thermostat cuts power just as the heat pump reaches optimal efficiency.
Set the thermostat to 23°C as a ceiling, let weather compensation do the work, and adjust the curve if rooms feel cold."
Some installers disable weather compensation entirely, relying solely on room thermostats.
This approach works but sacrifices 15-20% efficiency because the heat pump runs at fixed flow temperatures regardless of actual heating demand.
On a mild February day requiring minimal heating, the system still produces 45°C flow temperatures when 35°C would suffice.
Efficiency impact: Heat pumps achieve COP (Coefficient of Performance) of 4.2 at 35°C flow temperature versus 3.2 at 45°C in typical UK conditions.
That's 30% more electricity for the same heat output.
Advanced control strategies for UK weather patterns
Basic weather compensation responds only to outdoor temperature.
More sophisticated approaches incorporate additional factors relevant to British weather: wind speed, solar gain, and rate of temperature change.
Wind compensation adjusts flow temperatures upward during windy conditions because wind increases heat loss through building fabric.
A house at 8°C outdoor temperature with 25mph winds loses heat faster than the same house at 8°C with calm conditions.
Some Vaillant and Daikin models include wind compensation, though it requires an anemometer installation.
Solar compensation reduces flow temperatures when sunshine warms the building.
This matters particularly for south-facing properties with large windows.
Without solar compensation, weather compensation curves based purely on outdoor temperature can overheat rooms on sunny winter days.
The system sees 6°C outside and delivers high flow temperatures, ignoring the 2-3°C temperature rise from solar gain.
Adaptive weather compensation learns from actual indoor temperature responses, automatically adjusting curves over time.
If rooms consistently run 0.5°C warmer than the setpoint during specific outdoor conditions, the system reduces flow temperatures for those conditions.
This self-optimisation suits UK weather variability, where outdoor temperatures can swing 10°C within 24 hours.
Zoning and individual room control
Weather compensation works at system level, setting one flow temperature for the entire heating circuit.
This creates challenges in UK homes where room heating requirements vary significantly—a north-facing bedroom needs more heat than a south-facing living room with a wood burner.
Zoning divides the heating system into separate circuits, each with its own weather compensation curve.
A typical setup: ground floor (living areas with high solar gain and supplementary heating) on one zone with a shallow curve, first floor (bedrooms with lower target temperatures) on another zone with a steeper curve.
Individual room control using thermostatic radiator valves (TRVs) or underfloor heating zone valves provides finer adjustment.
However, closing too many zones simultaneously reduces flow through the heat pump, potentially causing short cycling and efficiency losses.
Aim to keep at least 40-50% of emitters open at any time.
Pro Tip: If using TRVs with weather compensation, fit them to radiators in rooms with variable heating needs (spare bedrooms, home offices used intermittently) but leave main living areas without TRVs.
This maintains adequate flow through the system whilst allowing targeted temperature reduction in specific rooms.
Setback and scheduling with weather compensation
Traditional gas boiler advice—turn heating off overnight or when out—doesn't translate directly to heat pump operation with weather compensation.
Heat pumps achieve best efficiency running continuously at low output rather than cycling on and off.
Night setback (reducing target temperature overnight) can work with weather compensation, but the temperature reduction should be modest: 2-3°C maximum, not the 5-7°C drops common with gas boilers.
The heat pump needs 2-3 hours to recover from deeper setbacks, often running at higher flow temperatures (lower efficiency) during the recovery period.
An alternative approach: maintain constant temperature 24/7, relying on weather compensation to minimise energy use during milder periods.
For a well-insulated UK home, the energy saving from night setback often amounts to 5-8% of heating costs—worthwhile but not transformative.
Weigh this against reduced comfort and potential efficiency losses during recovery periods.
Real-world data: Heat Pump Monitoring Programme data shows UK heat pumps with night setback averaging COP of 2.8 versus 3.1 for continuously-run systems with weather compensation.
The 10% efficiency gain often exceeds energy saved from setback.
If you do use setback, configure it through the weather compensation controller rather than room thermostats.
This allows the system to reduce flow temperatures proportionally rather than switching off entirely.
A 2°C setback might reduce flow temperature from 40°C to 36°C—the heat pump continues running efficiently at lower output.
Troubleshooting common weather compensation issues
Rooms feel cold during mild weather (10-15°C outdoor temperature): Your curve is too shallow or the base point is set too low.
Increase flow temperature at the mild-weather end of the curve by 2-3°C.
This is the most common issue in UK installations because installers often copy curves from continental European settings where homes have better insulation.
House overheats when outdoor temperature rises above 12°C: Curve is too steep or doesn't reduce flow temperature aggressively enough in mild conditions.
Lower the base point or reduce curve gradient.
Consider whether solar gain is contributing—south-facing rooms may need separate zoning.
System short-cycles (frequent on-off switching): Flow temperature may be too high for actual demand, causing rooms to reach temperature quickly.
Reduce curve gradient.
Alternatively, check whether too many TRVs are closed, restricting flow.
Short cycling damages compressor longevity and kills efficiency.
Inconsistent temperatures between rooms: Weather compensation sets one flow temperature for all emitters.
If some rooms are consistently warmer or colder, the issue is emitter sizing or heat loss variation, not weather compensation settings.
Address through zoning, TRVs, or emitter upgrades rather than curve adjustments.
High electricity consumption despite weather compensation: Check actual flow temperatures against programmed curve—some systems default to fixed-temperature operation if the outdoor sensor fails.
Verify the sensor is working and positioned correctly.
Also confirm the heat pump isn't oversized, as this causes cycling even with weather compensation.
Optimisation checklist for UK installations
- Verify outdoor sensor location: north-facing wall, 1.5-2m height, away from vents and windows
- Record baseline settings: note initial curve parameters before making changes
- Monitor for two weeks minimum before adjusting curves
- Make small adjustments: 2-3°C changes in flow temperature, wait 3-5 days to assess impact
- Check flow temperatures match programmed curve using heat pump display or app
- Set room thermostats 1-2°C above desired temperature as safety limit, not primary control
- Document final settings: record curve parameters, outdoor design temperature, and any zone-specific adjustments
- Review settings seasonally: curves optimised for January may need adjustment for October/March shoulder seasons
- Consider professional re-commissioning after first year if comfort or efficiency concerns persist
Smart controls and weather compensation integration
Modern heat pump controllers from manufacturers like Vaillant, Daikin, and Mitsubishi offer smartphone apps that display weather compensation curves graphically and allow remote adjustment.
This accessibility tempts frequent tinkering—resist the urge.
Effective weather compensation requires stability and observation over weeks, not daily tweaking.
Third-party smart controls (Nest, Hive, Tado) generally work poorly with weather compensation because they're designed for on-off boiler control.
They override weather compensation by switching the heat pump off when target temperature is reached, then back on when temperature drops.
This defeats the purpose of continuous modulation.
If you want smart features, choose systems designed for heat pumps: Vaillant sensoAPP, Daikin Madoka, or dedicated heat pump controllers like mixergy.
These integrate with weather compensation rather than fighting it, allowing remote monitoring and adjustment whilst maintaining efficient operation.
Regulatory and installer considerations
MCS (Microgeneration Certification Scheme) standards require installers to commission weather compensation on all heat pump installations unless there's a documented reason not to.
Despite this, many UK installations run without it or with poorly configured curves because installers lack training or time for proper commissioning.
When obtaining quotes, ask specifically how the installer will configure weather compensation.
Request details about curve calculation methodology, sensor positioning, and post-installation optimisation.
Installers who provide vague answers ("we'll set it to standard settings") often lack the expertise for proper commissioning.
Post-installation, you should receive documentation showing: the programmed weather compensation curve (graphically or as numerical parameters), outdoor design temperature used for calculations, expected flow temperatures at various outdoor conditions, and guidance for minor adjustments.
If this isn't provided, request it—you'll need this information for future optimisation.
Long-term performance and seasonal adjustment
Weather compensation curves optimised for January conditions may not suit October or April when heating demand is lower but still present.
Some households run two curves: a winter curve for November-March and a shoulder-season curve for October, April, and May with reduced flow temperatures.
Switching between curves manually works but requires attention.
More sophisticated controllers offer automatic seasonal adjustment, gradually shifting the curve as average outdoor temperatures change.
This suits UK weather patterns where spring and autumn can bring both 5°C mornings and 18°C afternoons within the same week.
Annual review of weather compensation settings makes sense, particularly after insulation upgrades or changes to the heating system.
Adding loft insulation or replacing windows reduces heat loss, allowing lower flow temperatures.
Update your curve to reflect these improvements—continuing to run at previous settings wastes the efficiency gains from retrofit work.
Weather compensation represents the single most effective control strategy for UK heat pump installations, yet it remains underutilised and poorly understood.
The efficiency gains—typically 15-20% compared to fixed-temperature operation—translate to £150-300 annual savings for average households.
More importantly, proper weather compensation delivers consistent comfort without the temperature swings common in poorly configured systems.
The initial effort to understand and optimise curves pays dividends throughout the heat pump's 15-20 year lifespan.