Load compensation controls

Load compensation adjusts the heating-water target using feedback from inside the building. Instead of firing at one fixed temperature until a thermostat switches off, a compatible controller can reduce or increase flow temperature according to how far the room is from target and, in some systems, how quickly it is changing.

The aim is to match heat delivery to the building’s current need. That can help a heat pump run steadily at a lower flow temperature, but only when the sensor, hydraulics and control influence are suitable.

How it differs from weather compensation

Weather compensation uses outdoor temperature to anticipate how the building heat loss changes. Load compensation uses indoor temperature to see the result.

The two approaches answer different questions:

• Weather compensation: what flow temperature is likely to be needed in these outdoor conditions?
• Load compensation: does the measured indoor temperature show that more or less heat is needed?

They can operate separately. They can also be combined, with an indoor sensor making a limited adjustment to a weather-derived target. Energy Saving Trust describes that combination as weather compensation with room influence.

Product names are inconsistent. “Load compensation”, “room influence”, “adaptive control” and “modulating room control” can describe different algorithms. Confirm from the controller instructions whether a setting shifts the heating curve, changes a target flow temperature, modulates output or simply turns demand on and off.

The indoor sensor represents the whole system

A sensor with strong control influence should be in a room that reasonably represents the heated building. Poor locations include:

• direct sunlight
• near a stove, cooker or other heat source
• behind furniture or curtains
• beside an outside door or draught
• in an unusually warm or cold zone
• on a wall heated by concealed pipework

A wireless sensor also needs reliable communication. A stale value can look plausible while the controller is acting on old data.

If a thermostatic radiator valve is fitted in the reference room, it can close the emitter before the main sensor reaches target. The two controls then fight. The design should define which control has authority and preserve adequate emitter flow.

Room influence must be proportionate

The controller may apply more heat when the room is below target and trim the flow as it approaches target. If the influence is too weak, indoor gains and unusual weather may take a long time to correct. If it is too strong, the target can jump up and down, causing overshoot, cycling or unwanted supplementary heat.

There is no universal correct influence value. Controller scales are manufacturer-specific, and building thermal mass changes the response. A heavy masonry or screeded floor system can continue releasing heat after the control has reacted. A lightweight building may respond more quickly.

Start from the commissioned value. Change one setting at a time and allow the building enough time to respond before judging it.

Compensation is not a substitute for design

Load compensation cannot repair:

• an undersized radiator or underfloor circuit
• insufficient primary flow
• poor hydraulic balancing
• excessive building heat loss
• a heat pump with inadequate capacity
• a domestic hot-water valve passing into the heating circuit

If one room is persistently cold while the reference room is comfortable, raising the whole system target may overheat the rest of the property. Check room heat loss, emitter output and water flow first.

The maximum flow-temperature limit remains a design safeguard. Increasing it so that compensation can recover faster can reduce efficiency or exceed the emitter design basis.

Zoning and minimum flow

Room controls can close valves or stop zone pumps while the heat pump still needs water flow and active system volume. The design must maintain the manufacturer’s minimum requirements in every possible operating state, including defrost.

Many small zones can turn a modulating heat pump into an on/off system. As each zone closes, the remaining heat demand may fall below the unit’s minimum stable output. A bypass can preserve flow but may also return hot water directly and cause cycling. A buffer can provide separation but may introduce mixing and additional pump energy.

The right solution is a coordinated hydraulic and control design, not an automatic accessory.

Setpoints and schedules

Load compensation still needs an indoor target. A schedule can change that target for occupancy or sleep, but a deep setback may prompt a large flow-temperature correction during recovery.

Check whether the control has separate modes for:

• normal room target
• setback or economy target
• holiday or frost protection
• temporary override
• domestic hot water

A temporary comfort change should not overwrite the installer-designed heating curve or maximum limits. The owner needs to know when an override expires.

Commissioning the control

Commissioning should confirm the sensor reading, configured control mode and response to a controlled change in room target. Record:

• sensor location and displayed temperature
• weather curve, if combined control is used
• room-influence or compensation value
• normal and setback targets
• zone valves, pumps and reference-room arrangement
• minimum flow and active volume in closed-zone states
• maximum flow and backup-heater limits

As at 22 July 2026, MIS 3005-I:2025 requires heat-pump commissioning to follow a documented procedure and the manufacturer’s instructions. Where weather compensation optimises efficiency, the standard says it should be enabled. Load compensation must therefore be configured as part of the declared control philosophy, not added in a way that defeats the weather-led design.

Diagnosing poor behaviour

The room overshoots

Check indoor sensor location, room influence, emitter output after demand falls, solar gains and whether the system is starting from a deep setback. Overshoot does not always mean the weather curve is too high.

The heat pump cycles around target

Review minimum compressor output, open emitter area, system volume, valve closure and control deadband. A very strong room correction can contribute, but hydraulic restrictions may be the main cause.

Other rooms remain cold

Check balancing, individual emitter output and zoning. The reference room may satisfy the controller before a slower room receives enough heat.

The controller keeps demanding high flow

Confirm the actual room value and target, schedule state, online sensor status and any temporary boost. Look for a sensor that is consistently reading low before changing installer settings.

Monitoring a change

Record the old and new setting, outdoor conditions, indoor temperature, flow target, actual flow and run pattern. Compare several representative periods rather than one hour.

Useful results are stable comfort, a sensible flow target and fewer unnecessary starts. A lower electricity total during milder weather is not proof by itself because the building load also fell.

Related entries

• Weather compensation controls
• Heat pump scheduling and setback
• Commissioning flow rates
• Buffer tank
• Handover settings and user controls