Heat pump scheduling and setback

How to schedule heat-pump space heating, choose a setback and assess recovery without relying on generic settings.

Heat pumps often work well with long, steady heating periods because low-temperature emitters deliver heat gradually. That does not make every setback wrong. Lowering the indoor target can reduce building heat loss while the space is cooler, but recovery may require more heat at a less favourable time or temperature.

The right schedule depends on the building, emitters, heat pump, tariff and occupants. A generic instruction to run continuously or turn down by a fixed number of degrees can be wrong for both comfort and energy use.

What a setback changes

During a setback, the room target is reduced or heating is suspended. The building cools according to its insulation, air leakage, thermal mass, outdoor conditions and internal gains.

When the normal target returns, the system must provide the current heat loss plus enough additional heat to restore the building temperature. The recovery can expose constraints that are hidden during steady operation:

insufficient emitter output at the normal weather-compensated flow
heat-pump capacity already committed to the building load
a controller that raises flow temperature aggressively
supplementary electric heat enabled during a large temperature error
domestic hot-water priority interrupting recovery
several zones calling at once

A low-temperature system may recover slowly by design. Slow is not automatically inefficient, but it must still meet the agreed occupancy pattern.

Continuous operation is not literally constant output

Leaving heating enabled does not mean the compressor runs at full power all day. A modulating heat pump can reduce output, and weather compensation can lower the water target as outdoor conditions become milder.

Room controls may also stop demand once the building is warm. The useful comparison is between complete control strategies, not “on” versus “off” as if heat delivery were fixed.

Continuous availability often suits buildings with high thermal mass, underfloor heating or emitters sized close to the design duty. A more pronounced schedule can suit a responsive building that is unoccupied for a meaningful period. Neither result should be assumed without considering recovery.

Start with comfort requirements

Define when each occupied area needs to be at its target, including mornings, home working, shift patterns and vulnerable occupants. Then work backwards from measured recovery behaviour.

The heating start time is not necessarily the desired warm time. Some controls calculate an optimum start; others change target at a fixed clock time. Confirm which behaviour is active.

Avoid stacking independent schedules in an app, room thermostat, heat-pump controller and zone controls. One device may cancel demand while another believes heating is available.

Weather compensation during recovery

A well-tuned weather curve provides the flow temperature needed to maintain comfort for the prevailing outdoor condition. Recovery creates an additional temporary load.

Controllers respond in different ways. Some retain the weather-derived target and recover gradually. Others add room influence or a boost. An excessive boost can make the heat pump work at a higher temperature, close thermostatic valves as rooms catch up and trigger cycling.

Do not raise the installer maximum flow temperature just to make one morning recovery faster. First consider a smaller setback, earlier start, better emitter output or a more suitable room-influence value.

Tariffs do not remove the heat balance

A time-of-use tariff can make it attractive to shift some heating into a lower-price period. Preheating stores energy in the building fabric or a thermal store, but it also raises indoor temperature and therefore building heat loss during that period.

The result depends on:

the difference between tariff periods
heat-pump COP in each outdoor and flow-temperature condition
how much useful heat the building can retain
comfort limits
battery losses if stored electricity is involved
whether a high flow target or immersion is triggered

Tariff modelling uses the dated rates offered to the household. A cheap unit of electricity is not a saving if much more electricity is consumed to force rapid preheating.

Domestic hot water needs its own schedule

Cylinder reheating normally uses a higher flow temperature and may pause space heating. Coordinate it with the heating schedule so a long hot-water call does not occupy the intended room-recovery period.

Keep the bacterial-growth control separate. A pasteurisation cycle must complete the outcome required by the system risk assessment. It should not be shortened or disabled to fit a price window.

Holiday and frost modes

Holiday mode may reduce room targets, suspend hot-water schedules or apply frost protection. Product behaviour varies. Check:

which parts of the building remain protected
exposed monobloc water pipework and freeze-protection method
whether circulation pumps need power
domestic hot-water hygiene on return
how and when normal operation resumes

Turning off electrical supply can disable frost protection, pumps, trace heating and remote alarms. Follow the manufacturer and system handover instructions.

A practical tuning method

Begin with the commissioned weather curve and a schedule that meets comfort. Choose one representative area and record:

normal and setback targets
setback start and recovery start
outdoor and indoor temperatures
target and actual flow temperatures
compressor and supplementary-heater operation
domestic hot-water periods
electricity and delivered heat over a consistent boundary

Make one modest change, such as adjusting the recovery start or reducing the depth of setback. Observe it across comparable conditions before changing anything else.

Weather varies, so raw daily electricity is a poor comparison. Use indoor temperature, degree of recovery, flow temperature and run pattern alongside energy. A single warm day can make any schedule look efficient.

Common failure patterns

The home is cold each morning

The setback may be too deep or recovery too late. Also check whether hot-water priority, zoning or an undersized emitter is limiting output. Raising the weather curve everywhere can overheat the house later.

Supplementary heat runs during recovery

Check the controller’s backup enable condition, room-temperature error, maximum compressor duty and outdoor lockout. The heat pump may be correctly sized for steady design load but the schedule is demanding an avoidable recovery peak.

Electricity use rises after shifting to a cheap period

Review the total heat delivered, flow temperature, outdoor condition, preheat target and battery path. More heat, poorer COP or storage losses can outweigh the tariff difference.

The heat pump starts and stops repeatedly overnight

The setback target may sit close to room temperature, the active zone may be too small or the unit’s minimum output may exceed the load. Inspect hydraulic state and control deadband rather than simply widening the schedule.

Keep settings recoverable

Record the working schedule, curve, room influence, backup limits and hot-water periods at handover. Save screenshots or an installer report where the controller has no export function.

After a firmware update, app migration or service visit, compare the active settings with that record. A reset schedule can change performance without any mechanical fault.