How to load-shift with a heat pump: cut your electricity bill by £200–£400 a year
Time-of-use tariffs offer rates as low as 14–17p/kWh during off-peak windows — roughly half the standard cap rate of 24.7p. But you only capture those savings if your heat pump actually runs during the cheap hours. Load-shifting moves your heating and hot water consumption into those windows. Done well, it's worth £200–£400 a year on the right tariff. This guide explains how to do it, what controls you need, and what’s realistic without it becoming a hobby.
The basic idea
A heat pump running at 14p/kWh costs roughly half as much to operate as the same pump running at 24.7p/kWh — the April 2026 standard price cap rate. The difference between those two rates is the entire financial case for time-of-use tariffs.
Load-shifting means scheduling your heating and hot water to happen during cheap windows, and avoiding — or at least reducing — consumption during expensive ones. Your home and your hot water cylinder act as thermal stores: you put heat in when electricity is cheap, and you live off that stored heat when it isn't.
It sounds technical. In practice, most of it is a one-time setup in your heat pump controller or thermostat.
What you can actually shift
Hot water
This is the easiest and highest-value load to shift. A typical household heat pump cylinder holds 180–250 litres and takes 60–90 minutes to reheat. If you schedule that reheat to happen entirely within a cheap-rate window, you capture the full rate discount on 1,000–1,500 kWh of annual hot water demand.
Most heat pump controllers let you set a hot water schedule separately from space heating. Set it to run once or twice in your tariff's cheap windows and leave it there.
One caveat: heat pump cylinders heat more slowly than immersion heaters (a 10 kW heat pump input takes around 75 minutes to recover a 250-litre cylinder from cold). Make sure the cheap window is long enough for a full reheat — a three-hour window is ample, a 30-minute window is not.
Space heating: preheat and setback
You can't stop your home losing heat, but you can time when the heat pump tops it up. The approach is:
- Preheat during cheap windows: run the heat pump slightly above your normal target temperature, so the building has a thermal buffer going into the expensive period.
- Setback during peak hours: allow the indoor temperature to drift down slowly while electricity is expensive. In a well-insulated home, this drift might be less than 1°C over the three-hour peak.
This works best in homes with good insulation and high thermal mass — solid walls, concrete floors, or underfloor heating. In a draughty property the benefit shrinks.
Weather compensation helps here too: a heat pump running weather compensation adjusts its output to the outdoor temperature automatically, which naturally concentrates more run-time in milder daytime hours and reduces the need for heavy-handed manual scheduling.
Appliances
Dishwashers, washing machines, and tumble dryers are worth shifting to cheap windows, but their contribution to heat pump electricity bills is small. At 6,000–8,000 kWh/year for heating and hot water versus 500–1,000 kWh for white goods, appliance scheduling is a nice bonus rather than the main event.
Which tariffs reward load-shifting
| Tariff | Cheap windows | Off-peak rate (Apr 2026) | Peak risk |
|---|---|---|---|
| Cosy Octopus | 04:00–07:00, 13:00–16:00, 22:00–00:00 | ~14.5p/kWh | Yes — 51p during 16:00–19:00 |
| EDF FreePhase | 23:00–06:00 (green), 06:00–16:00 & 19:00–23:00 (amber) | Green ~10–12p/kWh | Mild — 3 hrs at red rate |
| British Gas Heat Power | 00:00–07:00, 13:00–16:00 | ~12p/kWh | No explicit peak |
| E.ON Next Pumped | 22:00–06:00 | ~9–11p/kWh | No explicit peak |
| Octopus Agile | 48 half-hourly slots, varies | Avg ~22p, dips to 5–10p | Yes — spikes possible |
Cosy Octopus has the most cheap hours (8 hours/day) but also the highest peak rate — 51p/kWh during 16:00–19:00 under the April 2026 price cap. If you can avoid that window, the savings are substantial. If you can't, a tariff without a peak rate like E.ON Next Pumped may serve you better.
You can run your own numbers for each tariff against your actual half-hourly usage on Octopus via Heat Pump Tariffs.
How much can you save?
Based on a typical three-bedroom home with a 6 kW heat pump, 6,600 kWh annual electricity demand, and 70% of heating and hot water shifted to cheap windows:
| Scenario | Estimated annual saving vs standard cap |
|---|---|
| Passive user (no load-shifting) | ~£35 |
| Active scheduler (70% shifted) | £200–£400 |
| Optimal scheduler + avoiding peak | £350–£500 |
The gap between a passive and active user on the same tariff is significant. Choosing a time-of-use tariff but not changing when your heat pump runs means paying a peak rate for no reward.
What controls do you need?
At minimum: a heat pump controller or thermostat that supports time-of-day scheduling. Most modern heat pumps (Vaillant, Daikin, Mitsubishi, Samsung, Nibe) include this in their app or wired controller.
For more flexibility: a smart thermostat (Hive, tado°, Honeywell Home) or home automation platform (Home Assistant, Homely) lets you align schedules precisely to your tariff windows and adjust them when tariff rates change.
For full automation: integrations like Home Assistant with the Octopus Energy integration can read live tariff rates and trigger your heat pump and hot water boost automatically during the cheapest slots — without you touching anything.
You don't need any of this to start. Setting a fixed hot water schedule in your heat pump app to match your tariff's cheap windows is a five-minute job and captures most of the saving.
Common mistakes
Running the peak rate unnoticed. If you're on Cosy Octopus, check whether your heat pump or immersion heater is running between 16:00 and 19:00. A single immersion heater left on boost during peak hours can wipe out most of the off-peak savings.
Cylinder too small to buffer overnight. If your cylinder runs out before the morning cheap window starts again, the heat pump tops up at the standard or peak rate. A 200–250 litre cylinder is the sweet spot for most households; smaller cylinders may need a midday top-up schedule.
Expecting exact savings. The £200–£400 figures are modelled averages. Your actual saving depends on your home's heat loss, how well you shift load, and which DNO region sets your tariff rates. Running your own comparison against real usage data is the only way to know what's achievable for your home.
The short version
- Identify your tariff's cheap windows.
- Set your hot water schedule to heat within those windows.
- Enable a preheat before, and setback during, any peak period.
- Check that nothing energy-hungry (immersion boost, washing machine) is running at peak.
- Review your Bright or smart meter data after a month to see whether consumption shifted.
That's it. The hardware is probably already there. The scheduling takes 10 minutes. The saving accumulates for as long as you stay on the tariff.
Compare what load-shifting is actually worth for your home on Heat Pump Tariffs — using your real half-hourly data, not national averages.