Model storage-heater charging at an off-peak rate and daytime boost at a separate peak rate across your heating season.
Dual-rate tariffs · Economy 7/10 · Seasonal total
Use the night or off-peak unit rate from your own tariff.
Overnight energy is heater rating × off-peak charge hours × input level × heater count. Daytime boost is calculated separately at the peak tariff, then both are multiplied by used days in the heating season.
The rating plate, automatic charge control, retained heat, room losses and tariff clock determine actual use. A price-cap single-rate average is not an off-peak quote.
A generic wattage calculator misses the core storage-heater decision: most energy should be bought in the off-peak window, while boost can be charged at a higher daytime rate.
Enter the rates shown on your bill. Ofgem notes that Economy 7 windows and available rates vary by location and supplier.
Input or charge level controls how much energy is stored overnight. Lower it in milder weather or when the room will be unused.
Peak boost can prevent a cold evening but is usually the costly part. The separate boost output shows how repeated small top-ups accumulate over a season.
Multiply its charge rating by the off-peak hours and input level, then by your night rate. This calculator also adds any daytime boost at the more expensive peak rate and scales across your heating season.
Use the tariff and meter arrangement you actually have. Economy 7 normally offers seven cheaper hours; other multi-rate tariffs may provide longer or split windows. Compare both rates and total household usage, not only the heater rate.
On traditional storage heaters the output control releases heat already stored, so turning it up does not itself buy more energy. It may exhaust stored heat sooner and lead to peak-rate boost use later.
Boost or a built-in convector can use electricity when you need it, often at the peak tariff. Separating that use prevents a misleading single-rate estimate.
