Smarter Heating & Hot Water
Start from the gas and electricity on the bill. Tick what the home has, and the year is split into heating, hot water, and the rest. To go the other way, from boiler power and hours, use the boiler usage cost calculator.
Defaults are the Ofgem medium typical use: 9,500 kWh of gas and 2,500 kWh of electricity.
Last updated 1 October 2026. Ofgem Direct Debit average.
Off-peak is the advertised 8p/kWh from 1 October 2026. The day rate is an example and changes by region. Set the off-peak share on each appliance. A heat pump runs longer than a battery charge, so the rest is the day rate.
Panels yield about 900 kWh a year per kW. About 35% is used in the home, or about 70% with a battery. On a day and night tariff the battery shifts one charge a night, at 90% round trip. A heat pump runs on about 180 heating days, so a charge only covers part of that day and the rest is the day rate.
On a day and night tariff, set the share of each ticked use that can run off-peak. The car starts at 100%. A heat pump is not given a share: it runs through the day, the battery covers one charge, then it uses the day rate.
Estimate only. Gas is shared in typical proportions across the uses you tick. Each electric appliance takes a typical yearly amount, and what is left is other use. On a day and night tariff, the off-peak share of each ticked use is priced at the cheap rate. A battery moves one charge a night onto that rate, at 90% round trip. A heat pump runs on about 180 heating days. The battery covers one charge on those days, then the heat pump uses the day rate. Unused summer charge does not carry into winter. Solar is about 900 kWh a year per kW, with about 35% used in the home, or about 70% with a battery. Exported solar is not paid here. The electricity figure is what the home uses; solar covers some of it so less is imported. Heating hours assume 20 kW, hot water hours assume 36 kW, the same powers as the boiler usage cost calculator.