Live Direct Debit rates for UK average since 1 October 2026. Night price example: Octopus Economy 7, London, from 1 October 2026.
The short answer
A storage heater fills up with heat overnight, when Economy 7 electricity is cheaper, and gives it out during the day. Night rates are usually less than half the day rate.
For example, on Octopus Energy's standard Economy 7 tariff in London from 1 October 2026, night electricity costs 13.99p per kWh and day electricity 33.11p. Rates vary by region and supplier, so check your bill.
| Heater size | Night charge (7 hours) | Cost at 13.99p (night) | Same energy at 33.11p (day) |
|---|---|---|---|
| 1.7 kW (small room) | 11.9 kWh | £1.66 | £3.94 |
| 2.55 kW (medium room) | 17.9 kWh | £2.50 | £5.91 |
| 3.4 kW (large room) | 23.8 kWh | £3.33 | £7.88 |
These are full overnight charges, used on the coldest days. On milder days you can turn the input down and pay less.
The two controls
- Input (charge): how much heat it stores overnight. Set it higher when tomorrow will be cold, lower when it will be mild.
- Output (boost or damper): how fast it releases heat. Keep it low in the morning so heat lasts into the evening.
How to avoid big bills
- Avoid the "boost" button. On many heaters it uses day-rate electricity, which costs over twice as much.
- Check the weather forecast and set the input the night before.
- Check your Economy 7 hours. They differ by meter. They're usually 7 hours between about 10pm and 8am, and may follow GMT all year.
- Run other appliances at night too, like the washing machine or dishwasher on a timer, to use the cheap rate.
Old storage heaters can leak heat all day. Modern high heat retention models hold it much better, and may be worth upgrading to. Compare with plug-in electric heaters.
Sources: Octopus Energy Economy 7 rates, Octopus Energy tariff data.