The Little Heater That Ate the Winter Budget
Tom moved into a converted top-floor flat last autumn. It had big sash windows, a lovely view of the rooftops, and storage heaters that the letting agent described, generously, as “characterful”. By the first cold week he’d given up on them and bought a small fan heater from the supermarket for £25.
It was brilliant. It sat under his desk, warmed his feet in minutes, and he barely thought about it. He worked from home, so it ran most afternoons and evenings.
Then his first quarterly bill arrived, and it was nearly double the one before.
A small box with a big appetite
The heater was small, but its label said 2000W — two kilowatts. That’s a typical rating for a plug-in fan heater, and not far off a kettle. The difference is that a kettle runs for three minutes; Tom’s heater was running for five hours a day.
Electricity is billed in kilowatt-hours (kWh): a 2kW appliance running for one hour uses 2kWh. So five hours a day is 10kWh, every day, from one appliance.
Tom put his heater into the electric heater cost calculator with the unit rate from his bill. We’ve used an illustrative £0.27 per kWh here — check your own bill, because rates vary by supplier and change over time.
| Heater | Use | Cost per week | If run like this all year |
|---|---|---|---|
| 2kW fan heater | 5 hours a day, 7 days | £18.90 | £982.80 |
| 1kW setting | 5 hours a day, 7 days | £9.45 | £491.40 |
Nobody heats all year, of course. But over a twenty-week cold season, that 2kW heater would cost around £378. For a £25 purchase, that’s quite a running cost.
The label isn’t the whole story
Here’s where Tom’s story gets more interesting. He borrowed a plug-in energy monitor from a friend (they’re inexpensive, and some libraries lend them) and plugged the heater into it for a week.
The monitor showed 43kWh over seven days — well under the 70kWh the label suggested. The reason is the thermostat. Once his feet were warm and the room had caught up, the heater clicked off for minutes at a time, then on again. The rated 2000W is what it draws when it’s heating; the average is lower.
The kWh cost calculator turns that measured figure straight into money: 43kWh at £0.27 is £11.61 for the week. Still a big chunk of his bill, but a long way from the worst case.
That’s the honest picture for most heaters, fridges and dehumidifiers: the label gives you the maximum, the meter gives you the truth. If you can’t measure, the label-based figure is a useful upper limit — just don’t be surprised when reality comes in a little lower.
What Tom changed
Armed with real numbers, Tom made three small changes rather than one big sacrifice:
- Lower setting, longer warm-up. Most fan heaters have a 1kW setting. On a mild day, that halves the power when the heater is running.
- Heat the person, not the flat. He closed the door to the room he worked in, added a draught excluder at the bottom, and stopped trying to warm the whole open-plan space.
- Timer instead of “on”. A cheap plug-in timer stopped the heater running into the night when he’d forgotten about it.
Within a month his measured use was down to about 25kWh a week. The heater stayed — it just stopped being invisible.
Run your own numbers
If you have a plug-in heater, an oil-filled radiator or anything else with a wattage on the label, it takes about a minute to check:
- Find the wattage on the label (W, or kW × 1000).
- Estimate the hours a day you really use it.
- Use your own unit rate from your bill — Ofgem publishes the current price cap rates if you’re on a standard variable tariff.
The watts to kWh calculator is handy for the in-between step, and the appliance running-cost calculator works the same way for anything else in the house — a dehumidifier, a tumble dryer, a second fridge in the garage.
Tom’s verdict? “It was never the heater’s fault. I just didn’t know what it was doing.”