The short answer
At equal continuous electrical input, operating time and tariff, an oil-filled radiator and a fan heater have the same electricity cost. Different controls, cycling or required use time can change the total. Compare the heating task and actual energy rather than assuming the appliance shape creates a saving.
Equal electrical input has an equal electricity cost
If an oil-filled radiator and a fan heater each draw 1,500 W continuously for one hour, each uses 1.5 kWh. At an illustrative £0.28/kWh, each costs £0.42 for that hour.
That arithmetic does not depend on the shape of the appliance. A difference in total cost needs a difference in input, operating time, tariff or the task being performed.
Heat delivery and control can differ
Pro Breeze describes fan heaters as warming and cooling quickly, while oil-filled radiators warm more slowly and retain warmth after switching off. Its guidance also explains that thermostats can cut or reduce input once a set temperature is reached.
Retained warmth comes from energy supplied earlier. It should not be added as a separate electricity saving without measuring the complete heating task, including the warm-up period.
Comfort, control accuracy, placement and response time can matter to the routine you choose. Those considerations are different from a claim that equal sustained watts have different hourly electricity prices.
Do not confuse a lower rating with an equal heating task
| Illustrative input | Continuous use time | Energy | Cost at £0.28/kWh |
|---|---|---|---|
| 1,000 W | 2 hours | 2 kWh | £0.56 |
| 1,500 W | 2 hours | 3 kWh | £0.84 |
| 2,000 W | 2 hours | 4 kWh | £1.12 |
The lower-input example costs less over the same uninterrupted time. It does not establish that it achieves the same room temperature in the same conditions.
To compare actual routines, record the room, starting conditions, target setting and heating period. Compare accumulated electricity for a comparable result, rather than selecting an appliance simply because its maximum rating is smaller.
Use measured energy for a thermostat-controlled comparison
Consider an illustrative comparison of two five-day samples in otherwise comparable conditions. One heater uses 18 kWh and the other uses 20 kWh. At £0.28/kWh, those samples cost £5.04 and £5.60 respectively.
The difference is £0.56 over those five days. It is evidence about those samples, not a general saving for every oil-filled or fan heater. Differences in weather or room use could make even that comparison unsuitable.
Use measured mode in the heater calculator for each completed-day sample. Do not multiply the measured kWh by an additional assumed thermostat factor.
Separate appliance cost from whole-home heating
An appliance-only reading does not show how another heating system responds. If central heating changes at the same time, a room-heater saving alone is insufficient to establish a household saving.
Energy Saving Trust treats secondary electric heating as one part of a wider heating decision. Read the 1500 W worked example for tariff arithmetic and the measurement guide for recording useful samples.