| Ofenwerk K1 | Oil-filled radiator | |
|---|---|---|
| Warm-up | About 2 seconds | 20–30 minutes |
| Typical power | 1200W | 1500–2500W |
| Weight | 0.5 kg | 8–15 kg |
| Best for | Quick, targeted warmth | Background heat left on all day |
| Tip-over cut-off | Yes | Some models |
Which is cheaper to run?
Per kWh, both cost exactly the same. Electric heating is about 100% efficient whatever the type. The real difference is how long each one has to run. An oil radiator spends its first half-hour heating oil before you feel much warmth, while the K1 gives warm air almost straight away. If you only need heat for an hour or two, the K1 usually costs less.
When an oil radiator makes sense
If you want a silent heater left on low all day in a large room, an oil-filled radiator is a good choice. For bedrooms, home offices and evenings on the sofa, the K1 is quicker, lighter and easier to move.
See also: K1 vs a standard fan heater · running cost calculator.
What it costs to run (current UK prices)
At the Ofgem price cap of 26.32p per kWh (1 October to 31 December 2026), a 1200W heater like the K1 costs about 32p an hour at full power. Once the room is warm the thermostat switches the heater on and off, so in normal use it averages about 16p an hour.
| How long | Typical cost per day | Over 30 days |
|---|---|---|
| 1 hour | 16p | £4.74 |
| An evening (4 hours) | 63p | £18.95 |
| A working day (8 hours) | £1.26 | £37.90 |
Your own price may be a little higher or lower depending on your region and tariff. See how we calculate running costs or try the running cost calculator with your own unit rate.
How the K1 compares with other heaters
| Heater type | Warm in | Running cost | Safety and comfort |
|---|---|---|---|
| Ofenwerk K1 (ceramic) | About 2 seconds | About 16p/hour typical | Tip-over and overheat cut-off, cool-touch case, no glowing coil |
| Coil fan heater (2–3kW) | Seconds | 53–79p/hour at full power | Hot coil, can smell of burnt dust, often noisy |
| Oil-filled radiator (1.5–2.5kW) | 20–30 minutes | 39–66p/hour at full power | Surfaces get hot, heavy to move |
| Convector (2kW) | 10–15 minutes | About 53p/hour at full power | Heat rises to the ceiling first |
| Electric blanket (100W) | 10–20 minutes | About 3p/hour | Warms the bed only, not the room |
Full-power costs worked out at 26.32p per kWh. Thermostats lower all of these in real use.
Using any electric heater safely
These tips follow UK fire-service and Electrical Safety First advice and apply to any portable heater, including ours:
- Plug the heater straight into a wall socket. Don't use an extension lead or adaptor; they can overheat.
- Keep it at least 1 metre from curtains, bedding, clothes and furniture.
- Stand it on a flat, hard, stable surface where it can't be knocked over.
- Never cover it or dry clothes on it.
- Switch it off at the wall when you go out.
- Check the plug and cable now and then. Stop using it if either is damaged or feels hot.
- Make sure you have a working smoke alarm on every floor. Many UK fire services fit them free for older residents.
When the K1 is not the right choice
We'd rather you buy the right heater than return ours. The K1 is probably not for you if:
- You want to heat a large open-plan space over about 20 m² with one heater.
- You want to replace central heating for the whole house.
- You need total silence. The K1 has a gentle fan sound.
Sources and how we checked this guide
- Electricity price: Ofgem: energy price cap unit rates and standing charges, checked 25 October 2026.
- Heater safety: UK fire and rescue service advice and Electrical Safety First guidance on portable heaters.
- K1 figures (1200W, about 2-second warm-up, room size up to 20 m², safety cut-offs) come from the product specification.
- Costs are worked out with the method on how we calculate running costs.