Plugin portable unit
£6a night
Roughly 75p an hour, run for eight hours. £42 across a hot week.
Press estimate (uSwitch), widely quoted.
What it costs to run, in numbers we are happy to be checked on. No install prices here; those come as one figure, in writing, after a survey.
Search for the cost of cooling a bedroom and you will find seventy-five pence an hour, six pounds a night, forty-two pounds across a hot week. Those figures are real. They describe a portable plug-in unit, the kind with a hose out the window. They say nothing about a fixed system.
Roughly 75p an hour, run for eight hours. £42 across a hot week.
Press estimate (uSwitch), widely quoted.
What owners of a properly fitted system report running theirs for.
Self-reported by owners, Mumsnet.
Figures illustrative. Your fixed quote follows a survey.
Many of the people who talk to us have already bought the portable unit. It sits in a cupboard for eleven months, blocks a window for the twelfth, and never quite worked. This page is for what comes after that.
| Heat source | Cost per kWh of heat delivered |
|---|---|
| Gas boilerReal-world efficiency, around 85% | 8.6p |
| Fern systemTypical install, COP 3.0 to 3.5 | 7.5–8.7p |
| Electric heaterPanel, storage, oil-filled, any kind | 26.1p |
Ofgem price cap, July to September 2026. Electricity 26.11p per kWh, gas 7.33p. Boiler efficiency taken from field-study data, not the nameplate figure.
You will hear that oil-filled radiators are "more efficient" than other electric heaters. They are not, and the myth is worth killing. Every plug-in heater, oil-filled or otherwise, turns one unit of electricity into one unit of heat. That is the ceiling. A heat pump does not make heat from electricity at all. It moves warmth that is already outside, in the air, and for one unit of electricity it moves three or four units of heat indoors. That is the whole difference, and it is why the numbers above look the way they do.
Anywhere currently running on a panel heater is the clearest win in this whole page. A winter of resistive electric heat costs roughly £204. A heat pump doing the same job costs roughly £58 to £68.
Figures illustrative. Your fixed quote follows a survey.
Firing the whole boiler to warm the room you actually sit in, for one person, most of the day, is an odd trade. Heating the home office on its own typically costs roughly £130 to £150 a year run this way.
Figures illustrative. Your fixed quote follows a survey.
This is the part a comparison table cannot show. Gas has no column for July. When the loft room hits thirty degrees at ten at night, a boiler has nothing to offer. A Fern system runs in reverse and brings the room back down.
Next to a working gas boiler, the running costs are close: 8.6p a kilowatt hour, where gas runs 7.5 to 8.7p. That is near parity, not a saving, and an honest installer says so before you sign anything. If someone promises your gas bill will fall through the floor, ask them for their sums.
Where the money is actually saved in winter is zoning: heating the one room you sit in instead of the whole house. Where the system earns its keep outright is anywhere already running on electric resistance, and the month gas can never touch.
Rooms differ. Walls differ. A solid-wall Victorian terrace loses heat at a different rate to a new-build, and a room facing north is not the room facing south. We size the system to the room, not to a national average.
So the process stays simple. A survey at your home, then a fixed quote, one figure, in writing. That is the price.
Fern Climate is run by its founders, Hom and Simon. If you speak to us, you're speaking to the people who do the work.