This is the comparison most people quietly make before spending anything: keep buying fans, or finally get air conditioning? The honest answer is that they are not really rivals — they do different jobs. A fan costs pennies a night to run. Air conditioning costs meaningfully more, but it is the only one of the two that actually makes the room cooler. Here is the maths, and the point where one stops being enough.
The bit most comparisons skip: a fan doesn't cool the room
A fan moves air. That's it. It doesn't lower the temperature of the room by a single degree — if anything, the motor adds a small amount of heat. The reason a fan feels good is that moving air helps sweat evaporate from your skin, and evaporation carries heat away from your body. You feel cooler; the room isn't.
That works well in ordinary warm weather. It works much less well on humid nights, when sweat won't evaporate, and in serious heat — once room temperatures get well above body-comfortable levels — the effect fades until a fan is mostly blowing hot air at you. Air conditioning, by contrast, is a refrigeration system: it pulls heat out of the room and dumps it outside. The room genuinely gets cooler and, usefully, drier too.
What each costs per hour
Fans sip electricity. A typical desk or pedestal fan draws a few tens of watts — roughly what an old-fashioned light bulb used. A split air conditioning unit cooling a single room draws several hundred watts on average while it is working, less once the room is down to temperature and the unit is just holding it there. Exact figures depend on the model, the room and the weather, so treat the numbers below as rough worked examples at a unit rate in the mid-20s of pence per kWh — check your own tariff, because it genuinely changes the maths:
| Appliance | Typical draw | Rough cost for 8 hours |
|---|---|---|
| Desk fan | 30–50W | 6–11p |
| Pedestal or tower fan | 40–60W | 8–13p |
| Split AC (one bedroom) | 500–900W average | £1–2 |
| Portable AC unit | around 1,000W | £2 or so |
So yes — running AC costs roughly ten to twenty times what a fan does. Run a fan every night of a long summer and you might spend around a tenner all season. Run a bedroom split through the genuinely hot spells — a few weeks of real use rather than all summer — and you are more likely looking at tens of pounds, not hundreds. We've done the fuller seasonal maths in our guide to AC running costs. Note the portable unit in that table: it tends to cost more to run than a proper split while cooling noticeably worse, which is why we compare the two properly here.
When a fan genuinely is enough
We'd be a poor guide if we pretended everyone needs AC. A fan is honestly fine when:
- Indoor temperatures top out in the mid-to-high 20s and drop back at night
- You can ventilate — windows open at night, curtains closed by day
- The heat bothers you for a handful of days a year, not weeks
- Nobody in the house is especially vulnerable to heat
In that situation, buy a decent quiet fan, point it at the bed, and keep your money. Most British summers, most of the time, that is a perfectly rational answer.
The tipping point
The calculation changes when the fan stops doing its one job. The common triggers we hear:
- Bedrooms in a heatwave. When the room is still stiflingly warm at midnight, a fan just stirs warm air. Broken sleep for a week or two each summer is usually what finally pushes people over the line.
- Home offices. If you work in a warm room every day, weeks of sluggish afternoons start to look expensive in their own way — and lofts and south-facing box rooms run hot.
- Anyone vulnerable to heat. Babies, older people, and anyone with a heart or respiratory condition can be genuinely at risk in prolonged heat. For those households a room that is actually cooler — not one that merely feels breezier — stops being a comfort question.
- Humid nights. Fans rely on evaporation, so muggy heat is exactly when they are weakest. AC dehumidifies as it cools, which is often what makes the biggest difference to sleep.
The upgrade maths, honestly
A single-room split system typically costs somewhere in the low thousands fitted, and a multi-split covering several rooms costs more again — our full cost guide breaks down the realistic ranges and what drives the price. That is real money for something you might use hard for six weeks a year.
Two things soften it. First, a modern split is a reversible air-to-air heat pump: the same unit heats in winter, typically delivering roughly three units of heat or more for each unit of electricity, so it earns its keep year-round rather than sitting idle for ten months. (One honest caveat: air-to-air systems are not covered by the Boiler Upgrade Scheme, which applies to air-to-water and ground-source heat pumps.) Second, a properly installed and serviced unit should last well over a decade, so the fitted cost spreads thin across a lot of summers — and, increasingly, winters.
Our honest summary
If heat is an occasional nuisance, buy a fan and enjoy the pennies-a-night running cost. If it is costing you sleep every summer, affecting your work, or worrying you for someone vulnerable in the house, a fan is treating the symptom — and that is when AC starts to justify itself. If you get to that point, tell us about your home and we'll match you with a vetted local installer for a free, no-obligation estimate — no call-centre round-robin, just a straight answer on what your rooms would cost.