Advanced options
The physics divide: fans don't cool air, they cool YOU (moving air evaporates sweat: worth 3-4C of perceived temperature for 50W): air con actually refrigerates the room at 20x the power. The free stack first: windows shut + curtains drawn on the sun side by day, everything open at night, fan in the window blowing OUT at dusk (exhausts the day's heat). A portable AC's exhaust hose must go OUT of a window: run it hoseless and it heats the room it's cooling.
What The Fan vs Air Con Calculator Works Out
- Fan: 50W x hours of cooling x hot days, divided by 1,000 for kilowatt-hours and multiplied by your rate (defaulting to the current Ofgem price cap unit rate). A pedestal or tower fan draws 40W to 70W and cools you rather than the air, worth 3C to 4C of perceived temperature. Eight hours across thirty hot days is GBP 3 to GBP 4 a summer.
- Portable air con: the same hours at 1,000W, the power a portable unit draws to actually refrigerate the room. The same summer costs GBP 65 to GBP 80 in electricity, roughly 20x the fan, plus GBP 300 to GBP 600 to buy.
- The honest verdict: the fan plus the free stack (sun-side windows and curtains shut by day, everything open at night, a window fan blowing out at dusk) handles all but the worst week of most British years. Air con earns its kilowatt for heatwave sleep, top-floor flats, home offices and the medically heat-vulnerable.
- Fan and air con power (advanced): edit for your actual units. Portables run 800W to 1,200W; ceiling fans 15W to 75W; desk fans as little as 20W.
- Compressor duty cycle (advanced): once a correctly sized unit reaches its set temperature the compressor cycles, typically 50% to 80% of the time. An undersized unit runs flat-out at 100% forever.
- Per hot day (advanced): each appliance's cost and kilowatt-hours for one day's cooling at your hours.
- Air con all-in and per summer (advanced): the purchase price plus electricity over the summers you keep it, and the same total spread per summer against the fan's running cost. Buying in January costs meaningfully less than the heatwave-week panic price.
- Installed split system (advanced): a wall-mounted split system at GBP 1,500 to GBP 3,000 installed delivers the same cooling for about half the electricity of a portable. The card shows whether it beats the portable all-in over your chosen summers.
- Fan for the price of the air con (advanced): how many summers of fan running the air con's all-in cost would buy. The exhaust hose is non-negotiable physics: run a portable hoseless and it heats the room it bills for cooling.