By the Numbers
By the Numbers: The Cost of Running a Fan for a 12-Day Heatwave
A 50-watt fan, 12 hours a day, 12 hot days and Ofgem's current unit rate become one transparent appliance-cost example.
The Environment Agency described a spell of 12 consecutive days above 30°C during July 2026. That gives us a practical household electricity question: how much could it cost to run a fan through the whole period?
The answer comes from three inputs: the fan's power rating, how long it runs and the electricity unit rate. The Appliance Running Cost Calculator puts them together.
The story number
The Environment Agency's 21 July drought update said the recent heatwave included 12 consecutive days with temperatures above 30°C.
For the electricity input, Ofgem's average Direct Debit price-cap rate for 1 July to 30 September 2026 is 26.11p per kWh. We use it only as an illustrative unit price.
The number to run
Electrical energy is:
`kWh = watts ÷ 1,000 × hours used`
Cost is:
`running cost = kWh × unit price`
A 50-watt fan running for 12 hours uses:
`50 ÷ 1,000 × 12 = 0.6 kWh per day`
The assumptions
Our central example uses:
- 50W fan
- 12 hours per day
- 12 days
- electricity at 26.11p per kWh
We assume the fan draws its stated power continuously. We exclude the household standing charge because it is not caused by switching on this one appliance.
Run the numbers
For the central example:
- daily energy: 50W ÷ 1,000 × 12 hours = 0.6 kWh
- 12-day energy: 0.6 × 12 = 7.2 kWh
- cost: 7.2 × £0.2611 = £1.88
Here are three scenarios:
| Fan and schedule | Energy over 12 days | Usage cost at 26.11p/kWh |
|---|---|---|
| 35W for 8 hours/day | 3.36 kWh | £0.88 |
| 50W for 12 hours/day | 7.20 kWh | £1.88 |
| 75W for 24 hours/day | 21.60 kWh | £5.64 |
Why appliance type matters
Power rating is the biggest difference between a simple fan and powered cooling equipment. A 1,000W portable air conditioner running for the same 12 hours per day would use:
`1,000 ÷ 1,000 × 12 × 12 = 144 kWh`
At 26.11p per kWh, that is about £37.60 in usage charges.
This is not a comparison of cooling performance. It only shows what a 20-times-higher power rating does to the electricity calculation.
What the result means
A small fan can run for many hours while using relatively little energy because its wattage is low. The same formula also explains why guesses based on appliance size or noise can be misleading: the rating plate is the useful input.
The estimate changes in direct proportion:
- double the wattage, and the energy estimate doubles
- double the hours, and the energy estimate doubles
- a higher unit rate increases the cost but not the kWh
Try your own numbers
Find the wattage on the fan's rating label or manufacturer specification. Enter that value, your expected daily hours and the unit rate from your electricity statement in the Appliance Running Cost Calculator.
The UK Energy Bill Calculator is more suitable for whole-home electricity and gas use. The Ohm's Law Calculator can explain the relationship between power, voltage, current and resistance in simple electrical examples.
Caveats and source notes
- Actual consumption can differ by speed setting, controls, standby use and product design.
- Use the appliance's own rated wattage rather than the examples above.
- Standing charges are part of the household account but not an incremental fan-running cost.
- This article calculates electricity only. It does not assess cooling effectiveness, indoor-temperature safety or health protection.
- Follow official hot-weather guidance where health may be affected.
Sources: Environment Agency, National Drought Group steps up response after third heatwave, 21 July 2026; Ofgem, Energy price cap unit rates and standing charges, accessed 24 July 2026.
