Extractor Fan Running Cost Calculator
Estimate the electricity cost of a bathroom, kitchen or utility extractor fan, including timer overrun, boost use and low-power continuous ventilation.
Enter Fan Use
Your Extractor Fan Cost
The yearly electricity cost will appear here.
How To Use The Extractor Fan Calculator
1Find Watts
Look for the fan wattage on the label, manual or product page. A small bathroom fan may be under 20 W, while a cooker hood can be higher.
2Add Timer Overrun
If the fan runs for 10 or 20 minutes after the light goes off, include that time in the minutes per run field.
3Use Trickle Power
Continuous fans may use a very low wattage all day. Enter that in the trickle field instead of guessing a daily run count.
4Check Boost
Some fans have a higher boost speed after showers or cooking. Add boost watts and minutes only if they are separate from the main entry.
What The Result Means
The main figure is the annual electricity cost for the pattern you entered. It includes main run time, optional continuous trickle ventilation and optional boost use. The daily and monthly figures help show whether the cost is material on a household bill. For many intermittent bathroom fans, the cost is only a few pounds a year. For continuous ventilation, the annual kWh can be higher even when the wattage looks small because the fan runs every hour.
The cost result is not a recommendation to switch a ventilation system off. Extractor fans remove moisture, smells and combustion by-products where relevant. In bathrooms, poor extraction can contribute to condensation and mould. In kitchens, an extractor or cooker hood can remove steam and cooking odours. Use the calculator to read the energy cost, then balance it with air-quality, moisture and building needs.
Formula And Method
Main kWh = fan watts x runs per day x minutes per run x days per year / 60000.
Trickle kWh = trickle watts x 24 x days per year / 1000.
Boost kWh = boost watts x boost minutes per day x days per year / 60000.
Total kWh = main kWh + trickle kWh + boost kWh.
Running cost = total kWh x electricity unit rate.
The default unit rate is an editable Ofgem price-cap style electricity figure for England, Scotland and Wales direct debit customers in the second quarter of 2026. Enter your own tariff for a bill-specific result.
Worked Extractor Fan Examples
Bathroom Timer Fan
An 18 W fan running four times a day for 25 minutes uses about 11 kWh a year. At 24.67p per kWh, the yearly cost is low, but the overrun time still matters when comparing settings.
Continuous Low-Speed Fan
A 5 W continuous fan uses about 44 kWh a year before boost. The wattage is small, but all-day operation makes it more visible than an occasional fan.
Kitchen Cooker Hood
A higher-powered cooker hood used for short cooking periods can cost more per hour but may still have a modest annual total if use is brief.
Typical Fan Inputs To Try
Timer settings can change the result more than the wattage suggests. A 15 W fan running for 30 minutes after every shower may cost more than the same fan on a 10-minute overrun. If the fan has a pull cord, humidity sensor or separate boost switch, run two estimates: one for normal daily use and one for winter weeks when drying clothes indoors makes the fan run longer.
If the fan is noisy, dirty or slow to start, a cost estimate will not solve the maintenance issue. Clean grilles, blocked ducts and worn bearings can reduce airflow while still using electricity.
| Fan Type | Common Wattage Area | Useful Input Pattern | Cost Note |
|---|---|---|---|
| Small bathroom axial fan | 10 W to 25 W | Several runs per day with timer overrun. | Usually low annual cost unless the timer is very long. |
| Continuous dMEV fan | 3 W to 10 W at trickle speed | Use trickle watts for 24-hour running, then add boost separately. | Small wattage, but many hours. |
| Kitchen extractor or cooker hood | 50 W to 200 W plus lights on some models | Short higher-power use after cooking. | Check whether lamp wattage is included. |
| Utility room fan | 10 W to 40 W | Timer or humidity use after washing and drying. | May run more in winter if clothes dry indoors. |
FAQ
Do extractor fans use a lot of electricity?
Most small extractor fans use little electricity per hour. Continuous fans can still add up because they run for many hours.
Should I turn the bathroom fan off to save money?
Do not switch off ventilation without considering condensation, mould and the reason it was installed. The calculator shows cost, not indoor-air advice.
Does the calculator include the light in a cooker hood?
Only if you add the light wattage to the fan wattage. Some cooker hoods have separate lamp ratings.
What if my fan has a humidity sensor?
Estimate the average minutes it runs each day, or use the continuous trickle and boost fields if the fan has two speeds.
Does standing charge matter?
No for this calculation. A fan changes the kWh used, not the daily standing charge.
Why is my result so small?
Extractor fan wattage is often low. A short 15 W run uses far less energy than heating, hot water, cooking or tumble drying.
Sources
- Ofgem. (2026). Energy price cap explained. Ofgem. https://www.ofgem.gov.uk/information-consumers/energy-advice-households/energy-price-cap-explained
- Energy Saving Trust. (n.d.). Home ventilation and damp. Energy Saving Trust. https://energysavingtrust.org.uk/
- HM Government. (2021). Approved Document F: Ventilation. GOV.UK. https://www.gov.uk/government/publications/ventilation-approved-document-f