The short answer
For a constant input, hourly cost equals input kW multiplied by your tariff. A fan provides airflow, while an air conditioner transfers heat; their running costs do not measure the same cooling result. Compare suitable operation and use measured energy when cycling makes rated watts unrepresentative.
Price the electrical draw, then consider the job
At a given tariff, lower electrical input uses less charged energy over the same uninterrupted time. A fan and an air conditioner can therefore have very different running costs.
They also do different things. The European Commission describes comfort fans as providing airflow that helps people feel cooler. ENERGY STAR describes AC as transferring heat from indoors to outdoors. A cheap airflow calculation does not establish equivalent room cooling.
An illustrative eight-hour comparison
Consider two illustrative constant-input scenarios at £0.28/kWh. Neither wattage represents an average for all products.
| Scenario | Input | Energy over 8 hours | Electricity cost |
|---|---|---|---|
| Fan | 30 W | 0.24 kWh | £0.0672, about £0.07 |
| AC | 1,000 W | 8 kWh | £2.24 |
Across 30 identical use days, the fan scenario uses 7.2 kWh and costs £2.02 when rounded. The AC scenario uses 240 kWh and costs £67.20.
These are energy calculations. They do not measure how either appliance affects a particular room, or show that the fan can replace the AC for every condition.
Keep enabled time and input time distinct
The table assumes each entered draw continues for all eight hours. Actual AC compressor and fan operation can change during a session. Fan input can also differ between settings.
Use the electricity calculator for the fan’s appropriate electrical input and time. Use the AC calculator for an AC input estimate or complete-day measurement.
For measured mode, record accumulated energy across complete days that include the routine you intend to repeat. Do not reduce the measured result again for an assumed compressor duty cycle.
Compare routines that achieve the intended result
Keep a record of which room was used, the starting conditions, selected settings and the result you needed. An experiment using a fan for short occupied periods is different from keeping a room at a chosen temperature with AC.
If you use both appliances, their combined electricity is the sum of their compatible energy measurements. A theoretical reduction in AC hours needs evidence from the changed routine before it can be counted as a saving.
If one appliance is already included in a whole-room energy sample, avoid adding it again as a separate row.
Interpret the difference at your own tariff
The same kWh difference costs different amounts at different tariffs. Change the rate to the one that applies during your cooling hours; switching the currency setting does not convert that rate.
Read portable and window AC costs to choose a month or cooling-season period, and BTU/h versus input watts to check the AC specification.