Quick answer: convert watts into cost
| Schedule | Energy | Cost |
|---|---|---|
| One hour | 0.025 kWh | $0.0045 |
| One hour/day for 30 days | 0.75 kWh | $0.14 |
| One hour/day for 365 days | 9.125 kWh | $1.64 |
| Continuous for 30 days | 18 kWh | $3.24 |
These calculations describe the fan’s direct electricity only. They do not establish how long a particular bathroom needs ventilation.
Identify all functions in the unit
Check whether one wall control operates the fan alone or also a light, night-light or heater. A total appliance rating may cover several functions that are not always active together. Record mode-specific power where the documentation provides it.
For a fixed installation, use manufacturer data or appropriate existing monitoring. Do not open wiring or try to attach a household plug meter. Ask the landlord or maintenance provider for the model information if the label is inaccessible.
Calculate the schedule you use
At an assumed 25 W, one hour a day for 30 days equals 0.75 kWh. Multiplying by $0.18/kWh gives $0.135. If the same fan is required to run continuously, 24 hours daily would instead use 18 kWh and cost $3.24 in that 30-day example.
These are illustrative constant-power calculations. They do not define the ventilation schedule your bathroom or building needs. Use the actual controls and instructions for that decision.
Compare airflow as well as watts
ENERGY STAR ventilation criteria consider airflow per watt, sound and installed performance. Two fans with different airflow are not interchangeable simply because one has lower electrical input. The duct arrangement and the installation requirements also matter.
If moisture is not clearing as expected, document the problem. A lower speed or shorter timer that leaves persistent dampness is not a useful efficiency improvement.
Keep the estimate in proportion
Add separately measured or documented lighting use if you want the total bathroom fixture cost. Do not omit necessary ventilation to avoid a few cents of fan electricity. A renter’s practical next step may be reporting a failed fan or asking for a suitable control, rather than buying a replacement. Compare observed humidity and normal operation after authorized maintenance, with the cost estimate serving as a budget aid rather than a ventilation specification.
Fan, light and heater are different loads
If one fixture contains several functions, calculate each function using its own watts and operating time. For example, a 25 W fan for one hour and a 10 W light for 30 minutes use 0.030 kWh together. At $0.18/kWh that session costs about half a cent.
| Function | Required input |
|---|---|
| Fan | Mode-specific watts and fan runtime |
| Light | Lamp watts and lighting runtime |
| Heater | Heater input and heat runtime |
| Automatic control | Observed or documented operating schedule |
Do not use the combined maximum rating as though every function runs continuously unless that is the scenario you intend to model.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.