Calculate exhaust fan power, runtime, fan count or energy use from any 3 values with unit conversion for hours, minutes, kW, W, HP, kWh and Wh.
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Exhaust Fan Formula
The exhaust fan calculator uses energy consumption formulas based on running time, fan power rating, and number of fans. The base units are hours for time, kilowatts for power, and kilowatt-hours for energy consumption.
- E = power consumption in kilowatt-hours (kWh)
- T = time the fan runs in hours
- P = power rating of one fan in kilowatts (kW)
- N = number of fans
To solve for time, power, or number of fans, the same formula is rearranged:
- Power consumption: enter time, power rating, and number of fans to find total energy used.
- Time: enter energy consumption, power rating, and number of fans to find how long the fans ran.
- Power rating: enter energy consumption, time, and number of fans to estimate the power rating per fan.
- Number of fans: enter energy consumption, time, and power rating to estimate how many equivalent fans are represented.
Common Exhaust Fan Power Ratings
Actual fan power depends on size, motor type, speed setting, and installation conditions. Use the nameplate rating when available.
| Fan type or size | Typical power range | Typical use |
|---|---|---|
| Small bathroom exhaust fan | 10 to 40 W | Bathroom or small utility room |
| Kitchen exhaust fan | 40 to 150 W | Residential kitchen ventilation |
| Inline duct fan | 50 to 250 W | Ducted ventilation systems |
| Industrial exhaust fan | 0.5 to 5 HP or more | Workshops, warehouses, factories |
Unit Conversions Used for Exhaust Fan Energy
| Input unit | Base conversion |
|---|---|
| Minutes | 1 minute = 1/60 hour |
| Watts | 1 W = 0.001 kW |
| Horsepower | 1 HP = 0.746 kW |
| Watt-hours | 1 Wh = 0.001 kWh |
Example Calculations
Example 1: Calculate power consumption
You run 2 exhaust fans for 8 hours. Each fan is rated at 75 W.
Convert 75 W to kW:
Apply the formula:
The fans use 1.2 kWh.
Example 2: Calculate running time
An exhaust fan system used 3 kWh. There are 3 fans, and each fan is rated at 0.2 kW.
The fans ran for 5 hours.
FAQ
How do I find the power rating of an exhaust fan?
Check the fan label, motor nameplate, product manual, or specification sheet. The rating may be listed in watts, kilowatts, or horsepower. If the label shows voltage and current instead, power can be estimated by multiplying volts by amps, but the exact electrical consumption may vary because motors are not always 100% efficient.
Does this calculate the cost of running an exhaust fan?
This calculator finds energy consumption in kWh, not cost directly. To estimate cost, multiply the kWh result by your electricity rate. For example, if the result is 1.2 kWh and your rate is $0.15 per kWh, the cost is 1.2 × 0.15 = $0.18.
Why does the number of fans result sometimes include decimals?
The formula treats the number of fans as a mathematical value. A decimal result means the entered energy, time, and power do not match a whole number of identical fans. In real use, the number of fans is normally a whole number, so check the power rating, runtime, and energy value if you expected an integer.
