Ventilation Fan Runtime Calculator
Estimate how many minutes per hour a ventilation fan must run to achieve a target air-change rate, plus daily energy use and cost.
Default project preview
38.1 minutes/hour
Room volume
2,700 ft³
Required average airflow
135 CFM
Delivered fan airflow
212.5 CFM
Continuous-fan ACH
4.72
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Room length
Enter this project assumption in ft. The current imperial default is 20 ft.
Room width
Enter this project assumption in ft. The current imperial default is 15 ft.
Room height
Enter this project assumption in ft. The current imperial default is 9 ft.
Target air changes per hour
Enter this project assumption in ACH. The current imperial default is 3 ACH.
Fan airflow
Enter this project assumption in CFM. The current imperial default is 250 CFM.
Delivered airflow efficiency
Enter this project assumption in %. The current imperial default is 85 %. Minimum: 1. Maximum: 100.
Fan electrical power
Enter this project assumption in W. The current imperial default is 90 W.
Hours ventilation is required
Enter this project assumption in hours/day. The current imperial default is 12 hours/day. Minimum: 0. Maximum: 24.
Electricity price
Enter this project assumption in per kWh. The current imperial default is 0.18 per kWh. Minimum: 0.
How to read the outputs
Room volume
entered dimensions. Default preview: 2,700 ft³.
Required average airflow
3 ACH target. Default preview: 135 CFM.
Delivered fan airflow
85% efficiency. Default preview: 212.5 CFM.
Continuous-fan ACH
at delivered airflow. Default preview: 4.72.
Daily electricity
7.62 run hours/day. Default preview: 0.686 kWh.
Daily energy cost
entered electricity rate. Default preview: $0.12.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Required average airflow = room volume × target ACH ÷ 60. Runtime fraction = required airflow ÷ delivered fan airflow. Daily energy = watts × runtime hours ÷ 1000.
Reviewed project guidance
How to use this estimate in a real project
Last reviewed: July 30, 2026
Estimate fan operating hours and energy use needed to deliver a target daily ventilation volume at an entered airflow.
Calculation steps
- 1Set the target outdoor-air volume or equivalent runtime requirement.
- 2Enter delivered fan airflow.
- 3Divide required volume by airflow.
- 4Calculate electricity from fan watts and operating hours.
Worked numerical example
A 60 cfm fan delivering 7,200 ft³ per day must run 120 minutes daily. At 35 W, that is 0.07 kWh per day before control losses.
Purchasing and rounding
Use controls designed for the ventilation strategy and verify measured airflow after installation.
Interpret the result
Runtime arithmetic does not establish the required ventilation rate or account for infiltration credit.
Page-specific assumptions
- Constant delivered airflow.
- No simultaneous boost mode.
- Fan wattage is representative.
Common mistakes
- Using nameplate rather than measured airflow.
- Confusing cfm with cubic feet per day.
- Ignoring intermittent-control requirements.
Primary and technical references
BuildMeter provides planning estimates, not engineering, architectural, electrical, mechanical, plumbing, permit or code approval. Review the methodology and verify final decisions with product documentation and qualified professionals.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Ventilation Fan Runtime Calculator questions
What happens when runtime exceeds 60 minutes per hour?+
The entered fan is too small to reach the target air-change rate even when running continuously.
Why include delivered airflow efficiency?+
Duct resistance, grilles and installation conditions often reduce airflow below the fan free-air rating.
Is intermittent operation always acceptable?+
No. Required ventilation schedules and moisture control depend on the room use, contaminants and applicable standards.