Smoke Heat Exhaust Fan Calculator
Smoke and heat vent airflow for a large-area building.
Enter your values
ⓘ Live results
Results
- Preliminary exhaust estimate
- 60,000 CFM
- Rate used
- 3 CFM/sq ft
- Fans at 50,000 CFM
- 2
- Important
- Final design requires a full smoke control engineering analysis, not this rule of thumb
Quick answer
Mechanical smoke and heat exhaust systems are commonly sized at 2-4 CFM per square foot of the largest smoke compartment, per NFPA 204 style guidance, subject to a full engineering analysis.
CFM = floor area x rate (preliminary estimate only)
How to use the Smoke Heat Exhaust Fan Calculator
- 1Enter the largest single smoke compartment's floor area.
- 2Choose an approximate hazard classification.
- 3Use the result only as an early planning number — smoke control systems require full engineering analysis and commissioning.
Worked example
Using the values the calculator loads with:
Inputs
- Compartment area20000 sq ft
- Hazard classificationOrdinary hazard (3 CFM/sq ft)
Results
- Preliminary exhaust estimate60,000 CFM
- Rate used3 CFM/sq ft
- Fans at 50,000 CFM2
- ImportantFinal design requires a full smoke control engineering analysis, not this rule of thumb
Frequently asked questions
Is this calculator a substitute for a smoke control study?
No — it gives a rough order-of-magnitude figure only; actual smoke exhaust design requires modelling by a fire protection engineer.
Why does hazard class matter?
Higher fuel loads produce more heat release rate, requiring more exhaust to keep smoke layers above occupants.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.