What standard does this calculator follow?

The calculations are based on NFPA 92: Standard for Smoke Control Systems. Pressurization flows use the leakage-area approach from Chapter 6; exhaust flows use the mass-flow equations from Chapter 5.

What is the recommended pressure differential for stairwell pressurization?

NFPA 92 recommends a minimum pressure differential of 0.05 in. w.g. (12.5 Pa) across a closed door when sprinklered, and 0.10 in. w.g. (25 Pa) in non-sprinklered buildings. The maximum is typically 0.35 in. w.g. (87 Pa) to allow door opening.

What door leakage area should I use?

NFPA 92 Table B.1 lists typical values. A standard 36-in. × 84-in. door has roughly 0.5–1.0 ft² (0.046–0.093 m²) of total leakage area depending on gaps and undercut. Use 0.5 ft² for well-fitted doors and 1.0 ft² for looser fits.

Does this replace a full engineering analysis?

No. This tool provides estimates for preliminary sizing and concept verification. A licensed fire protection engineer should perform the detailed design, considering all leakage paths, wind effects, stack effect, HVAC interactions, and AHJ requirements.

What is the smoke layer height used for in exhaust calculations?

The exhaust rate must remove smoke fast enough to keep the smoke layer above the design evacuation height (typically 6 ft above the floor). The NFPA 92 mass-flow equations use smoke layer height and fire size to compute the smoke production rate.

Smoke Control Airflow Calculator

Calculate required airflow for building smoke control systems using NFPA 92 pressurization and exhaust methods.

Smoke Control Parameters

Control Method

Number of Closed Doors

Closed doors from the pressurized space to adjacent zones

Door Leakage Area per Door (ft²)

NFPA 92 Table B.1: 0.5 ft² (fitted) to 1.0 ft² (loose)

Design Pressure Differential (in. w.g.)

Sprinklered min 0.05; non-sprinklered min 0.10; max ~0.35

Additional Leakage Factor (unitless, 1.0–3.0)

Accounts for wall/ceiling leakage — NFPA 92 §6.4 typically 1.5×

Enter parameters and click Calculate to see results.

Results

Required Airflow

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CFM (ft³/min)

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m³/s

Parameter	Value

Note: Results are preliminary estimates based on NFPA 92. A licensed fire protection engineer must perform the final design.

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Summary

This calculator uses NFPA 92 methodology to determine required airflow rates for building smoke control systems. It covers three approaches: stairwell pressurization, elevator shaft pressurization, and atrium or large-space smoke exhaust. Enter your building geometry and design parameters to get supply or exhaust airflow in both imperial (CFM) and SI (m³/s) units.

How it works

Select the smoke control method: stairwell pressurization, elevator shaft pressurization, or smoke exhaust.
Enter building parameters such as floor area, ceiling height, number of doors, and leakage area.
Specify design conditions including pressure differential and ambient temperature.
The calculator applies NFPA 92 formulas to compute required supply or exhaust airflow rates.
Review results in both CFM and m³/s, along with intermediate values for verification.

Use cases

Design stairwell pressurization systems to keep egress paths smoke-free during a fire.
Size smoke exhaust fans for large atria, shopping malls, and open floor plans.
Verify elevator hoistway pressurization meets code requirements.
Estimate airflow needs early in a project for mechanical system layout.
Cross-check contractor submittals against NFPA 92 requirements.
Provide quick parametric studies when changing building geometry.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu