Paint Booth Airflow Calculator

Spray booth ventilation sizing starts with a simple relationship — required CFM equals the booth's effective cross-sectional area times the target face velocity in feet per minute — but this calculator adjusts that cross-section based on how air actually moves through your specific booth type. For a cross-draft booth, air passes through the full width-by-height opening, so that's the cross-section used; for a full downdraft booth, air instead moves down through the floor, so the calculator uses width times length instead; a semi-downdraft booth (intake at the ceiling front, exhaust at the floor rear) gets a 15% reduction applied to the width-by-height area to reflect its somewhat less direct airflow path. The calculator checks your target velocity against OSHA 29 CFR 1910.94(c)'s practical minimums by booth type — 100 FPM for cross-draft, 75 FPM for semi-downdraft, 50 FPM for full downdraft, matching OSHA's own rule that "crossdrafts in excess of 100 fpm should not be permitted" — and flags whether you're compliant.

It separately checks exhaust duct velocity against the 3,000 FPM industry threshold needed to keep overspray particulate suspended and moving rather than settling and clogging the ductwork. Fan sizing follows the standard formula relating airflow, static pressure, and fan efficiency (assumed at 65% here), with static pressure built from a filter-loading estimate (higher for higher-efficiency filters) plus a duct-length-scaled resistance term. These figures are solid first-pass sizing numbers for choosing a fan and verifying a booth design meets minimum airflow requirements, but real system static pressure depends on actual ductwork routing, elbow count, and filter condition over time — a licensed mechanical or safety engineer should validate final fan selection and confirm compliance with your local fire code and NFPA 33 before installation.