Industrial Paint Booth Design Calculator

This calculator sizes the ventilation system for a spray paint booth following the airflow logic behind NFPA 33 and OSHA 1910.94. The core figure, required CFM, comes from multiplying the booth's cross-sectional opening area (width times height) by your target face velocity — the speed air must move across that opening to sweep overspray and solvent vapor away from the operator. OSHA sets 100 fpm as the crossdraft minimum, though downdraft booths can run lower (75-125 fpm) and crossdraft booths sometimes need up to 150 fpm depending on the coating's solvent load.

From that same CFM figure, the calculator derives air changes per hour (how many times the entire booth volume gets replaced with fresh air hourly), an exhaust stack diameter sized to keep stack velocity at a fixed 2,500 fpm reference (a typical design target to avoid excessive duct pressure drop while still expelling exhaust cleanly), and the minimum filter bank area needed given your filter's rated face velocity — paint arrestor filters typically run 150-250 fpm. It also estimates the makeup-air heating load: replacing exhausted booth air with outdoor air means that air has to be tempered up to booth setpoint, calculated at the standard air-heating constant of 1.08 BTU per CFM per °F of rise. A fan horsepower estimate rounds it out, assuming a fixed 4 inches water gauge of total static pressure and 65% fan efficiency — real duct runs, filter loading over time, and specific fan curves will shift that number, so use it as a starting point for equipment selection, not a final spec.