Enclosure Ventilation Calculator

Design the exhaust for a new enclosure, or audit an existing one from measured openings and airflow. Both modes check EPA Method 204 permanent total enclosure criteria.

Mode

DesignVentilation targets for an enclosure that isn’t built yet. AuditVentilation targets for an enclosure already in place.

Enclosure description (optional)

A name for this enclosure, such as a booth or line number.

Length

Inside dimension.

Width

Inside dimension.

Height

Inside dimension.

NDO %

Percent of surface area that is open. Try smaller values to see the airflow drop.

Face velocity into enclosure

Design air velocity inward through the NDOs.

fpm

Minimum duct transport velocity

Used to size or check the exhaust duct.

fpm

Supply air into enclosure

Makeup air delivered into the enclosure.

CFM

Required exhaust

CFM Q Out

Surface area ft²

Volume ft³

NDO area ft²

Effective NDO %

Air changes per hour ACH

Duct size calculated in

Stock duct size in

Velocity in stock duct fpm

NDO ≤ % of surface area

Face velocity ≥ fpm

Airflow by NDO size

Same enclosure, face velocity and supply air. Smaller openings need less exhaust and a smaller duct.

NDO	NDO area	Q Out	Stock duct	ACH

CriteriaThe 5% NDO and 200 fpm face velocity criteria come from EPA Method 204 (40 CFR Part 51, Appendix M).

Transport velocity2,000 fpm is for vapors and gases; particulate typically needs 3,500–4,500 fpm (ACGIH Industrial Ventilation manual).

Screening onlyThis is a screening calculator; final design should be reviewed by a qualified person.