How To Spec An Air Filter

Numerous considerations come into play when designing custom air filters for OEM applications. The following should be reviewed early in the planning process:

• Determine the filtration performance requirements.
• Match filters to air-moving (cfm) requirements.
• Analyze the space available for filters.
• Specify standards and specifications (NEBS, ETSI, CE, UL 60950 (formerly UL 1950), etc.)

Filter Selection Procedure

Many thermal design engineers use the following steps when designing an air filter:

1. Select air filter dimensions (length, width, thickness).
2. Calculate airflow velocity in linear ft./min. using air volume rating of fan in cfm divided by surface area of air filter in sq. ft. (i.e. 200 cfm./0.50 sq. ft. = 400 fpm)
3. Select disposable or reusable media.
4. Use media initial resistance vs. face velocity data/curves for preferred media. Typically, initial resistance is 0.10″ wg (water gauge) or less.
5. Select appropriate air filter model and frame thickness to accept selected media thickness. For example: Disposable, white UFM-50 media fits in any frame thickness (0.30″, 0.43″ or 0.50″). The cleanable/reusable Quadrafoam in 0.25 thickness fits 0.30″ and 0.43″ thick frames and 0.50″ thick Quadrafoam fits in 0.50″ thick frame.)
6. Select a media color. Quadrafoam -green, gray or black. Polyester – white
7. Determine if any handles or other fixtures are necessary for installation / removal.
8. Prepare air filter drawing.