Free HVAC Filter Sizing Calculator
Determine the filter face area and quantity needed for an HVAC system based on airflow and maximum face velocity.
CFM
ft/min
in
in
Filters Needed
2
Min Filter Face Area4.00 sq ft
Actual Face Velocity173 ft/min
Filters Needed vs System Airflow
Filter Sizing
Face Area = CFM / Face Velocity
Filters = Face Area / Single Filter Area
Keeping face velocity under 300 ft/min ensures good filtration and low pressure drop. Higher velocities reduce filter life and may blow dust through the media.
Example Calculation
1,200 CFM system, 300 ft/min max, using 20x25 inch filters.
- 01Min face area = 1200 / 300 = 4.0 sq ft
- 02Filter area = 20 x 25 / 144 = 3.47 sq ft
- 03Filters = ceil(4.0 / 3.47) = 2
- 04Actual velocity = 1200 / (2 x 3.47) = 173 ft/min
Frequently Asked Questions
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