HVAC Air Filter Size Guide Calculator
Filter Size & Airflow
Verify your filter size handles your system airflow
MERV Rating Guide
Understand MERV ratings and choose the right filter
Formula
Face Velocity = CFM / Filter Area (sq ft) | System CFM = Tons x 400 | Max velocity: 300 FPM (1"), 500 FPM (4")
Frequently Asked Questions
How do I find my air filter size?
Check the existing filter for printed dimensions (e.g., 20x25x1). If no filter is installed, measure the width, height, and depth of the filter slot in your furnace or air handler. Round to the nearest standard size. Common residential sizes are 16x25x1, 20x25x1, and 20x20x1.
What MERV rating should I use?
MERV 8-11 provides the best balance of filtration and airflow for most homes. MERV 8 catches large particles and is fine for most people. MERV 11 adds protection against allergens. MERV 13+ is for those with respiratory conditions, but verify your system can handle it.
How often should I change my air filter?
1-inch filters: every 1-3 months. 2-inch filters: every 3-4 months. 4-inch filters: every 6-9 months. 5-inch media filters: every 9-12 months. Check monthly and replace when visibly dirty. Homes with pets or allergies should change more frequently.
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