20x20x4 Air Filter Guide

What the size means

20x20x4 is the nominal width × height × depth. The actual dimensions are often slightly smaller, so compare the exact measurements printed on the filter or cabinet label.

Before ordering

1. Remove the current filter and read the size on its frame.
2. Confirm the order of the numbers.
3. Check that the final number matches the cabinet depth.
4. Choose a MERV rating supported by your HVAC system.

Common MERV choices

MERV 8 is often used for routine dust and pollen, MERV 11 for a stronger balance that may help with pets and common allergens, and MERV 13 for finer-particle concerns when the system supports it.

Replacement timing

Many 4-inch media filters can last longer than standard 1-inch filters, but inspect them regularly and follow the cabinet or filter manufacturer instructions.