Furnace filter size
24x24x4 air filter
A 4-inch media filter for large filter cabinets.
- Nominal size
- 24x24x4
- Usual actual size
- 23-1/2 x 23-1/2 x 3-3/4 in
- Thickness
- 4 inch
- Change it
- Every 6 months
Makers differ by up to about a quarter inch. Shop by the nominal size.
Which MERV to pick
MERV 11 to 13 is common for 4-inch media filters. The deep pleats keep airflow up even at the higher ratings.
How often to change it
Every 6 months is a good start for a 4 inch filter. Pets, allergies, a remodel or wildfire smoke shorten it; a filter that has turned grey is due whatever the date.
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24x24x4 questions
What is the actual size of a 24x24x4 filter?
Usually 23-1/2 x 23-1/2 x 3-3/4 inches. 24x24x4 is the nominal size, rounded up, and it is the size to shop by. Makers differ by up to about a quarter inch. Shop by the nominal size.
How often should I change a 24x24x4 filter?
Every 6 months is a good start for a 4 inch filter. Change it sooner with pets, allergies, construction dust or wildfire smoke, and whenever it has turned grey.
What MERV rating should a 24x24x4 filter be?
MERV 11 to 13 is common for 4-inch media filters. The deep pleats keep airflow up even at the higher ratings.
Can I use a 24x24x1 instead?
Not in a 4 inch cabinet. A 1-inch filter leaves a gap that lets air go around it, so the dust skips the filter. Match the thickness printed on your current filter.
Get a text when it is due
Free. We will text or email you when this filter is due, with a link to this size.