AIR FILTERS Pleated, Poly-Fiber, and Specialty Filters

Most furnace filters have two sets of dimensions: Nominal and Actual. If your furnace filter has actual measured dimensions of 15½" x 24¾" x ¾", you would search based on the nominal dimensions of 16" x 25" x 1".

When determining the size of furnace filter you need, it is best to measure each dimension of your existing furnace filter, and then find the closest nominal match. To find the nominal dimensions of your furnace filter, you should round the actual dimensions of your furnace filter up to the nearest 1" on each side.

When measuring your furnace filter, the height & width are interchangeable:

16" x 25" x 1" is the same as 25" x 16" x 1"

You want your furnace filter to fit snugly, without having to force it into place (this can cause the furnace filter to tear or buckle, which could destroy the filter, or reduce its effectiveness). If, after installation, you find that there is air leaking around your furnace filter, you can add furnace filter gasket tape around the edges of your furnace filter to fill in the gaps.