Available sizes shown in listings include 25 x 20 x 4 inches, a nominal 16 x 28 x 4 (actual about 15 7/8 x 28 3/4 x 4 1/8), and a nominal 20 x 26 x 4 (actual about 20 x 26 x 4 1/8). Listings typically display both nominal and slightly different actual measurements.
Most listings describe these Aprilaire replacement air filters as electrostatic filters made from polypropylene material.
Filters are offered as single packs and multi-packs; the listings show package quantities of 1, 2, and 4.
Most listings use a 4-inch nominal thickness, but actual measurements can differ slightly (for example, listings show actual thicknesses like about 4 1/8 inches or 4.31 inches). In other words, nominal thickness is typically 4 inches but actual size may vary slightly by listing.
Change intervals vary across listings and reviews. Some product text advises changing a 4-inch filter at least once every 12 months, another listing notes a maximum filter life of 3 months, and review summaries often reference an annual replacement cycle. Recommendations are inconsistent between listings.
