21 1/2x23 3/8x1 Aerostar Air Filter

A 21 1/2 x 23 3/8 x 1 nominal return takes a filter sized at 21 1/2" x 23 3/8" x 3/4" actual, which this Aerostar matches exactly. Custom and semi-custom HVAC installations spec dimensions like this when the original return opening doesn't conform to a standard nominal size. MERV 8 covers baseline residential filtration: dust, pollen, lint. MERV 11 handles pet households and mild allergy concerns. MERV 13 captures fine particulates including bacteria, virus carriers, and wildfire smoke - the grade for households with respiratory health concerns. Pleated synthetic media with an electrostatic charge built into the fibers handles the filtration. The pleats provide substantially more surface area than a flat fiberglass filter would at the same nominal size, which is what extends the service life to 60 to 90 days under typical residential conditions. The electrostatic charge catches sub-micron particles where the physical weave alone reaches its limits. Manufactured in the USA by Con-Air Industries at the Orlando, Florida facility. Cardboard frame, reinforced to hold shape under blower suction. Odd-size filters benefit most from dimensional precision because an off-spec filter leaves gaps for unfiltered air to bypass the media, which undermines higher MERV grades.