18x18x1 Aerostar Air Filter

An 18x18 nominal return takes a filter that measures 17 1/2" x 17 1/2" x 3/4" actual, and this Aerostar fits that spec. Square 18x18 returns are common in compact residential setups and some smaller air handlers. MERV 8 covers baseline household filtration for dust, pollen, and lint - the standard choice for homes without pets or specific allergy concerns. MERV 11 picks up pet dander, smoke residue, and most common allergens. MERV 13 captures fine particulates including bacteria, smoke from wildfires, and virus-sized droplets. The pleated synthetic media construction gives this filter substantially more capacity than a flat fiberglass throwaway. The electrostatic charge in the fibers catches particles smaller than the physical weave would stop mechanically. Manufactured in the USA by Con-Air Industries, Orlando, Florida. The cardboard frame is reinforced to maintain shape under blower suction - frame collapse is one of the more common failure modes in cheaper filters, and a collapsed frame lets unfiltered air bypass the media entirely. Plan on a 60-to-90-day change interval for MERV 8 and 11 in typical residential use. MERV 13 reaches its pressure-drop limit faster and wants a change closer to every 30 to 60 days under similar conditions.