AeroStar 12x18x1 Air Filter

Actual dimensions on the 12x18x1 Aerostar come in at 11 3/4" x 17 3/4" x 3/4", so the filter drops into a nominal 12x18x1 return without binding against the grille edges. That tighter actual size is what filter manufacturers have used for decades, and it's why measuring your existing filter rather than your return opening is the only reliable way to verify fit. Available in MERV 8 for standard household dust and pollen, MERV 11 for pet owners and mild allergy households, and MERV 13 if you're fi