Our Tier1 air filter grilles are constructed to ensure air to flow effortlessly between your ventilation systems and your interior rooms. The filters are easy to replace, and larger media capacity provides highly efficient dust particle capture. Nominal size 18 x 30 x 4 inches. Actual size 17 3/4 x 29 3/4 x 3 3/4 inches. No assembly required, the filter should easily slide right in! Improve your overall air quality and circulation in your home with a Tier1 air filter grille. Order today!