Balanced Comfort 20x20x3 MERV 13 Return Air Grille Filter (2 PACK) filter uses a unique design. The one inch return grille filters are not as efficient as the MERV 3" filters and can become clogged quickly. You might want to consider upgrading your filter when you install a new air conditioner or put in an additional system for higher efficiency, which will last longer without needing replacement so often!