How Often to Replace a 21.5x24x1 MERV 8 Air Filter in Winter
Forty-five days. That is the real replacement window for a 21.5x24x1 MERV 8 filter during the heating season — and after tracking filter performance across multiple winters, we can tell you exactly why the 90-day calendar printed on most filter boxes stops working when your furnace runs six to eight hours a day. For most … Read more