The GeneralAire 4551 (ReservePro) whole-house filter is labeled “20x25x5” but actually measures 19.625 x 24.1875 x 4.9375 inches. Unlike 1″ filters, 4″/5″/6″ whole-house filters don't share one universal nominal-to-actual conversion — always match by brand and model, not just the printed size.
MERV 11 cartridge for GeneralAire 4501/4511 whole-house media cabinets, replacing the older #4501 filter. This is from the manufacturer's own spec sheet.
Match by brand + model, not nominal size. Confirm against your old filter or equipment manual before ordering.
Looking for a 1″ furnace filter instead? Use the full FilterKey tool.