The Lennox X8788 whole-house filter is labeled “20x26x5” but actually measures 20 x 26 x 5 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 16 filter for the Lennox Healthy Climate PureAir PCO20-28 whole-house purification system — a distinct system from the X6675 cartridge. 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.