The Lennox X6675 (HCF20-16) whole-house filter is labeled “20x25x5” but actually measures ~20 x 24.8 x 4.375 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.
Dealer and reseller sources disagree on the first dimension (19⅝" vs 20¾"). No manufacturer spec sheet found for this exact figure — based on consistent independent reseller measurements.
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.