Filter replacement
How to Replace a 16×20×1 Furnace Filter
16×20×1 is easy to confuse with 16×25×1. Ordering the longer filter leaves a gap; ordering the shorter one in a 25" slot leaves a bypass leak. Confirm the stamp, then swap.
Updated July 2026 · 3 min read · Canada
Symptoms
- Filter too loose or too tight in the rack
- Dust after every change
Likely causes
- Wrong size ordered
- Overdue media
What to do
1. Verify 16×20×1 on the old frame
If the print is gone, measure length and width to the nearest ⅛" before ordering.
2. Install with the arrow toward the blower
Seat fully. A 16×20 that rattles usually means you need a different nominal size.
Stop and call a pro when
- No standard size seals the rack
- You have a 2" or 4" cabinet instead
Related guides
- Replace 16×25×1 Filter — Quick homeowner steps to change a 16x25x1 furnace or air handler filter, plus MERV guidance and multipack links.
- Filter Size Guide — How to read furnace filter dimensions, why nominal vs. actual sizes differ, and which MERV rating to buy without starving airflow.
FAQ
Why does my 16×20 look smaller than the label?
Nominal sizes are rounded up. Actual cardboard is slightly undersized on purpose.
Need a licensed tech instead?
If the guide says to stop — or the part swap did not clear the fault — get free quotes from licensed local HVAC contractors.
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