Filter replacement
How to Replace an 18×24×1 Furnace Filter
18×24×1 shows up on side-return furnaces and hallway grilles. Misreading it as 16×25 is common; measure twice, then keep a multipack on hand.
Updated July 2026 · 3 min read · Canada
Symptoms
- Gaps beside the filter
- Filter crushed on one edge
Likely causes
- Wrong width ordered
- Deferred maintenance
What to do
1. Read or measure 18×24×1
Confirm both dimensions. 18" vs 16" is the usual mistake.
2. Swap and seal
Arrow toward the furnace. The filter should slide snugly without bowing.
Stop and call a pro when
- Rack is bent and will not hold any standard size
Related guides
- Filter Size Guide — How to read furnace filter dimensions, why nominal vs. actual sizes differ, and which MERV rating to buy without starving airflow.
- Replace 16×25×1 Filter — Quick homeowner steps to change a 16x25x1 furnace or air handler filter, plus MERV guidance and multipack links.
FAQ
MERV-13 or MERV-11 for 18×24×1?
MERV-13 is fine on most modern blowers; step to MERV-11 if you hear whistling or see limit trips.
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