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Measure your existing filter or the filter slot opening
Buying the wrong size air filter is one of the most common HVAC mistakes homeowners make. It seems simple enough—just grab any filter that looks about right—but using the wrong size can actually damage your system and hurt your air quality.
A filter that's too small lets unfiltered air bypass around the edges. Too large and it won't fit properly, potentially collapsing into the ductwork. Either way, you're not getting the filtration you're paying for, and your system is working harder than it should.
Our filter size finder helps you determine the exact dimensions you need. No more standing in the filter aisle guessing, and no more returns because you grabbed the wrong size.
There are several ways to determine your correct filter size:
A correctly sized filter captures dust, allergens, and particles effectively without gaps for air to bypass.
The filter protects your HVAC equipment from dust buildup that can damage components and reduce efficiency.
A properly fitting filter maintains correct airflow, preventing your system from working harder than necessary.
When your filter fits correctly, more contaminants are captured, improving your indoor air quality.
Mistake: Buying by brand instead of size
Solution: Filter brands use different sizing conventions. Always verify the actual dimensions match your needs.
Mistake: Forcing an ill-fitting filter
Solution: If you have to bend or force a filter in, it's the wrong size. Gaps around the edges defeat the purpose.
Mistake: Using the highest MERV rating possible
Solution: High MERV filters restrict airflow. Most residential systems work best with MERV 8-11. Higher ratings may require system modifications.
Mistake: Forgetting filter depth
Solution: Filters come in 1, 2, 4, and 5-inch depths. Using the wrong depth means it won't fit in your filter slot.
Some filter situations require professional assessment:
Filter sizes are listed as length × width × depth in inches. A 20×25×1 filter is 20 inches long, 25 inches wide, and 1 inch deep. These are nominal sizes—actual dimensions are slightly smaller.
No. Using the wrong size allows unfiltered air to bypass the filter, reducing air quality and potentially damaging your system. Always use the exact size specified.
For most homes, MERV 8-11 provides good filtration without excessive airflow restriction. If you have allergies or respiratory issues, MERV 11-13 may help, but verify your system can handle the higher restriction.
It depends on your needs. Basic fiberglass filters protect your equipment but don't filter small particles well. Pleated filters (MERV 8+) capture more allergens. For most homes, mid-range pleated filters offer the best value.
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