Furnace Filter Size Finder
Find the right filter size for your furnace or AC unit. Enter your filter dimensions or check the size printed on your current filter.
Enter Your Filter Dimensions
How to Find Your Filter Size
Check your current filter
The size is printed on the frame edge (e.g., "16x20x1")
Or measure the filter slot
Measure width × height × depth of the opening
Round to nearest inch
Filters use nominal sizes (actual size is ~1/2" smaller)
Tip: Write your filter size on your furnace or save it in TidyBoss so you always have it when shopping.
Most Common Furnace Filter Sizes
Understanding MERV Ratings
MERV (Minimum Efficiency Reporting Value) measures how effectively a filter captures particles. Higher isn't always better - too high can restrict airflow.
| MERV Rating | Captures | Best For |
|---|---|---|
| MERV 1-4 | Large dust, pollen | Basic protection |
| MERV 8-11 | Dust, pollen, mold, pet dander | Most homes (recommended) |
| MERV 13-16 | Bacteria, smoke, virus carriers | Allergies, newer HVAC systems |
| MERV 17-20 | Viruses, carbon dust | Hospitals, cleanrooms (not homes) |
Warning: Too High Can Damage Your System
Using a MERV rating higher than your system is designed for can restrict airflow, strain your blower motor, and increase energy costs. Check your HVAC manual or ask a technician for the maximum recommended MERV.
How Often to Replace Your Filter
1-Inch Filters
- Standard recommendation: Every 1-3 months
- With pets: Every 1-2 months
- With allergies: Every 1 month
- Vacation home: Every 6-12 months
4-5 Inch Filters
- Standard recommendation: Every 6-12 months
- With pets: Every 4-6 months
- With allergies: Every 3-4 months
Pro Tip: Check Monthly
Hold your filter up to light. If you can't see light through it, it's time to replace. A dirty filter makes your system work harder, increasing energy bills and wear.
Frequently Asked Questions
What if I can't find my HVAC filter size?
Check for a label on the existing filter, inside the filter slot on the HVAC unit, or in your system's owner's manual. If no label exists, measure the filter opening with a tape measure (length x width x depth). Common residential sizes are 16x25x1, 20x25x1, and 16x20x1 inches. Custom sizes can be ordered online.
Are expensive HVAC filters worth it?
Mid-range filters (MERV 8-11, $8-$15 each) offer the best value for most homes—they capture 85-95% of particles without restricting airflow. Premium MERV 13+ filters ($15-$30) are worth it for allergy sufferers or homes with pets. The cheapest fiberglass filters (MERV 1-4, $1-$3) only catch large debris and don't improve air quality.
Can the wrong HVAC filter damage my system?
Yes. A filter with too high a MERV rating for your system restricts airflow, causing the blower motor to work harder, increasing energy bills, and potentially freezing the evaporator coil. Most residential systems handle up to MERV 13. Check your HVAC manual for the maximum recommended MERV rating, or ask your HVAC technician.
Related Resources
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