14x25x1 vs 14x24x1: Which One Do You Need?
Quick answer
They're different filters. Filterbuy's 14x25x1 is 13.5 × 24.5 × 0.75 in and its 14x24x1 is 13.38 × 23.38 × 0.75 in, so the 14x25x1 is about an inch longer. Filterbuy says not to use a 14x25x1 in place of a 14x24x1. Order the size printed on your old filter. [S1] [S2]
- Width and depth are almost the same, so the two are easy to mix up on a shelf or in a cart. The length is what's different. [S1] [S2]
- A filter that's an inch short leaves a gap, and Filterbuy says a one-inch gap lets unfiltered air slip past the media. [S2]
- DOE's Building America guide says a properly sized filter covers the whole opening and lies flat, never at an angle. [S3]
14x25x1 vs 14x24x1 at a glance
| 14x25x1 | 14x24x1 | |
|---|---|---|
| Filterbuy actual size (in) | 13.5 × 24.5 × 0.75 [S1] | 13.38 × 23.38 × 0.75 [S2] |
| Filtrete actual size (in) | Not checked yet | 13.68 × 23.68 × 0.81 (per Filterbuy's brand table) [S2] |
| Mann+Hummel actual size (in) | Not checked yet | 13⅜ × 23⅜ × ¾ (per Filterbuy's brand table) [S2] |
| Use it in the other size's slot? | No. Filterbuy says not to substitute it for a 14x24x1 [S2] | No. It's about an inch short and leaves a gap [S2] [S3] |
| Change interval | Lennox: every 3 months for standard 1-inch filters [S4] | Lennox: every 3 months for standard 1-inch filters [S4] |
Which one is yours?
| You measure (long side of the old filter or slot) | Likely size | Source |
|---|---|---|
| About 24½ in | 14x25x1 | [S1] |
| About 23⅜ to 23¾ in | 14x24x1 | [S2] |
| Something else | Check the frame, or measure the slot and compare with the actual sizes above | [S3] |
Actual sizes vary a little by brand, so match the nominal size on the frame first and use the tape measure as a check.
How to tell them apart in a minute
- Read the old filter's frame. The nominal size is printed on it. If that filter fit, buy the same size. [S3]
- Measure the long side. Filterbuy's 14x25x1 is 24.5 inches long and its 14x24x1 is 23.38 inches, so the long side settles it. [S1] [S2]
- No filter in the slot? Measure the opening. The right filter covers it completely and lies flat, never at an angle. [S3]
- Point the arrow toward the furnace or air handler when you put the new one in. [S4]
Related: 16x25x1 vs 16x25x4 and 20x20x1 actual size by brand.
Where to buy
We don't link to specific sellers here yet. Search for the exact part number or size on this page at a retailer you trust, compare the listed actual dimensions, and check the current price. We don't list prices because they change daily.
FAQ
Can I use a 14x24x1 instead of a 14x25x1?
No. A 14x24x1 is about an inch shorter than a 14x25x1 [S1] [S2], and Filterbuy says a one-inch gap lets unfiltered air slip past the media. [S2] DOE's guide says the filter should cover the whole opening. [S3]
What is the actual size of a 14x25x1 filter?
Filterbuy cuts its 14x25x1 to 13.5 × 24.5 × 0.75 inches. [S1]
What is the actual size of a 14x24x1 filter?
Filterbuy's is 13.38 × 23.38 × 0.75 inches. Filterbuy's brand table lists Filtrete's at 13.68 × 23.68 × 0.81 inches. [S2]
My old filter has no size on it. What do I do?
Measure the slot. DOE's Building America guide says the right filter covers the whole opening and lies flat. [S3]
How often should I change a 1-inch filter?
Lennox says to change standard 1-inch disposable filters every three months, or more often with allergies, pets or dust. [S4]
What we could not verify
- Filtrete and Mann+Hummel 14x24x1 sizes come from Filterbuy's table, not from those brands' own pages. We couldn't load 3M's product pages to check them.
- Other brands' 14x25x1 actual sizes. Retail listings we saw gave Filtrete numbers, but not from 3M directly, so we left them out.
- Which furnace or air handler models use each size. Filterbuy names some brands for the 14x24x1, but without model numbers, so we didn't list them.
Sources
- [S1] 14x25x1 Air Filters, Filterbuy. Accessed 2026-10-24. Used for: Filterbuy 14x25x1 actual size.
- [S2] 14x24x1 Air Filters, Filterbuy. Accessed 2026-10-24. Used for: Filterbuy 14x24x1 actual size, brand table (Filtrete, Mann+Hummel), don't substitute a 14x25x1, gaps let air bypass.
- [S3] Replace Air Filter Located in Furnace or Central Heat Pump Air Filter Slot, Building America Solution Center (PNNL, U.S. Department of Energy). Accessed 2026-10-24. Used for: Filter size printed on frame; measure the slot; filter covers the opening and lies flat.
- [S4] Air Filters, Lennox Residential. Accessed 2026-10-24. Used for: Change 1-inch filters every three months.
Last checked 2026-10-24. Spot an error? Tell us and we'll recheck it against the source.