20x25x1 vs 20x25x4 (and the 20x25x5 Trap): Which Filter Fits?
Quick answer
They share a 20 × 25 face. A 20x25x1 is about ¾ inch deep and a standard 20x25x4 is about 3⅝ inches, but media-cabinet filters sold for 20x25 cabinets are about 4⅜ inches deep. Measure the depth of your old filter before you order. [S1] [S2] [S3] [S4]
- Filterbuy cuts its 20x25x1 to 19.5 × 24.5 × 0.75 in and its 20x25x4 to 19.5 × 24.5 × 3.63 in. [S1] [S2]
- Honeywell's 20 × 25 media filter (FC100A1037) is 20 × 24⅞ × 4⅜ in. [S3] Lennox's X6673 (HCF20-11) is nominal 20x25x5, actual 19¾ × 24¾ × 4⅜ in. [S4]
- Filterbuy's rule of thumb: an old filter 3.75 in deep or less → standard 20x25x4; 4.25–4.5 in → a 20x25x5, whatever the label says. [S2]
Actual sizes of filters sold as 20x25
The nominal size is printed on the frame; the actual size is what fits. Rows marked "per Filterbuy" come from Filterbuy's comparison table, not from that brand's own documents.
| Filter | Sold as | Actual size (in) | Source |
|---|---|---|---|
| Filterbuy 20x25x1 | 20x25x1 | 19.5 × 24.5 × 0.75 | [S1] |
| Filterbuy 20x25x4 | 20x25x4 | 19.5 × 24.5 × 3.63 | [S2] |
| Generic big-box pleated 4-inch | 20x25x4 | 3.75 deep (per Filterbuy) | [S2] |
| Filtrete 20x25x4 | 20x25x4 | 19.88 × 24.63 × 4.31 (per Filterbuy, citing 3M's listing) | [S2] |
| Honeywell FC100A1037 (MERV 11) / FC200E1037 (MERV 13) | 20 x 25 media filter | 20 × 24⅞ × 4⅜ | [S3] |
| Carrier / Bryant EXPXXFIL0020 | 20x25x4 | 4.38 deep (per Filterbuy) | [S2] |
| Lennox X6673 (HCF20-11, MERV 11) | 20x25x5 | 19¾ × 24¾ × 4⅜ | [S4] |
1-inch vs 4-inch vs 5-inch media filter
| 20x25x1 | 20x25x4 (standard) | 20x25 media-cabinet filter | |
|---|---|---|---|
| Typical depth | 0.75 in [S1] | 3.63–3.75 in [S2] | about 4⅜ in [S3] [S4] |
| Where it goes | Return grille or 1-inch furnace slot | 4-inch slot or cabinet | Matching media cabinet (e.g. Honeywell F100/F200, Lennox HCC20-28) [S3] [S4] |
| Replacement guidance | Lennox: change standard 1-inch filters every 3 months [S5] | Filterbuy says 6–12 months for its 20x25x4 (its own claim) [S2] | Honeywell: every 6 months, at least yearly [S3]; Lennox: up to 12 months [S4] |
Filterbuy's depth check
How to tell which one you have
- Measure the old filter's depth, from one edge of the frame to the other. Filterbuy's rule above sorts out most 4-inch and 5-inch mix-ups. [S2]
- Look for a boxed cabinet with a model sticker. Honeywell F100/F200 and Lennox Healthy Climate cabinets take their own 4⅜-inch filters. [S3] [S4]
- No old filter? Measure the slot. A properly sized filter covers the duct opening and lies flush. [S6]
- Install with the arrow toward the furnace or air handler. [S5]
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
Is a 20x25x4 filter actually 4 inches thick?
Usually not. Filterbuy's 20x25x4 is 3.63 inches deep, and Filterbuy says some brands print 20x25x4 on filters that are about 4.38 inches deep. [S2] Honeywell's 20 x 25 media filter is 4⅜ inches deep. [S3]
Can I put a 20x25x4 in a 20x25x5 cabinet?
Filterbuy says no, because a filter that's too shallow leaves a gap that unfiltered air flows through. Buy the depth the cabinet was built for. [S2]
What does a Lennox HCC20-28 cabinet take?
Lennox lists nominal 20x25x5 filters with an actual size of 19¾ × 24¾ × 4⅜ in. The MERV 11 replacement is X6673, MERV 13 is 19L17, and MERV 16 is X6675. [S4]
Should I switch from a 20x25x1 to a 20x25x4?
Only if your slot is built for the deeper filter. The DOE Building America guide recommends the thickest filter your slot can take, because deeper pleats give more surface area and better airflow for longer. [S6]
What MERV rating should I use?
EPA recommends at least MERV 13, or as high as your system fan and filter slot can handle. [S7]
What we could not verify
- Filtrete, Carrier/Bryant and generic 4-inch depths come from Filterbuy's comparison table. We haven't yet checked 3M's or Carrier's own spec sheets.
- Filterbuy's 6–12-month life for its 4-inch filter is the company's own claim.
- We didn't measure any filters ourselves.
Sources
- [S1] 20x25x1 Air Filters — Filterbuy. Accessed 2026-10-24. Used for: Filterbuy 20x25x1 actual size.
- [S2] 20x25x4 Air Filters — Filterbuy. Accessed 2026-10-24. Used for: Filterbuy 20x25x4 actual size, depth-by-brand table, depth rule of thumb, service-life claim.
- [S3] Honeywell Media Air Cleaners Professional Installation Guide (68-0239EF-12, Rev. 10-17) — Honeywell International (PDF hosted by Build.com). Accessed 2026-10-24. Used for: FC100A1037/FC200E1037 actual size, replacement interval.
- [S4] Healthy Climate HCC Media Air Cleaners product specifications (Form 210450, February 2026) — Lennox Industries. Accessed 2026-10-24. Used for: HCC20-28 filters, X6673/19L17/X6675, actual size, service life.
- [S5] Air Filters — Lennox Residential. Accessed 2026-10-24. Used for: 1-inch filters every three months; arrow direction.
- [S6] 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: Thickest filter the slot accepts; measure the slot; flush fit.
- [S7] What is a MERV rating? — U.S. EPA. Accessed 2026-10-24. Used for: MERV 13 recommendation.
Last checked 2026-10-24. Spot an error? Tell us and we'll recheck it against the source.