Furnace Filters
Best 20x24x4 Furnace Filter (2026): 4 Picks Compared
As an Amazon Associate we earn from qualifying purchases. Specs below come from each product's Amazon listing; we do not test products in person.
For a 20x24x4 slot, the Filter King is the pick with that nominal size, a MERV 8 filter in a 5-pack. The Nordic Pure and Filtrete are also 20x25x4 nominal, both rated MERV 12, so measure the slot before ordering.
Starting out? See the main guide: Best Furnace Air Filters
Top picks at a glance
-
Best OverallSimply 20x25x4 Air Filter9.8 View on Amazon -
9.6 View on Amazon -
Also GreatFiltrete 20x25x4 Air Filter9.6 View on Amazon -
Most in the PackFilter King 20x24x4 Air Filter MERV9.2 View on Amazon
Compare the specs
Ranked on pack size from each listing, plus how many buyers have rated it. A dash (—) means we could not confirm that figure from the listing.
| Pick | MERV rating | Pack size | Weight | Warranty |
|---|---|---|---|---|
| 1. Simply 20x25x4 Air Filter | MERV 8 | 4-pack | — | — |
| 2. Nordic Pure 20x25x4 Pleated MERV 12 Air | MERV 12 | 2-pack | — | — |
| 3. Filtrete 20x25x4 Air Filter | MERV 12 | 2-pack | — | — |
| 4. Filter King 20x24x4 Air Filter MERV | MERV 8 | 5-pack | — | — |
Simply 20x25x4 Air Filter
A MERV 8 filter in a 4-pack with up to 3 months of filtration per filter, sized at 20x25x4 nominal.
- MERV rating: MERV 8
- Pack size: 4-pack
Good for
- Buyers who want a 4-pack of MERV 8 filters
- Owners replacing filters every 3 months
Skip it if
- You need a filter for a 20x24x4 slot
- You want a MERV rating above 8
The pleated media uses electrostatically charged synthetic media, and the pack includes 4 filters plus an installation guide. Each filter lasts up to 3 months, and it slides into central units or return grilles following the airflow arrows.
Nordic Pure 20x25x4 Pleated MERV 12 Air
A MERV 12 pleated filter in a 2-pack, equivalent to MPR 1500-1900, with an actual size of 19.5 x 24.5 x 3.63 inches.
- MERV rating: MERV 12
- Pack size: 2-pack
Good for
- Buyers who want MERV 12 filtration in a 2-pack
- Owners with a 20x25x4 filter slot
Skip it if
- You need a filter for a 20x24x4 slot
- You want more than 2 filters in a pack
It uses MERV rated synthetic poly blend pleated media and slides in for installation. The actual size is 19.5 x 24.5 x 3.63 inches against a nominal size of 20 x 25 x 4. The pack holds 2 filters, and the media is made in the USA.
Filtrete 20x25x4 Air Filter
A MERV 12 filter rated MPR 1550 in a 2-pack, with a 12-month change interval and app reminders.
- MERV rating: MERV 12
- Pack size: 2-pack
Good for
- Buyers who want a 12-month filter change interval
- Owners with Honeywell or AprilAire Space-Gard media air cleaners
Skip it if
- You need a filter for a 20x24x4 slot
- You want a pack larger than 2 filters
The exact size is 19.88 x 24.63 x 4.31 inches against a nominal size of 20 x 25 x 4. It captures 50% of small particles from the air passing through it, and the pack holds 2 filters. The Filtrete Smart App sets 90-, 180- or 365-day reminders, and the filter is changed at least once every 12 months.
Filter King 20x24x4 Air Filter MERV
The only pick here with a 20x24x4 nominal size, a MERV 8 filter in a 5-pack that lasts up to 90 days.
- MERV rating: MERV 8
- Pack size: 5-pack, the most here
Good for
- Owners with a 20x24x4 filter slot
- Buyers who want 5 filters in one pack
Skip it if
- You want a MERV rating above 8
- You want a filter that lasts longer than 90 days
The nominal size is 20 x 24 x 4, and the actual size is 19.38 x 23.38 x 3.75 inches. The pleated design traps airborne particles, and the pack holds 5 filters. Installation is open, slide and close, and each filter lasts up to 90 days.
How to choose
Match nominal size to actual size
Here, the Filter King is nominally 20 x 24 x 4 with an actual size of 19.38 x 23.38 x 3.75 inches, while the other three are nominally 20 x 25 x 4. Compare the actual size against the slot in your unit before ordering, since a filter that is too large will not fit.
Compare MERV ratings side by side
MERV rates how well a filter captures particles, with a higher number meaning finer capture. The Simply and Filter King are MERV 8, while the Nordic Pure and Filtrete are MERV 12. The Filtrete also carries an MPR 1550 rating, and the Nordic Pure is equivalent to MPR 1500-1900, so compare MERV to MERV and MPR to MPR rather than mixing the two scales.
Plan the change interval
Change intervals differ across these picks, so match the interval to your replacement schedule. The Simply lasts up to 3 months per filter, the Filter King lasts up to 90 days, and the Filtrete is changed at least once every 12 months. The Filtrete Smart App can set 90-, 180- or 365-day reminders, which helps track the interval you choose.
FAQ
What actual size fits a 20x24x4 slot?
The Filter King is nominally 20 x 24 x 4 with an actual size of 19.38 x 23.38 x 3.75 inches. Measure the slot and compare it against the actual size, not just the nominal size.
How do MERV 8 and MERV 12 differ?
MERV rates particle capture, with a higher number meaning finer capture. The Simply and Filter King are MERV 8, while the Nordic Pure and Filtrete are MERV 12. Pick the rating that matches the capture level you want.
When should these filters be changed?
The Simply lasts up to 3 months per filter and the Filter King lasts up to 90 days. The Filtrete is changed at least once every 12 months, and its app sets 90-, 180- or 365-day reminders.
Do these filters fit Honeywell systems?
The Filtrete is designed to fit Honeywell and AprilAire Space-Gard media air cleaners. The Simply is not compatible with Honeywell, so check the fit notes for each pick before ordering.
