Furnace Filters
Best 20x20x4 Furnace Filter (2026): 5 Models Side by Side
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For a 20x20x4 furnace filter, the Simply leads as Best Overall: it pairs MERV 11 with a 6-pack at an actual size of 19.5 by 19.5 by 3.63 inches. The Filtrete runner-up pairs MERV 12 with MPR 1550 in a 2-pack of 12-month filters.
Starting out? See the main guide: Best Furnace Air Filters
Top picks at a glance
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Best OverallSimply 20x20x4 Air Filter9.8 View on Amazon -
Runner-UpFiltrete 20x20x4 Air Filter9.6 View on Amazon -
Also GreatNordic Pure 20x20x4 Pleated MERV 12 Air9.6 View on Amazon -
Also GreatAerostar Air Filter 20x20x4 MERV 11 AC9.6 View on Amazon -
9.2 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 20x20x4 Air Filter | MERV 11 | 6-pack | — | — |
| 2. Filtrete 20x20x4 Air Filter | MERV 12 | 2-pack | — | — |
| 3. Nordic Pure 20x20x4 Pleated MERV 12 Air | MERV 12 | 2-pack | — | — |
| 4. Aerostar Air Filter 20x20x4 MERV 11 AC | MERV 11 | 6-pack | — | — |
| 5. Honeywell FC100A1011-20" x 20" x 4" Pleated | MERV 11 | — | — | — |
Simply 20x20x4 Air Filter
It pairs MERV 11 with a 6-pack, a 19.5 by 19.5 by 3.63 actual size, and pleated media.
- MERV rating: MERV 11
- Pack size: 6-pack
Good for
- Buyers who want a 20x20x4 slot with MERV 11
- Buyers who want a 6-pack for repeat changes
Skip it if
- You want a filter larger than 20x20x4
- You want a MERV figure past 11
The pleated filters use a 24-point beverage board with hot-rolled steel wire mesh, and the particle size is 3.0 to 10.0 microns. The box holds 6 filters with an installation guide, and they give up to 3 months of filtration.
Filtrete 20x20x4 Air Filter
It pairs MERV 12 with MPR 1550, a 2-pack of 12-month pleated filters, and a Smart App reminder.
- MERV rating: MERV 12
- Pack size: 2-pack
Good for
- Buyers who want a 20x20x4 slot with MERV 12
- Buyers who want a 12-month filter
Skip it if
- You want a filter larger than 20x20x4
- You want a MERV figure past 12
The pleated filters use electrostatically charged media, and the 3-in-1 technology pulls in and traps particles while letting air flow through. The actual size is 19.88 by 19.88 by 4.31 inches, and the filters fit Honeywell brand media air cleaners. Change them at least once every 12 months, and the Smart App sets 90-, 180- or 365-day reminders.
Nordic Pure 20x20x4 Pleated MERV 12 Air
It pairs MERV 12 with a 2-pack, a 19.5 by 19.5 by 3.63 actual size, and pleated media.
- MERV rating: MERV 12
- Pack size: 2-pack
Good for
- Buyers who want a 20x20x4 slot with MERV 12
- Buyers who want a 2-pack for repeat changes
Skip it if
- You want a filter larger than 20x20x4
- You want a MERV figure past 12
The pleated filters use electrostatically charged synthetic media, and MERV 12 is equivalent to MPR 1500-1900. Measure your slot against the actual size before ordering.
Aerostar Air Filter 20x20x4 MERV 11 AC
It pairs MERV 11 with a 6-pack, a 19.50 by 19.50 by 3.75 actual size, and pleated media.
- MERV rating: MERV 11
- Pack size: 6-pack
Good for
- Buyers who want a 20x20x4 slot with MERV 11
- Buyers who want a 6-pack for repeat changes
Skip it if
- You want a filter larger than 20x20x4
- You want a MERV figure past 11
The pleated filters use 100% synthetic electrostatic media for high efficiency with low air flow resistance. The actual size is 19.50 by 19.50 by 3.75 inches, and the media is comparable to MPR 1000-1200 and FPR 7.
Honeywell FC100A1011-20" x 20" x 4" Pleated
It pairs MERV 11 with a 19.94 by 19.75 by 4.38 actual size and a reminder magnet.
- MERV rating: MERV 11
Good for
- Buyers who want a 20x20x4 slot with MERV 11
- Buyers who want a reminder magnet for changes
Skip it if
- You want a filter larger than 20x20x4
- You want a MERV figure past 11
The pleated filter measures 19.94 by 19.75 by 4.38 inches actual, and it fits air cleaners, air conditioners and furnaces. The bundle includes a reminder magnet, one per filter, so you know when you last changed the filter without opening the cabinet. Filters ship in individual clear plastic bags that can be reused for the old filter.
How to choose
Match the nominal size first
Start with the nominal size your slot takes. All five filters are 20x20x4 nominal, with actual sizes that vary: the Simply is 19.5 by 19.5 by 3.63, the Filtrete is 19.88 by 19.88 by 4.31, the Nordic Pure is 19.5 by 19.5 by 3.63, the Aerostar is 19.50 by 19.50 by 3.75, and the Honeywell is 19.94 by 19.75 by 4.38. Check the actual size against your slot before ordering.
Understand MERV and MPR
MERV and MPR are two separate scales, so compare MERV figures with MERV figures and MPR figures with MPR figures. The Simply, Aerostar and Honeywell are MERV 11, and the Filtrete and Nordic Pure are MERV 12. The Filtrete carries MPR 1550, and the Nordic Pure MERV 12 is equivalent to MPR 1500-1900. The Simply, Filtrete, Nordic Pure and Aerostar come in 6-pack, 2-pack, 2-pack and 6-pack sizes for repeat changes.
Plan changes and upkeep
Replacement timing is given in months or in reminders. The Simply gives up to 3 months of filtration, and the Filtrete changes at least once every 12 months with Smart App reminders at 90, 180 or 365 days. The Honeywell bundle includes a reminder magnet, one per filter, so you know when you last changed the filter. Check the replacement timing for your pick before you buy.
FAQ
What MERV figures do these filters have?
The Simply, Aerostar and Honeywell are MERV 11, and the Filtrete and Nordic Pure are MERV 12.
What size furnace filter do I need?
Check the nominal size for your slot first. All five are 20x20x4 nominal, with actual sizes from 19.5 by 19.5 by 3.63 to 19.94 by 19.75 by 4.38.
How do I know when to change the filter?
The Simply gives up to 3 months of filtration, and the Filtrete changes at least once every 12 months with Smart App reminders. The Honeywell reminder magnet shows when you last changed the filter.
Which filters come in a 6-pack?
The Simply and Aerostar come in 6-packs, while the Filtrete and Nordic Pure come in 2-packs.
