Furnace Filters
Best 18x20 Furnace Filter (2026): 5 Models Side by Side
As an Amazon Associate I earn from qualifying purchases. Specs below come from each product's Amazon listing; we do not test products in person.
The Simply 18x20x1 filter leads this list with a MERV 13 rating in a 6-pack. The choice turns on MERV rating, pack size and change interval, so check each pick's nominal size against its actual size before ordering.
Starting out? See the main guide: Best Furnace Air Filters
Top picks at a glance
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Best OverallSimply 18x20x1 Air Filter9.8 View on Amazon -
9.8 View on Amazon -
Also GreatFilter King 18x20x1 Air Filter MERV9.3 View on Amazon -
Also GreatClorox 18x20x1 Air Filter9.3 View on Amazon -
Also GreatFiltrete 18x20x1 Air Filter9.2 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 18x20x1 Air Filter | MERV 13 | 6-pack | — | — |
| 2. Aerostar Air Filter 18x20x1 MERV 13 AC | MERV 13 | 6-pack | — | — |
| 3. Filter King 18x20x1 Air Filter MERV | MERV 11 | 4-pack | — | — |
| 4. Clorox 18x20x1 Air Filter | MERV 13 | 4-pack | — | — |
| 5. Filtrete 18x20x1 Air Filter | MERV 13 | — | — | — |
Simply 18x20x1 Air Filter
A MERV 13 pleated filter in a 6-pack with an actual size of 17.75 by 19.75 by 0.75 inches and airflow arrows for fitting.
- MERV rating: MERV 13
- Pack size: 6-pack
Good for
- Buyers who want a 6-pack of MERV 13 filters
- Owners replacing filters in central units or return grilles
Skip it if
- You want a MERV 11 filter
- You want a 4-pack
It measures 18 by 20 by 1 inch nominal, with an actual size of 17.75 by 19.75 by 0.75 inches. The pleated design carries airflow arrows for the filter slot, and the maker gives up to 3 months of filtration. It is made in the USA from American components, including recycled materials.
Aerostar Air Filter 18x20x1 MERV 13 AC
A MERV 13 filter in a 6-pack with synthetic electrostatic media and a 60 to 90 day change interval.
- MERV rating: MERV 13
- Pack size: 6-pack
Good for
- Buyers who want synthetic electrostatic media
- Owners who change filters every 60 to 90 days
Skip it if
- You want a MERV 11 filter
- You want a 4-pack
It measures 18 by 20 by 1 inch nominal, with an actual size of 17.50 by 19.50 by 0.75 inches. The media is 100% synthetic electrostatic media for high efficiency with low air flow resistance. Change frequency rises to 30 days during peak summer and winter months.
Filter King 18x20x1 Air Filter MERV
A MERV 11 filter in a 4-pack with a pleated design and a 30 to 90 day change interval.
- MERV rating: MERV 11
- Pack size: 4-pack
Good for
- Buyers who want a 4-pack of MERV 11 filters
- Owners who change filters every 30 to 90 days
Skip it if
- You want a MERV 13 filter
- You want a 6-pack
It measures 18 by 20 by 1 inch nominal, with an actual size of 17.5 by 19.5 by .75 inches. The pleated design captures more particles, and the maker gives up to 90 days before replacement. Installation is open, slide and close.
Clorox 18x20x1 Air Filter
A MERV 13 pleated filter in a 4-pack with synthetic electrostatically charged media and wire-backed support.
- MERV rating: MERV 13
- Pack size: 4-pack
Good for
- Buyers who want a 4-pack of MERV 13 filters
- Owners who want airflow direction marked on the frame
Skip it if
- You want a MERV 11 filter
- You want a 6-pack
It is a MERV 13 pleated filter with synthetic electrostatically charged media for balanced airflow and filtration efficiency. Beverage board framing and wire-backed media support the structure for long-term performance. The pleated design gives up to 90 days of filtration under normal operating conditions.
Filtrete 18x20x1 Air Filter
A MERV 13 filter with MPR 1900, 3-in-1 technology and a 90-day change interval in a 2-pack.
- MERV rating: MERV 13
Good for
- Buyers who want a 2-pack of MERV 13 filters
- Buyers who want 30-, 60- or 90-day change reminders
Skip it if
- You want a MERV 11 filter
- You want a 4-pack
It is a 3-month pleated 1-inch filter with Filtrete 3-in-1 technology to pull in and trap unwanted particles. Microparticles are 0.3 to 1.0 microns in size. The Filtrete Smart App sets 30-, 60- or 90-day reminders to change the filter.
How to choose
Check nominal size against actual size
An 18x20x1 filter is a nominal size, and the actual size runs smaller. The Simply measures 17.75 by 19.75 by 0.75 inches, the Aerostar measures 17.50 by 19.50 by 0.75 inches, and the Filter King measures 17.5 by 19.5 by 0.75 inches. Measure the old filter or the slot before ordering, and match the actual size rather than the nominal size alone.
Compare MERV rating and pack size
MERV rating is the filter's rating for particle capture, and pack size decides how many filters one order holds. The Simply, the Aerostar, the Clorox and the Filtrete carry MERV 13, while the Filter King carries MERV 11. The Simply and the Aerostar come in 6-packs, the Filter King and the Clorox come in 4-packs, and the Filtrete comes in a 2-pack.
Set a change interval and keep spares
Change intervals in this list run from 30 days to 90 days, so pick a rhythm that matches the maker's guidance for each filter. The Simply gives up to 3 months, the Aerostar gives 60 to 90 days with 30 days in peak summer and winter, the Filter King and the Clorox give up to 90 days, and the Filtrete asks for a change at least once every 90 days. A multi-pack keeps the next filter on hand when the interval ends.
FAQ
What does MERV 13 mean for a furnace filter?
MERV is the filter's rating scale, and a higher number rates the filter for smaller particles. The Simply, the Aerostar, the Clorox and the Filtrete carry MERV 13, while the Filter King carries MERV 11.
When should I change an 18x20 furnace filter?
The Simply gives up to 3 months, the Aerostar gives 60 to 90 days with 30 days in peak summer and winter, and the Filter King and the Clorox give up to 90 days. The Filtrete asks for a change at least once every 90 days.
Do I need the nominal size or the actual size?
Use the actual size. The Simply measures 17.75 by 19.75 by 0.75 inches, the Aerostar measures 17.50 by 19.50 by 0.75 inches, and the Filter King measures 17.5 by 19.5 by 0.75 inches.
What is the difference between a 6-pack and a 2-pack?
Pack size is how many filters one order holds. The Simply and the Aerostar come in 6-packs, the Filter King and the Clorox come in 4-packs, and the Filtrete comes in a 2-pack.
