Furnace Filters
Best 18x24x4 Furnace Filter (2026): 3 Models Side by Side
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For an 18x24x4 furnace filter, the AIRx MERV 11 6-pack leads with pleated filtration, a moisture-resistant double-wall frame and a fit for 18x24x4 systems. The Glasfloss runner-up offers MERV 10 filtration in a 3-pack with a heavy-duty frame, while the Nordic Pure adds MERV 12 filtration in a 2-pack. All three share the 18x24x4 nominal size with different actual sizes, so check the exact size before you buy.
Starting out? See the main guide: Best Furnace Air Filters
Top picks at a glance
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Best OverallAIRx Filters 18x24x4 Furnace AC Filter MERV9.8 View on Amazon -
9.3 View on Amazon -
Also GreatNordic Pure 18x24x4 Pleated MERV 12 Air9.2 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. AIRx Filters 18x24x4 Furnace AC Filter MERV | MERV 11 | 6-pack | — | — |
| 2. Glasfloss ZL 18x24x4 MERV 10 Pleated Air | MERV 10 | 3-pack | — | — |
| 3. Nordic Pure 18x24x4 Pleated MERV 12 Air | MERV 12 | 2-pack | — | — |
AIRx Filters 18x24x4 Furnace AC Filter MERV
It pairs MERV 11 pleated filtration with a 6-pack, a moisture-resistant double-wall frame and an 18x24x4 fit.
- MERV rating: MERV 11
- Pack size: 6-pack, the most here
Good for
- Buyers who want MERV 11 filtration in a 6-pack
- Buyers who want a moisture-resistant double-wall frame
Skip it if
- You want a MERV rating above 11
- You want a pack smaller than 6 filters
The moisture-resistant double-wall beverage board frame stands up to 180 degrees, and the nominal size is 18x24x4 with an actual size of 17.50 x 23.50 x 3.75 inches. Replace the filter every 60 to 90 days, and the box holds 6 filters made in the USA.
Glasfloss ZL 18x24x4 MERV 10 Pleated Air
It pairs MERV 10 pleated filtration with a 3-pack, an exact 17-1/2 x 23-1/2 x 3-3/4 size and a heavy-duty frame.
- MERV rating: MERV 10
- Pack size: 3-pack
Good for
- Buyers who want MERV 10 filtration in a 3-pack
- Buyers who want a heavy-duty frame made in USA
Skip it if
- You want a MERV rating above 10
- You want a pack smaller than 3 filters
The pleated filter carries a MERV 10 rating with an exact size of 17-1/2 x 23-1/2 x 3-3/4 and a nominal size of 18x24x4. Airflow is comparable to a MERV 8, and the durable heavy-duty frame is made in the USA for residential and commercial use. Change the filter at least every 3 months, and check the actual size before buying, since it does not replace 5-inch or 4-3/8-inch depth filters.
Nordic Pure 18x24x4 Pleated MERV 12 Air
It pairs MERV 12 pleated filtration with a 2-pack and an actual size of 17 1/2 x 23 3/8 x 3 5/8.
- MERV rating: MERV 12
- Pack size: 2-pack
Good for
- Buyers who want MERV 12 filtration in a 2-pack
- Buyers who want electrostatically charged synthetic pleated media
Skip it if
- You want a MERV rating above 12
- You want a pack smaller than 2 filters
The pleated filter carries a MERV 12 rating, equivalent to MPR 1500-1900, with a nominal size of 18 x 24 x 4 and an actual size of 17 1/2 x 23 3/8 x 3 5/8. Measure your filter for the exact size and compare it to the actual size for a proper fit. The electrostatically charged synthetic pleated media is made in the USA, and the box holds 2 filters for residential systems.
How to choose
Compare MERV ratings first
MERV rating is the clear split in this list: the Nordic Pure carries MERV 12, the AIRx carries MERV 11 and the Glasfloss carries MERV 10. Pack size runs the other way: 6 filters for the AIRx, 3 for the Glasfloss and 2 for the Nordic Pure, so weigh rating against your filter-change schedule.
Check actual size, not nominal
All three filters share the 18x24x4 nominal size, but their actual sizes differ: the AIRx measures 17.50 x 23.50 x 3.75 inches, the Glasfloss measures 17-1/2 x 23-1/2 x 3-3/4, and the Nordic Pure measures 17 1/2 x 23 3/8 x 3 5/8. Measure your air filter and compare it to the actual size before you buy, since a nominal match alone does not guarantee a fit. The Glasfloss does not replace 5-inch or 4-3/8-inch depth filters, so check depth as well as length and width.
Frames, airflow and replacement
Frame and airflow shape everyday use: the AIRx uses a moisture-resistant double-wall beverage board frame that stands up to 180 degrees, the Glasfloss uses a durable heavy-duty frame, and the AIRx pleated design gives a larger surface area without restricted airflow. Keep a spare pack on hand so a change is never delayed.
FAQ
What MERV rating does each filter carry?
The Nordic Pure carries MERV 12, the AIRx carries MERV 11 and the Glasfloss carries MERV 10, all in the 18x24x4 nominal size.
How many filters come in each pack?
The AIRx comes as a 6-pack, the Glasfloss as a 3-pack and the Nordic Pure as a 2-pack, all made in the USA.
What actual size is each filter?
The AIRx measures 17.50 x 23.50 x 3.75 inches, the Glasfloss measures 17-1/2 x 23-1/2 x 3-3/4, and the Nordic Pure measures 17 1/2 x 23 3/8 x 3 5/8.
When should I replace the AIRx and Glasfloss filters?
Replace the AIRx every 60 to 90 days and the Glasfloss at least every 3 months.
