Furnace Filters
Best 18x24 AC 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.
For an 18x24 slot, the Simply 18x24x1 leads this list: it pairs a MERV 8 rating with a 6-pack and an actual size of 17.75 x 23.75 x 0.75 inches. The other picks cover MERV 5 through MERV 12 in the same nominal size, so the choice comes down to rating and pack size.
Starting out? See the main guide: Best Furnace Air Filters
Top picks at a glance
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Best OverallSimply 18x24x1 Air Filter9.8 View on Amazon -
Runner-UpFilter King 18x24x1 Air Filter MERV9.7 View on Amazon -
Also GreatFiltrete 18x24x1 Air Filter9.5 View on Amazon -
Also GreatNordic Pure 18x24x19.5 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 18x24x1 Air Filter | MERV 8 | 6-pack | — | — |
| 2. Filter King 18x24x1 Air Filter MERV | MERV 8 | 6-pack | — | — |
| 3. Filtrete 18x24x1 Air Filter | MERV 5 | — | — | — |
| 4. Nordic Pure 18x24x1 | MERV 12 | 6-pack | — | — |
| 5. AIRx Filters 18x24x1 Furnace AC Filter MERV | MERV 11 | — | — | — |
Simply 18x24x1 Air Filter
A MERV 8 pleated filter in a 6-pack, with an actual size of 17.75 x 23.75 x 0.75 inches for 18x24x1 slots.
- MERV rating: MERV 8
- Pack size: 6-pack
Good for
- Buyers who want a 6-pack of MERV 8 filters
- Owners of 18x24x1 slots who want pleated filters
Skip it if
- You want a MERV rating above 8
- You want fewer than 6 filters at a time
It traps 90% of airborne particles and lasts up to 3 months per filter. The pleated design fits central units or return grilles, following the airflow arrows on the frame. It is made in the USA from American components, including recycled materials.
Filter King 18x24x1 Air Filter MERV
A MERV 8 pleated filter in a 6-pack, with an actual size of 17.5 x 23.5 x .75 inches.
- MERV rating: MERV 8
- Pack size: 6-pack
Good for
- Owners of 18x24x1 slots who change filters every 30 to 90 days
- Buyers who want a pleated 6-pack for air conditioners
Skip it if
- You want a MERV rating above 8
- You want a filter that lasts past 90 days
The pleated design captures particles without restricting airflow, and each filter lasts up to 90 days. Installation is open, slide and close, for a simple swap in the filter slot.
Filtrete 18x24x1 Air Filter
A MERV 5 filter with a 300 MPR rating, in a 6-pack for standard HVAC systems.
- MERV rating: MERV 5
Good for
- Buyers who want basic dust and lint filtration
- Owners of standard HVAC systems using 18x24x1 filters
Skip it if
- You want a MERV rating above 5
- You want a 4-pack instead of a 6-pack
It uses Filtrete 3-in-1 technology to pull in and trap particles, with an actual size of 17.81 x 23.81 x 0.81 inches. Change it at least once every 90 days, and a smart app sets 30-, 60- or 90-day reminders. It carries a limited warranty.
Nordic Pure 18x24x1
A MERV 12 pleated filter in a 6-pack, equivalent to MPR 1500-1900.
- MERV rating: MERV 12
- Pack size: 6-pack
Good for
- Buyers who want a MERV 12 filter
- Owners of 18x24x1 slots who want high efficiency filtration
Skip it if
- You want a MERV rating below 12
- You want fewer than 6 filters at a time
The nominal size is 18 x 24 x 1, with an actual size of 17.5 x 23.5 x 0.75 inches. Measure your old filter and compare it with the actual size for a proper fit. It is made in the USA.
AIRx Filters 18x24x1 Furnace AC Filter MERV
A MERV 11 pleated filter in a 4-pack, with a moisture-resistant double-wall frame.
- MERV rating: MERV 11
Good for
- Buyers who want a MERV 11 filter
- Owners of 18x24x1 slots who want a 4-pack
Skip it if
- You want a MERV rating above 11
- You want a 6-pack instead of a 4-pack
It captures 85% of particles with a pleated design for airflow, at a MERV 11 rating. The frame withstands temperatures up to 180°F, and the actual size is 17.50 x 23.50 x 0.75 inches. Replace it every 60-90 days.
How to choose
Match the nominal size to the slot
Nominal size is the labeled size, and actual size runs slightly smaller. The picks here are all labeled 18x24x1, with actual sizes from 17.5 x 23.5 x 0.75 inches to 17.81 x 23.81 x 0.81 inches. Measure your old filter and compare the actual size before ordering, so the new filter fits the slot.
Compare MERV ratings, not pack counts
MERV rates how finely a filter captures particles, so a higher number means finer capture. This list runs from MERV 5 on the Filtrete to MERV 12 on the Nordic Pure, with MERV 8 and MERV 11 picks between them. Pack count only sets how many filters arrive at once, so compare the rating first and the pack size second.
Set a replacement schedule
Change filters on schedule to keep them working as intended, so pick an interval you will keep. The Simply lasts up to 3 months. The Filter King lasts up to 90 days. The Filtrete needs a change at least once every 90 days, with app reminders at 30, 60 or 90 days. The AIRx needs a change every 60-90 days. Write the install date on the frame edge as a reminder.
FAQ
What size filter fits an 18x24 slot?
Buy a filter labeled 18x24x1, then check the actual size against your old filter. The picks here run from 17.5 x 23.5 x 0.75 inches to 17.81 x 23.81 x 0.81 inches.
When should I replace an 18x24 filter?
It depends on the pick. The Simply lasts up to 3 months, the Filter King up to 90 days, the Filtrete needs a change at least once every 90 days, and the AIRx every 60-90 days.
What does MERV mean on an air filter?
MERV rates how finely a filter captures particles, so a higher number means finer capture. This list runs from MERV 5 to MERV 12.
Do these filters come in multi-packs?
The Simply, Filter King, Filtrete and Nordic Pure come in 6-packs, and the AIRx comes in a 4-pack. Check the pack size before ordering so you know how many filters arrive.
