The best cheap A/C filter depends on your unit: washable foam is suited to many window air conditioners, while disposable pleated filters are made for compatible central HVAC systems. Frost King and Duck offer cut-to-fit foam options; Amazon Basics provides budget-friendly six-packs in several common sizes. Check your existing filter’s dimensions and your equipment manual before choosing, since a filter that does not fit can leave gaps or restrict airflow.
| Product | Best For | Type |
|---|---|---|
| Frost King 15 x 24-inch Foam | Washable replacement foam | Cut-to-fit |
| Duck 24 x 15-inch Foam | Reusable, customizable foam | Cut-to-fit |
| Amazon Basics 14 x 20 x 1 | Six-pack value in this size | MERV 8 pleated |
| Amazon Basics 16 x 20 x 1 | Six-pack value in this size | MERV 8 pleated |
| Amazon Basics 20 x 25 x 1 | Six-pack value in this size | MERV 8 pleated |
Frost King Washable Foam Filter
Frost King’s open-cell foam filter is a practical choice for buyers seeking a reusable filter for an air conditioner. The listed product is a washable foam filter, with dimensions described as 15 by 24 inches and a thickness around one-quarter inch. Its foam format can be trimmed to fit a compatible filter opening.
Best for: People replacing foam in an air conditioner who want a washable option rather than a disposable pleated HVAC filter. It was selected because its listed dimensions and reusable foam construction suit a simple replacement need.
Limitation: Confirm the thickness and opening dimensions before purchase; foam media is not interchangeable with every central HVAC filter.
Duck Cut-To-Fit Foam Filter
This Duck Brand replacement filter is a 24-by-15-inch polyurethane foam sheet. The listed features say it helps eliminate dust and pollen, can be washed and reused, and can be cut down to size. That flexibility makes it useful when an air conditioner needs foam media in a nonstandard opening.
Best for: Buyers who need customizable, reusable foam for a compatible air conditioner. Choose this if cutting a sheet to fit is more useful than buying a rigid, pre-sized pleated filter.
Limitation: Cutting is required when the filter opening is smaller than the sheet, and the product is foam—not a standard one-inch central-system filter.
Amazon Basics 14 x 20 MERV 8 Filters
This six-pack is designed for systems that use a nominal 14-by-20-by-1-inch filter. Its actual dimensions are 13.75 by 19.75 by 0.75 inches. The MERV 8 electrostatic media is described as capturing lint, dust, and pollen. A beverage-board frame and wire mesh support complete the construction.
Best for: Households whose equipment calls for this nominal size and buyers who want multiple replacement filters on hand. It was selected for its stated particle-capture features and multipack format.
Limitation: The actual dimensions are smaller than the nominal size. Verify the measurements and filter slot requirements before ordering.
Amazon Basics 16 x 20 MERV 8 Filters
This Amazon Basics six-pack is made for a nominal 16-by-20-by-1-inch filter opening. Each filter’s actual size is 15.75 by 19.75 by 0.75 inches. The MERV 8 electrostatic filter is listed for capturing household dust, lint, and pollen, and its supported frame is designed for durability.
Best for: Buyers whose HVAC system specifies this size and who prefer to stock several replacements at once. Compared with the 14-by-20 option, it suits a wider filter slot; the MERV rating and listed construction are otherwise similar.
Limitation: It is not a universal size. Do not choose it based on nominal dimensions alone if your equipment requires another size or thickness.
Amazon Basics 20 x 25 MERV 8 Filters
This six-pack targets systems that call for a nominal 20-by-25-by-1-inch filter. The stated actual size is 19.75 by 24.75 by 0.75 inches. Like the other selected Amazon Basics options, it has MERV 8 electrostatic media intended to capture dust, lint, and pollen, plus a beverage-board frame and wire mesh support.
Best for: Homes with a compatible 20-by-25 filter slot where a multipack helps keep replacement filters available. It offers the same stated MERV rating as the 14-by-20 and 16-by-20 choices, in a larger nominal size.
Limitation: The listed actual dimensions differ from the nominal size, so measure the existing filter or consult the unit documentation.
Buying Guide: How To Choose A Cheap A/C Filter
Does your system use foam or a one-inch filter?
Start by identifying the filter type. Window air conditioners may use foam inserts, while central air conditioners and furnaces commonly use a specified replaceable filter. The products above are not interchangeable: foam sheets are washable and cut-to-fit, while pleated filters are sized for particular HVAC filter slots.
Which dimensions should you check?
Read the size on the current filter and compare it with the product’s actual measurements. Nominal sizes are rounded labels; the listed Amazon Basics filters have actual dimensions smaller than their nominal measurements. Also confirm thickness and airflow direction requirements in the equipment manual where applicable.
Is a higher MERV rating always better?
These selected pleated filters are MERV 8. MERV ratings describe particle filtration, but a filter must also be suitable for the equipment. Follow the manufacturer’s guidance instead of selecting a rating solely because it is higher; an unsuitable filter may affect airflow.
How can you compare ongoing value?
Compare how many filters are included, whether the media is reusable, and how often your equipment instructions call for replacement or cleaning. A washable foam sheet may reduce disposable-filter purchases, while a six-pack provides several replacements but is not reusable. Consider the right size first, then compare maintenance needs.
Frequently Asked Questions
Can I use a foam filter in a central HVAC system?
Only if the equipment is designed for that filter type and the foam meets the specified size and airflow requirements. Check the system manual before substituting foam for a pleated filter.
Are these filters compatible with every air conditioner?
No. Compatibility depends on the filter slot or opening, required dimensions, and filter type. Match the product to the unit’s requirements before buying.
What does MERV 8 mean on these filters?
MERV 8 is the listed filtration rating for the Amazon Basics pleated options. Their product details say they capture household lint, dust, and pollen.
Can washable foam filters be reused?
The Frost King and Duck foam products are described as washable or reusable. Follow the product instructions for cleaning and ensure the filter is ready for use before reinstalling it.