Representative image — you’ll receive the exact size you select. Actual dimensions are in the specs.
Smith Filter Corporation
Custom Size Bonded “A” Thin Aluminum Washable Permanent Filter
Enter your exact filter size to the nearest 1/8″. Fractional (18-1/4) or decimal (18.25) both accepted.
Standard size range: 6" x 6" minimum to 25" x 30" maximum. Need help measuring? See our how to measure guide.
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Product details
This is our custom-size Bonded “A” Aluminum Washable Permanent Filter — built to your exact dimensions by Smith Filter Corporation. It is the thin member of the washable aluminum family: where the Mech 8, Thrift Aire and Electrostatic panels start at 1/2″, the Bonded “A” is made as shallow as 1/8″, so it drops into openings that will not take a conventional filter at all.
Why this filter exists
Plenty of equipment has a filter slot measured in fractions of an inch — a ceiling vent fan, a microwave grease slot, a wall heater intake, an equipment cabinet louver. Those openings normally get whatever thin pad the OEM sold once and never stocked again. The Bonded “A” replaces that pad permanently: same shallow depth, aluminum frame, and you wash it instead of buying it again.
Choose your depth
Depth is the whole point of this filter. Six depths are made to order:
- 1/8″ — the shallowest slots: vent fan grilles, louvered covers, tight OEM tracks
- 1/4″ — the most common thin-pad replacement depth
- 5/16″ and 3/8″ — odd OEM slots that a 1/4″ rattles in and a 1/2″ will not enter
- 7/16″ — near-half-inch openings with no clearance to spare
- 1/2″ — the deepest Bonded “A”, and the crossover point with our standard washable panels
Measure the slot, not the old pad, if the old pad has been compressed. If you are between two depths, take the shallower one — a filter that will not seat is worse than one with a little play.
Where it gets used
- Ceiling and bathroom vent fans
- Kitchen and commercial exhaust hoods
- Microwave grease-filter slots
- Wall heaters and through-wall units
- Electronic equipment and computer-environment cabinets
- Room air cleaners and OEM appliance intakes
Construction
- Media — bonded aluminum: layers of aluminum slit and expanded into mesh of differing densities, then bonded into a solid pad of tiny baffles
- Frame — sheet aluminum 3003-H14, .020 thickness, roll formed and riveted at one corner
- Resistance when clean — .04″ w.g. at 350 FPM
- Average arrestance — 71.5%
- Dust holding capacity — 90.8 grams per foot (204 grams per 2.25 sq ft on a 20x20)
- Maximum temperature — 225°F
- Rust resistant, washable, reusable — no replacement cycle
This is a low-resistance equipment-protection filter, not an air-quality filter. It is built to stop lint, hair, grease-borne debris and large dust before they reach a fan wheel, coil or heat exchanger, while costing the airflow almost nothing. If you need particulate capture, pair it with a pleated filter downstream rather than replacing it.
Size limits — read this before ordering
The Bonded “A” is made to order, and its limit is area, not a fixed size chart:
- Maximum 550 square inches (length × width)
- Maximum width 24″
- Sized to the nearest 1/8″
The size fields on this page accept up to 23″ × 23″, which is inside the 550 sq. in. limit in every combination. If you need a panel that uses the full 24″ width, or a long-and-narrow shape that stays under 550 sq. in. but exceeds 23″ on one side, contact us and we will place it for you. Anything larger than 550 sq. in. has to be split into multiple panels — we will lay that out with you.
How to order
Measure your opening to the nearest 1/8″ and enter length × width above, then pick your depth. If you are replacing an existing filter, measure the filter itself rather than the housing. A quick photo of the old pad or the opening lets us confirm before production — send it over if you are unsure. Our Filter Fit Guarantee means if you measure wrong, we remake the filter at no additional cost.
Care and maintenance
- Rinse every 30–60 days with warm water from the downstream side
- Mild dish detergent for grease loading — kitchen and hood applications will need it
- Let it air-dry completely before reinstalling
- Note the airflow-direction arrow before removing
Also worth considering
Need 1/2″ or deeper in the same washable aluminum family? See our Custom Size Mech 8, Custom Size Thrift Aire, and Custom Size Electrostatic permanent filters, which run 1/2″ through 4″ and up to 25″ × 30″.
Questions on fit, quantity, or a commercial quote?
Running a kitchen, a facility, or a fleet of the same unit? Get in touch — we handle facilities and commercial orders daily, and repeat thin-pad sizes are exactly the kind of order we can price better than a distributor.
Commercial & facilities
Buying filters for a building?
Volume pricing on any size or MERV, plus recurring delivery schedules. We handle facilities and commercial orders daily and can usually match or beat distributor pricing.
When your slot doesn't match a standard size, custom is the right fix.
Not every HVAC system was built around today's standard filter sizes. Custom filters close the gap.
You set the dimensions
Enter your exact size in the custom-size field above to the nearest 1/8″ on length, width, and depth. Size range: 6" x 6" minimum to 25" x 30" maximum.
Need a size larger than 25" x 30"? Request a quote.
Built to your specification
Production begins after you order. Each filter is built to the dimensions you specified — non-standard sizes don't sit on shelves.
Typical delivery 6 to 10 business days. See current timing.
Closes the bypass gap
When a filter doesn't fit its slot, air takes the path of least resistance — around the filter instead of through it. A filter sized to your slot closes that gap, so it captures what it's rated to capture.
More on filter bypass further down this page.
American business partnerships with the names commercial HVAC runs on.
Custom filter retailers have multiplied over the past decade, and most don't build their own filters. They source generic stock from overseas, relabel it, and cut it in a warehouse. That's not what we do. When you order a custom filter from us, it's built to your specifications by one of the established names in indoor air filtration — the same manufacturers commercial HVAC contractors, schools, clinics, and government facilities have specified for decades. RTF operates the distribution front-end for the companies that build these filters, through long-standing business partnerships that let your custom order ship direct from the plant that built it.
One of North America's two largest names in industrial air filtration. Custom sizes built on the same production lines that supply commercial HVAC contractors nationwide. Pleated and fiberglass construction.
One of North America's two largest names in industrial air filtration. Four U.S. manufacturing locations. Known for AHU-rated custom filters used in institutional and facility installations.
Manufacturer of our washable electrostatic custom filters. Aluminum-frame construction built to your dimensions, designed for permanent installation with periodic cleaning instead of replacement.
Individually sealed filters — each packaged in its own protective bag for the cleanest installation experience. Custom sizes produced directly from their production line. Good choice for allergy-conscious households and facilities wanting reduced packaging contamination.
Our house line, produced to RTF specifications by established manufacturers. Built to commercial filter standards and priced to give customers a house-brand option without compromising build quality.
Shipped direct from the manufacturing plant.
Most custom filter retailers route your order through a warehouse or cutting shop before shipping. We don't. The plant that built your filter ships directly to you — fewer hands on the box, shorter lead time, lower cost. Industrial-grade filter, no industrial-distribution markup.
No secretly imported house-brands. No “manufactured to order” claims that dissolve under scrutiny. Real American business partnerships, real industrial-grade filters, shipped direct from the plants that built them.
Custom filters exist because not every HVAC system uses standard sizes.
HVAC systems installed before the industry standardized on today's common sizes often have non-standard slot dimensions. Legacy equipment isn't broken — the catalog just hasn't caught up to what's already installed.
Rooftop package units and commercial air handlers from Carrier, Trane, Lennox, York, and others often use manufacturer-specific slot dimensions that don't match residential retail sizes. Custom sizing matches the OEM spec.
Homes built before roughly 1990 often have return grilles with dimensions like 16-1/2″ or 20-3/4″ that don't match a big-box catalog. Regional manufacturers standardized differently before the industry consolidated.
Some air handlers were designed around a specific filter size the OEM produced. When those OEM filter lines get discontinued, the equipment still needs filters — custom sizing keeps older systems running on spec.
Institutional properties often have mixed HVAC inventory across buildings — some standard, some not. Custom filters cover the non-standard portion so the whole property can standardize on one supplier.
Filters trimmed from a larger size, stacked, or gap-filled with foam are signs your slot needs a custom spec. A filter in the actual slot dimensions stops the workaround cycle for good.
Your system was designed around its filter slot. Forcing a standard size in doesn't work.
When an HVAC system has a non-standard filter opening, the most common reaction is to force the closest standard size to work. Common workarounds customers try:
Trim a larger filter down. Cutting the frame breaks the bond between the frame and the media. The filter fits dimensionally, but media face area shrinks and the frame no longer seals the slot edges. Trimmed filters leak worse than no filter at all in some spots — air channels around the cut.
Stack smaller filters. Two filters back-to-back doubles the pressure drop, chokes airflow, and shortens blower life. Gaps between stacked filters also create turbulence, which defeats the capture rate.
Force an oversized filter in. Pushing a filter into a tight slot warps the frame and crushes the media. Warped filters create turbulence where there should be laminar flow; crushed media loses rated efficiency. The filter is there, but filtering at a fraction of its MERV spec.
Gap-fill with foam or weatherstripping. Foam compresses unevenly and shifts during operation, so the seal there at installation isn't there six months later. Worse, foam itself collects dust and mold, which gets pulled into the system every time the blower runs.
The workaround tax adds up. Unfiltered air bypassing a poorly-fit filter accelerates dust buildup on coils and blower wheels — reducing heat transfer, raising energy costs, and shortening component life. Over a few years, the service calls and early component replacements cost more than years of correctly-sized filters. A custom filter built to your slot isn't a premium — it's the configuration your system was designed for.
Custom filters for properties, portfolios, and standing orders.
Custom filters aren't just for one-off replacements. Schools, clinics, multifamily properties, and property management companies routinely order custom sizes for their legacy and non-standard HVAC inventory. We'll consolidate the spec across mixed-size portfolios, quote volume pricing, set up net-terms or tax-exempt accounts, and schedule standing delivery matched to your change-out cycle.
For larger portfolios, we coordinate consolidated freight direct from the plant.
What customers say about Custom Size Bonded “A” Thin Aluminum Washable Permanent Filter
Common questions about ordering a custom filter.
Built on the back of 50 years of HVAC filtration experience.
Enter your exact dimensions in the custom-size field above, or reach out if you'd like help sizing a slot or quoting a commercial order.