Representative image — you’ll receive the exact size you select. Actual dimensions are in the specs.

Smith Filter Corporation

Custom Size Electrostatic Aluminum Washable Permanent Filter

    Enter your exact filter size to the nearest 1/8″. Fractional (18-1/4) or decimal (18.25) both accepted.

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    Standard size range: 6" x 6" minimum to 25" x 30" maximum. Need help measuring? See our how to measure guide.

    $179.99
    $179.99 $71.99
    Shipping calculated at checkout.
    • Free shipping over $50
    • 30-day returns
    • Secure checkout
    • US-based expert support
    Estimated delivery: Aug 28 – Sep 3
    Made to specification — see current production schedule for live timing.
    About the filter image
    Images are representative across sizes. You'll receive the exact size you select above — actual dimensions are listed in the product specs.
    Not sure which size? How to measure · Filter Fit Guarantee

    Product details

    This is our custom-size Electrostatic Aluminum Washable Permanent Filter — built to your exact dimensions in any size. Same rust-resistant aluminum construction as our stock-size washable filters, same indefinite service life with basic monthly care; just sized to fit non-standard filter openings.

    When a custom washable makes sense

    • Non-standard filter openings where stock sizes leave bypass gaps
    • Rental properties where tenants forget to change filters
    • Commercial facilities wanting to eliminate the recurring filter spend
    • Off-grid, remote, or retreat properties with limited filter supply chain

    What you get

    • Rust-resistant aluminum frame — holds up to repeated washing
    • Reusable filter system — wash, dry, return to service
    • MERV 1-4 rating — equipment protection with maximum airflow
    • Typical service life 5–10+ years with basic monthly care
    • 1/8 inch sizing tolerance

    Understanding the MERV 1–4 rating

    Fiberglass media is rated MERV 1 when clean and builds up to MERV 4 as dust loads onto the fibers. That's not inconsistency — it's how spun-glass media works. A fresh filter lets the most air through while still blocking larger debris; as dust collects, the media becomes more efficient at catching finer particles. The goal of a MERV 1–4 filter isn't air quality — it's equipment protection with maximum airflow. It keeps lint, hair, and large dust out of your coil and blower, which is exactly what older systems, high-airflow applications, and pre-filter duty need.

    How to order

    Measure your filter opening to the nearest 1/8 inch. If replacing an existing filter, measure the filter itself, not the housing. Contact us if you're unsure — a quick photo of the existing filter or housing lets us confirm before production. Our Filter Fit Guarantee means if you measure wrong, we'll 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 heavy loading
    • Let air-dry completely before reinstalling
    • Note the airflow-direction arrow before removing

    Also worth considering

    Shopping on price? Our house brand PrimeShield MAX Airflow (MERV 1–4) covers the same efficiency tier across common residential and commercial sizes and is usually the better value. Choose this branded option when your equipment spec sheet or facilities team calls for it specifically.

    Questions on fit, quantity, or a commercial quote?

    Need a size that isn't listed, a different pack count, or a quote for a commercial order? Get in touch — we handle facilities and commercial orders daily and can usually match or beat distributor pricing.

    Custom Size Electrostatic Aluminum Washable Permanent Filter

    $179.99
    Filter Fit Guarantee
    If it doesn't fit, we rebuild it.
    Made to Specification
    1/8″ precision, 6" x 6" to 25" x 30".
    Ships Direct from Plant
    Free shipping on orders $50+ (lower 48).
    Verified Reviews
    Why a Custom Filter

    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.

    Built by Leaders in Indoor Air Filtration

    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.

    AAF Flanders
    Industrial Air Filtration

    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.

    Koch Filter
    Industrial Air Filtration

    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.

    Smith Filter Corporation
    Washable Electrostatic

    Manufacturer of our washable electrostatic custom filters. Aluminum-frame construction built to your dimensions, designed for permanent installation with periodic cleaning instead of replacement.

    NaturalAire
    Individually Sealed Filters

    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.

    PrimeShield
    RTF House Brand

    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.

    Direct From the Plant

    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.

    Who Orders These

    Custom filters exist because not every HVAC system uses standard sizes.

    Legacy air handlers

    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.

    Commercial rooftop units

    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.

    Older homes

    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.

    Built-in filter housings

    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.

    Schools, clinics, and multifamily

    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.

    Customers replacing a workaround

    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.

    Why Custom Exists

    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.

    Commercial & Bulk Custom Orders

    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.

    For facility buyers
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    Volume pricing on recurring custom orders
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    Net terms for established accounts
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    Tax-exempt setup for schools and government
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    Standing orders on your change-out cycle
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    Spec consolidation across mixed sizes
    Customer Reviews

    What customers say about Custom Size Electrostatic Aluminum Washable Permanent Filter

    Questions About Custom Filters

    Common questions about ordering a custom filter.

    How do I measure my filter slot for a custom filter?

    Measure the slot opening itself, not the existing filter. Get length, width, and depth to the nearest 1/8″. If the existing filter has been trimmed or shimmed, the slot is the authoritative measurement. Our How to Measure guide walks through the process with photos.

    What's the difference between nominal and actual dimensions?

    The nominal size is what you order — the dimensions you enter in the custom-size field. The actual manufactured filter is typically about 1/2″ smaller than nominal on each face dimension so it slides into the slot without binding. For a 1″ depth filter, the actual depth is typically 3/4″. This is standard industry practice. Measure and order the nominal size — the actual-size tolerance is handled in production.

    Should I round up or down if I'm between sizes?

    Round up to the nearest 1/8″. Rounding down creates gap, which creates bypass — the exact problem custom filters are designed to solve. Rounding up gives the filter more material to seat against; the 1/2″ nominal-to-actual tolerance means the filter still slides in.

    How long does a custom filter order take to ship?

    Typical delivery 6 to 10 business days: 3 to 5 for production, 2 to 5 for shipping via UPS or FedEx. Production happens before shipping. Current timing on the production schedule page.

    Can I rush a custom filter order?

    Rush production and expedited shipping are available for many sizes. Call 866-469-8556 before placing the order so we can confirm the lead time is achievable for your specifications. For commercial and institutional orders with compliance deadlines, contact us first and we'll build the schedule around your need-by date.

    What if my custom filter doesn't fit when it arrives?

    The Filter Fit Guarantee covers custom filters. If it doesn't fit, contact us within 30 days and we'll make it right, including rebuilding to corrected dimensions. One flat $30 fee covers exchanges. Most fit issues trace back to measuring the existing filter instead of the slot.

    Can I return a custom filter if I don't need it?

    Custom filters are made to specification and aren't returnable for refund the way stocked filters are. The Filter Fit Guarantee covers fit issues, damage, and spec mismatches. See the refund policy.

    Who actually manufactures these custom filters?

    Custom filters on RememberTheFilter.com are built by AAF Flanders, Koch Filter, Smith Filter Corporation, NaturalAire, or produced to our PrimeShield specifications — depending on the specific filter type you're ordering. The product description on each listing identifies the manufacturer. Each custom filter ships direct from the plant that built it.

    How do custom filter prices compare to standard sizes?

    Custom filters are priced higher than equivalent standard sizes because each order triggers production. Case pricing keeps the per-filter cost reasonable, which is why most custom filters are sold as cases. For customers with non-standard slots, the long-term cost of stocked-size workarounds — trimming, stacking, gap-filling, and the equipment damage that follows — is higher than paying custom-filter pricing upfront.

    What's the largest custom filter you can build?

    The size range shown on this listing covers the standard custom program. For larger commercial or industrial specifications, or for sizes outside the listed range, request a quote and we'll confirm what can be produced — commercial and industrial custom runs regularly exceed residential size limits.

    How often should I change or maintain a custom filter?

    Maintenance depends on the filter type. Pleated: 1″ every 1-3 months, 2″ every 2-3 months, 4″ or deeper every 6-12 months. Fiberglass: every 30 days. Washable: clean every 30-90 days, replace when media shows damage. Homes with pets, smokers, wildfire smoke, or higher occupancy should service more often. Standing replacement orders can be scheduled at your cadence.

    Do you ship custom filters to Alaska, Hawaii, or a PO box?

    Alaska and Hawaii: yes, at carrier rates calculated at checkout. Free shipping on orders $50+ applies to the lower 48 contiguous states only. PO boxes cannot be accepted because filter boxes are physically oversized. A street address or business address is required for delivery.

    Do you offer bulk custom filter pricing for facilities?

    Yes. For properties with multiple non-standard slot sizes or standing-order needs, we consolidate the spec and quote volume pricing. Schools, clinics, multifamily properties, and government facilities with older HVAC equipment are a significant share of custom filter orders. Request a quote with your size list and estimated annual volume.

    Are custom filters available tax-exempt for schools and government?

    Yes. Submit your certificate through the tax-exempt purchases page and we'll set up your account so future orders ship tax-free. POs and government procurement supported for established accounts.

    Ready to Order

    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.