Trane Furnace Filter Size by Model Number: Find Your Exact Replacement Filter

Last Updated: March 2026 | Need help? Call us at 910-401-3910

Trane furnace filters are some of the most confusing to buy because Trane uses proprietary whole-house filter sizes that don't match standard dimensions. A Trane "21×27×5" or "22.7×20×4.7" filter isn't something you'll find at your local hardware store. This guide shows you exactly how to find your Trane filter by furnace model number, filter cabinet model, or the part number on your existing filter.

Quick Answer: How Trane Filter Sizing Works

Trane systems use two main types of whole-house media filters, plus standard return vent filters:

The key difference: Perfect Fit filters expand like an accordion and install into a Trane filter rack or cabinet, while QuikBox filters are flat media panels that slide into the newer QuikBox cabinet. These two systems are not interchangeable.

Step 1: Identify Your Trane Filter System

Option A: Check the Part Number on Your Current Filter

Remove your existing filter and look for the part number printed on the frame. This is the fastest way to identify your replacement:

• Starts with BAYFTFR → You have a Perfect Fit Expandable filter
• Starts with BAYFTAH → You have a Perfect Fit filter (older designation)
• Starts with FLRQB5 → You have a QuikBox filter
• Shows a standard size like 20×25×1 → You have a standard return vent filter

Option B: Check the Filter Cabinet or Rack

Walk to your Trane furnace and look for the filter compartment:

• Perfect Fit cabinet — Older rectangular cabinet or filter rack, filter expands to fill the space. The rack may have an "FLR" model number on the label.
• QuikBox cabinet — Newer, more compact design. The cabinet label says "QuikBox" and the model number starts with FLRQB or QUIK.
• No separate cabinet — You use a standard return vent filter in the slot at the furnace intake or return duct.

Option C: Use Your Furnace Model Number

Trane furnace model numbers can point you in the right direction:

• S9V2, S9X2 → XV/XC95 premium models — commonly paired with Perfect Fit or QuikBox
• S9V1, S8X1 → XR95/XR80 mid-range — commonly paired with Perfect Fit or QuikBox
• S8B1, S8B2 → XB80/Legacy budget models — often use standard return vent filters
• TUH1, TUH2 → Older Trane gas furnaces — Perfect Fit or standard

Step 2: Match Your Filter Part Number to the Correct Replacement

Trane Perfect Fit Expandable Filters (BAYFTFR / BAYFTAH Series)

Perfect Fit filters are Trane's signature expandable media filters. They compress flat for shipping and expand accordion-style when installed. These are thick whole-house filters that last 6–12 months.

The most popular Trane filter: The BAYFTFREXM2 (sometimes called "Perfect Fit 5") is by far the most commonly ordered Trane filter. It's the 21×27×5 expandable filter that fits the majority of Trane residential systems with media cabinets.

BAYFTFREXM2 vs. BAYFTFR21M — What's the difference? The BAYFTFREXM2 replaced the older BAYFTFR21M. They are the same size and fit the same filter rack. If your system originally came with a BAYFTFR21M, the BAYFTFREXM2 is the current replacement.

Shop All Trane Perfect Fit Filters →

Trane QuikBox Filters (FLRQB5 Series)

The QuikBox is Trane's newer, more compact media filter system. It's a flat (non-expandable) filter panel that slides into a dedicated QuikBox cabinet. QuikBox cabinets are commonly installed with Trane's newer furnace models (2018 and later). QuikBox filters are our #1 selling Trane product category.

How to Read QuikBox Part Numbers

Every QuikBox part number follows the same pattern: FLRQB5 + [cabinet code] + [BTU code] + M + [MERV rating]

• AH = Air Handler style, 21" wide cabinet (filter width ~20")
• DN = Downflow/narrow style, 17" wide cabinet (filter width ~20")
• FR = Full-range style, 24.5" wide cabinet (filter width ~26")
• M11 = MERV 11  |  M08 = MERV 8

Shop All Trane QuikBox Filters →

Standard Return Vent Filters for Trane Systems

Many Trane furnaces — especially Legacy, XB, and older XR series models — use standard return vent filters without a whole-house media cabinet. If your Trane system has a standard filter slot (no separate cabinet), you simply need to match the nominal size printed on your current filter.

Common sizes used with Trane systems include 16×25×1, 20×20×1, 20×25×1, and 16×20×1. All are available in MERV 8, MERV 11, and MERV 13.

Shop Standard Filters by Size → | Use Our Filter Size Chart →

Trane Filter Rack to Filter Cross-Reference

Some older Trane filter racks use "FLR" model numbers that can be confusing — the FLR number is the rack, not the filter. Use this cross-reference to find the correct replacement filter for your rack:

Trane Furnace Models and Typical Filter Systems

This table shows which filter system is most commonly paired with each Trane furnace series. Remember that the filter cabinet is a separate component — always verify by checking the cabinet label or your existing filter.

Trane XV / XC Series (Premium)

Trane XR Series (Mid-Range)

Trane XB / Legacy Series (Value)

How to Read Your Trane Furnace Model Number

Trane model numbers contain useful information encoded in the characters:

Example: S9V2B080U3PSB

• S = Series identifier
• 9 = 90%+ AFUE efficiency class
• V2 = Variable speed, two-stage
• B = Design revision
• 080 = BTU input (80,000 BTU)
• U = Upflow configuration
• 3 = Cabinet width (3 = 21", 4 = 24.5")
• P = Motor type

The cabinet width digit matters for QuikBox filter sizing. A width code of 3 indicates a 21" wide cabinet — this uses AH-size QuikBox filters (like FLRQB5AH23M11) with filter widths around 20". A width code of 4 indicates a 24.5" wide cabinet — this uses FR-size QuikBox filters (like FLRQB5FR17M11) with filter widths around 26".

Finding the Part Number on Your Current Trane Filter

Perfect Fit (BAYFTFREXM2 / BAYFTAH) filters: Look on the side of the compressed filter before expanding it. The part number and actual dimensions are printed on the cardboard band that holds the accordion folds together.

QuikBox (FLRQB5) filters: The part number is printed on the filter frame, usually on the side facing you when installed. Look for "FLRQB5" followed by the cabinet code, size, and MERV designation.

Standard filters: Read the nominal dimensions on the frame (example: 20×25×1).

Frequently Asked Questions

What is the most common Trane furnace filter?

The BAYFTFREXM2 (also known as the Perfect Fit 5 or 21×27×5 expandable filter) is the most widely used Trane filter for older systems. For newer Trane systems (2018+) with QuikBox cabinets, the FLRQB5AH23M11 (22.7×20×4.7 MERV 11) is the top seller.

Can I use a higher MERV rating in my Trane system?

For QuikBox filters, both MERV 8 and MERV 11 are available. The QuikBox cabinet is specifically designed to handle MERV 11 without stressing your system. For Perfect Fit filters, Trane offers MERV 8 as standard. For standard return vent filters, most Trane furnaces with ECM or variable-speed blowers can handle MERV 11 or MERV 13. Older single-stage systems should stick with MERV 8 or MERV 11.

How often should I change my Trane filter?

• Perfect Fit (BAYFTFREXM2 / BAYFTAH): Every 6–12 months
• QuikBox (FLRQB5): Every 6–12 months
• Standard 1" filters: Every 30–90 days depending on MERV rating

Homes with pets, smokers, or allergy sufferers should change on the shorter end of these ranges.

My Trane filter part number starts with FLR but it's not a QuikBox. What is it?

Some older Trane filter racks used "FLR" prefix model numbers for the rack itself. The filter that goes IN the rack is a Perfect Fit (BAYFTAH or BAYFTFR series). Match your rack:

• FLR06069 → uses BAYFTFR17M (17.5×27×5)
• FLR06070 → uses BAYFTAH26M (21×26×5)
• FLR06072 → uses BAYFTAH21M (21×21.5×5)

Are Trane and American Standard filters the same?

Yes. Trane and American Standard are both manufactured by Trane Technologies and use identical filter systems. If you have an American Standard furnace, use this same guide — the filter part numbers (BAYFTFREXM2, BAYFTAHEXM2, FLRQB5, etc.) are the same.

I can't find my Trane filter at the hardware store. Why?

Trane Perfect Fit and QuikBox filters use proprietary dimensions (21×27×5, 22.7×20×4.7, etc.) that aren't standard sizes. Big box stores typically only carry standard 1" and 4" filters in common dimensions like 16×25 and 20×25. Trane whole-house filters need to be purchased from an HVAC supplier or online retailer like Atomic Filters.

What is the difference between BAYFTFREXM2 and BAYFTFR21M?

The BAYFTFREXM2 replaced the older BAYFTFR21M. They are the same size (21×27×5) and fit the same filter rack. If your system came with a BAYFTFR21M, the BAYFTFREXM2 is the current replacement.

Still Not Sure Which Trane Filter You Need?

Trane's proprietary sizing makes ordering confusing, but we deal with it every day. Here's how to get the right filter fast:

📞 Call us at 910-401-3910 — Give us your furnace model number, filter cabinet/rack model, or the part number on your current filter.

📧 Email info@atomicfilters.com — Send a photo of your current filter label or your filter cabinet sticker and we'll identify your exact replacement.

🔍 Search our site — Enter any Trane part number (BAYFTFREXM2, FLRQB5AH23M11, BAYFTAH26M, etc.) directly in our search bar.