Listing we opened and checked. Match the diameter, length and both fittings on this page before you order. The price is on Amazon; we do not print one.
Nordic Hot Tubs OEM 31CARTRIDGE spa filter (C-4326)
Nordic Hot Tubs (models dated after 7/99)
Replacement numbers
Unicel C-4326, Pleatco PRB25-IN
Fits Nordic Hot Tubs OEM 31CARTRIDGE.
Diameter 4-15/16" (125 mm)Length 13-5/16" (338 mm)25 sq ft6 models listedUnicel C-4326
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| Unicel | C-4326 |
|---|---|
| Pleatco | PRB25-IN |
| Filbur | FC-2375 |
| Top | 2-1/8" (54 mm) / open |
| Bottom | 2-1/8" (54 mm) / open |
Bottom: 2-1/8" (54 mm) / open
Drawn to scale from the listed diameter and length and open-end sizes. Handles, threads and closed ends are drawn as symbols, not to scale. 25 sq ft media.
Nordic Hot Tubs (models dated after 7/99) is the group name on the Nordic Hot Tubs row C-4326 cartridge. Match these numbers: OEM 31CARTRIDGE; Unicel C-4326; Pleatco PRB25-IN; Filbur FC-2375. 4-15/16" across, 13-5/16" long, top 2-1/8" / open, bottom 2-1/8" / open, 25 sq ft.
Catalog note for 31CARTRIDGE: Unicel and Filbur both say this is for Nordic models dated after 7/99. Nordic Hot Tubs' own 2023 filter chart lists it as CARTRIDGE (sold as 31CARTRIDGE, 25 sq ft, in Nordic's 2022 parts list) = Unicel C-4326, Pleatco PRB25-IN, Filbur FC-2375, Waterway 817-2500. The chart says the Crown II, Crown XL, Escape MS/SE/LS, Impulse DP, Rendezvous LS, 110 Sport and Warrior XL models switched to CARTRIDGE-E (45 sq ft) after September 2021.
Nordic Hot Tubs applications recorded for this cartridge: Nordic Crown, years before 2008, listed by Nordic Hot Tubs filter chart (2023) (CARTRIDGE, 25 sq ft); Nordic Warrior, years before 2008, listed by Nordic Hot Tubs filter chart (2023) (CARTRIDGE, 25 sq ft); Nordic DLX, DLX w HS, Nordic, Nordic w HS, Omni, Insider, Quadra, no year range printed, listed by Nordic Hot Tubs filter chart (2023) (CARTRIDGE, 25 sq ft); Nordic Escape, Escape R, Escape Pre, Escape Pre R, no year range printed, listed by Nordic Hot Tubs filter chart (2023) (CARTRIDGE, 25 sq ft); Nordic Impulse, Rendezvous 1, Rendezvous 2, Sport, no year range printed, listed by Nordic Hot Tubs filter chart (2023) (CARTRIDGE, 25 sq ft); Nordic Crown II, Crown XL, Escape MS, SE, LS, Impulse DP, Rendezvous LS, 110 Sport, Warrior XL, 110 Warrior XL, years before Sept 2021, listed by Nordic Hot Tubs filter chart (2023) (CARTRIDGE, 25 sq ft).
Hold C-4326 next to 4CH-935 differs by Unicel 4CH-935, Pleatco PWW35L, no Filbur number, 9-1/4" long, top v-groove semi-circular handle, bottom 2" female SAE thread, 35 sq ft, OEM CARTRIDGE-T35, note says Nordic Hot Tubs' own 2023 filter chart lists CARTRIDGE-T35 as Unicel 4CH-935, Pleatco PWW35L and Waterway 817-4035, with no Filbur number. Nordic's owner's manual gives the same size: 9-1/4" long, 4-15/16" across, handle top, 2" SAE female thread, 35 sq ft. Nordic's 2022 parts list sells it as 31CARTRIDGE-T35 for the Teleweir housing. Unicel's spec table says it fits a 1-1/2" male SAE stand pipe..
Left blank on purpose: Nordic's chart does not use the catalogs' 7/99 date and gives no years for most models; Nordic's owner's manual lists Impulse under CARTRIDGE-E while the chart lists it here.
Where those figures are printed: Unicel 2026 Replacement Guide on C-4326 (OEM cross reference (Nordic Hot Tubs section), PDF p.46 (printed p.42); spec table PDF p.9 (printed p.5)). Pleatco 2023 Catalog on C-4326 (Unicel-to-Pleatco cross reference, PDF p.47 (C-4326 = PRB25-IN)). Filbur Catalog & Reference Guide on C-4326 (Product by Pool/Spa Manufacturer (OEM), Nordic Hot Tubs, printed p.44 (PDF p.23)). Nordic Hot Tubs filter chart (2023) on C-4326 (CARTRIDGE row: Unicel C-4326, Pleatco PRB25-IN, Filbur FC-2375, Waterway 817-2500; model list, before/after Sept 2021 notes). Nordic Hot Tubs 2022 service parts list on C-4326 (31CARTRIDGE, Cartridge, Filter, 25 SQ FT).
Hot tubs listed for this cartridge
The rest of the Nordic Hot Tubs model list is the Nordic Hot Tubs filter by model and year lookup.
| Model / system | Years | Listed by |
|---|---|---|
| Nordic Crown (CARTRIDGE, 25 sq ft) | before 2008 | Nordic Hot Tubs filter chart (2023) |
| Nordic Warrior (CARTRIDGE, 25 sq ft) | before 2008 | Nordic Hot Tubs filter chart (2023) |
| Nordic DLX, DLX w HS, Nordic, Nordic w HS, Omni, Insider, Quadra (CARTRIDGE, 25 sq ft) | not given | Nordic Hot Tubs filter chart (2023) |
| Nordic Escape, Escape R, Escape Pre, Escape Pre R (CARTRIDGE, 25 sq ft) | not given | Nordic Hot Tubs filter chart (2023) |
| Nordic Impulse, Rendezvous 1, Rendezvous 2, Sport (CARTRIDGE, 25 sq ft) | not given | Nordic Hot Tubs filter chart (2023) |
| Nordic Crown II, Crown XL, Escape MS, SE, LS, Impulse DP, Rendezvous LS, 110 Sport, Warrior XL, 110 Warrior XL (CARTRIDGE, 25 sq ft) | before Sept 2021 | Nordic Hot Tubs filter chart (2023) |
Check the cartridge you removed
Measure diameter, length, and both ends, then compare them with the figures above. The steps are in the measuring guide. Why the bottom decides whether it seals: open-end vs threaded filters. Power, the retainer, and not running the spa empty: how to install a cartridge. Number formats: how Filbur, Unicel and Pleatco numbers compare.
The same C-4326 number is also on the Hot Spring, Hot Spot, Jacuzzi, Beachcomber, PDC Spas pages.
Other Nordic Hot Tubs cartridges
- 4CH-935 cartridge, 4-15/16" (125 mm) × 9-1/4" (235 mm)
All 3 Nordic Hot Tubs spa filters
Every number on this row, on one screen: cross-reference lookup. Published clean and replace intervals for this cartridge, and a buy link for the numbers above: replacement schedule and reorder. The interval comparison by brand: calculator.
Cleaner and test strips
Hose rinse and soak steps are in how to clean a cartridge. Named cleaners and strips are in filter cleaners and test strips.
Filter cleaner and test strips
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Leisure Time O Filter Clean Cartridge Cleaner Listing title: cartridge cleaner, 32 fl oz.
-
SpaGuard Filter Cleaner Listing title: filter cleaner for spas and hot tubs, 1 quart.
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AquaChek SPA 6-in-1 Test Strips Listing title: reads total bromine, total chlorine, free chlorine, pH, total alkalinity and total hardness.
Unicel C-4326 Listing we opened and checked. Match the diameter, length and both fittings on this page before you order. The price is on Amazon; we do not print one.
Sources
- Unicel 2026 Replacement Guide: OEM cross reference (Nordic Hot Tubs section), PDF p.46 (printed p.42); spec table PDF p.9 (printed p.5) (PDF)
- Pleatco 2023 Catalog: Unicel-to-Pleatco cross reference, PDF p.47 (C-4326 = PRB25-IN) (PDF)
- Filbur Catalog & Reference Guide: Product by Pool/Spa Manufacturer (OEM), Nordic Hot Tubs, printed p.44 (PDF p.23) (PDF)
- Nordic Hot Tubs filter chart (2023): CARTRIDGE row: Unicel C-4326, Pleatco PRB25-IN, Filbur FC-2375, Waterway 817-2500; model list, before/after Sept 2021 notes (PDF)
- Nordic Hot Tubs 2022 service parts list: 31CARTRIDGE, Cartridge, Filter, 25 SQ FT (PDF)
Not in sources: Nordic's chart does not use the catalogs' 7/99 date and gives no years for most models; Nordic's owner's manual lists Impulse under CARTRIDGE-E while the chart lists it here.