Which filter does my Nordic hot tub take? Lookup by model and year
Nordic’s own spa filter chart uses five cartridges. Most Escape, Sport, Impulse, Rendezvous, Warrior and older Crown spas take the 25 sq ft CARTRIDGE (4-15/16" × 13-5/16", open both ends): Unicel C-4326, Pleatco PRB25-IN, Filbur FC-2375. Crown II, Crown XL, Escape MS/SE/LS, Impulse DP, Rendezvous LS, 110 Sport and Warrior XL spas built after September 2021 take the 45 sq ft CARTRIDGE-E (5-5/16" × 10-1/8"): Unicel C-5345, Pleatco PLBS50-M, Filbur FC-2970M. Crown (after 2014), D’Amour, Encore, Jubilee, Retreat and Stella spas take the threaded 35 sq ft CARTRIDGE-T35: Unicel 4CH-935, Pleatco PWW35L. Bella spas take the slim CARTRIDGE14.5 or CARTRIDGE-BELLA.
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The cartridges, with equivalents
| Factory part | What it is | Aftermarket equivalents (Nordic chart and catalogs) | Rated area | Our page |
|---|---|---|---|---|
| CARTRIDGE (31CARTRIDGE) | Open both ends (2-1/8"); most Nordic spas, and the Sept 2021 switch models built before the change | Unicel C-4326 (4-15/16" × 13-5/16"); Pleatco PRB25-IN; Filbur FC-2375; Waterway 817-2500 | 25 sq ft | C-4326 |
| CARTRIDGE-E (31CARTRIDGE-E) | Open both ends (2-1/8"), 5-5/16" × 10-1/8" (Nordic manual); Crown II, Crown XL, Escape MS/SE/LS, Impulse DP, Rendezvous LS, 110 Sport, Warrior XL built after Sept 2021 For Escape SE after Sept 2021 the chart prints PLBS50 rather than PLBS50-M. | Nordic’s chart prints Unicel C-5345AM, Pleatco PLBS50-M, Filbur FC-2970M. The Unicel guide lists C-5345 (same size, 45 sq ft) | 45 sq ft (Nordic manual, Unicel); Pleatco rates PLBS50 at 50 | not listed |
| CARTRIDGE-T35 (31CARTRIDGE-T35) | Handle top, 2" SAE female thread, 4-15/16" × 9-1/4"; sits in the Teleweir skimmer. Crown (after 2014), D’Amour, Encore, Jubilee, Retreat and Stella models Pleatco’s spec table prints PWW35L as 5" × 8-1/2" with a 1-1/2" bottom. | Unicel 4CH-935; Pleatco PWW35L; Waterway 817-4035. Filbur: none (the chart prints NA) | 35 sq ft | 4CH-935 |
| CARTRIDGE14.5 (31CARTRIDGE14.5) | Slim “Space Saver” cartridge, 2-7/8" × 17-1/16", 1-1/16" open ends; Bella and Bella MS | Unicel C-2302; Pleatco PRB14.5; Filbur FC-2320. Waterway: none | 14.5 sq ft (Pleatco: 15) | not listed |
| CARTRIDGE-BELLA (31CARTRIDGE-BELLA) | Slim cartridge, 2-7/8" × 19-9/16" per Nordic’s manual (19-1/2" in the chart and catalogs), 1-1/16" open; Bella MS after 2017 Unicel’s 2026 price list says “C-2612 USE C-2608”. | Unicel C-2612; Pleatco PRB12-4; Filbur FC-2340; Waterway 817-3640 | 20 sq ft (Nordic); 12 sq ft (Unicel, Pleatco) | not listed |
| No Nordic number (catalogs only) | Open both ends; Unicel and Filbur list it for Nordic models dated before 7/99. Not in Nordic’s chart | Unicel C-4301 (4-15/16" × 14-7/8"); Pleatco PMT27.5; Filbur FC-1610 | 28 sq ft | C-4301 |
The Nordic part numbers and their Unicel, Pleatco, Filbur and Waterway equivalents are printed in Nordic Hot Tubs’ own 2023 filter chart. Sizes are from Nordic’s 2024 owner’s manual where it gives them, otherwise from the Unicel 2026 guide. Nordic’s parts list sells each one with a “31” prefix (for example 31CARTRIDGE-T35).
Find your model and year
This table is Nordic Hot Tubs’ own “Filter Cartridges List by Model” (March 2023 edition). Nordic gives a date only where a model changed filter; “Not given” means the chart lists the model without years.
| Model | Built | Nordic filter |
|---|---|---|
| Crown | Before 2008 | CARTRIDGE (25 sq ft, open both ends) |
| Crown | After 2014 | CARTRIDGE-T35 (35 sq ft, threaded) |
| 110 Crown | Not given | CARTRIDGE-T35 |
| Warrior | Before 2008 | CARTRIDGE |
| DLX, DLX w HS, Nordic, Nordic w HS, Omni, Insider, Quadra | Not given | CARTRIDGE |
| Escape, Escape R, Escape Pre, Escape Pre R | Not given | CARTRIDGE |
| Impulse, Rendezvous 1, Rendezvous 2, Sport | Not given | CARTRIDGE (the owner’s manual lists Impulse under CARTRIDGE-E; see below) |
| Crown II, Crown XL, Escape MS, Escape SE, Escape LS, Impulse DP, Rendezvous LS, 110 Sport, Warrior XL, 110 Warrior XL | Before Sept 2021 | CARTRIDGE |
| Same models as the row above | After Sept 2021 | CARTRIDGE-E (45 sq ft, open both ends) |
| D’Amour: 110 D’Amour, D’Amour MS, D’Amour SE | Not given | CARTRIDGE-T35 |
| Encore: Encore, Encore Pre, 110 Encore, Encore MS, SE, LS | Not given | CARTRIDGE-T35 |
| Jubilee: 110 Jubilee, Jubilee MS, SE, LS | Not given | CARTRIDGE-T35 |
| Retreat: Retreat, 110 Retreat, Retreat MS, Retreat SE | Not given | CARTRIDGE-T35 |
| Stella: Stella, 110 Stella, Stella MS, Stella SE | Not given | CARTRIDGE-T35 |
| Bella, Bella MS | Not given | CARTRIDGE14.5 (14.5 sq ft “Space Saver”) |
| Bella MS | After 2017 | CARTRIDGE-BELLA (20 sq ft per Nordic) |
How many filters, and how they come out
Nordic’s 2024 owner’s manual says the hot tub filter sits either under a floating weir, which you pull up and turn counter-clockwise to reach the cartridge, or in a basket you can see. The threaded CARTRIDGE-T35 sits in a Teleweir skimmer. Nordic’s 2022 parts list sells two versions of the Teleweir cage, one for 2017 and older tubs and one for 2018 and newer. The cartridge number, 31CARTRIDGE-T35, is the same for both. The manual says to rinse the spa filter with a high-pressure hose weekly and soak it in a filter cleaner monthly.
Where the sources disagree
- Crown, 2008 to 2014. The chart lists Crown “before 2008” under CARTRIDGE and “after 2014” under CARTRIDGE-T35. A Crown built from 2008 to 2014 is not covered. The owner’s manual says “all Crown models” take the T35, yet it also lists the Crown II and Crown XL under CARTRIDGE-E. Check the old cartridge: threaded with a handle means T35; open at both ends means CARTRIDGE or CARTRIDGE-E.
- Impulse. The chart lists Impulse under CARTRIDGE and Impulse DP under the Sept 2021 change. The manual lists both Impulse and Impulse DP under CARTRIDGE-E.
- CARTRIDGE-E: 45 or 50 sq ft. Nordic’s manual, Unicel’s C-5345 and Hot Tub Outpost’s 31CARTRIDGE-E listing all say 45 sq ft. Nordic’s 2022 parts list files it under a “50 SQ FT Filters & Parts” heading, and Pleatco rates PLBS50 at 50. Filbur prints FC-2970 at 50 in one table and 45 in another. The size is the same in every source.
- C-5345AM. Nordic’s chart prints “C-5345AM”, which is not in the Unicel 2026 guide; the guide lists C-5345 at the same size.
- CARTRIDGE-BELLA rating and number. Nordic’s manual rates it 20 sq ft. Unicel rates C-2612 at 12 (13 in some tables), Pleatco rates PRB12-4 at 12, and Unicel’s price list says to use C-2608 (8 sq ft) in place of C-2612. Nordic’s 2021 chart printed no aftermarket numbers for this cartridge; the 2023 chart added them.
- The pre-7/99 cartridge. Unicel and Filbur list a 28 sq ft C-4301 (FC-1610) for Nordic models dated before 7/99 and C-4326 after. Nordic’s chart does not mention C-4301 or the 7/99 date.
- PWW35L size. Nordic and Unicel give 4-15/16" × 9-1/4" with a 2" female SAE thread; Pleatco’s spec table prints 5" × 8-1/2" with a 1-1/2" fitting for PWW35L. Unicel notes 4CH-935 screws onto a 1-1/2" male SAE stand pipe, which may explain the different figure.
- CARTRIDGE-E housing. Hot Tub Outpost says the 31CARTRIDGE-E fits filter assemblies 30100706 and 30100708. Nordic’s parts list names those as the 25 sq ft housings and lists a separate Elite canister, 30100709, for the CARTRIDGE-E.
Known limits
- Nordic gives model years only for the Crown, the Warrior, the Bella MS and the Sept 2021 change. For other models the chart names the filter without dates.
- Models not in the 2023 chart (for example any introduced after March 2023) are not covered here.
- CARTRIDGE-E, CARTRIDGE14.5 and CARTRIDGE-BELLA do not have their own Nordic rows in our dataset yet, so they have no cartridge page to link to.
How to confirm yours
- Read the number on the old cartridge’s end cap and search it here.
- No number? Look at the ends: a handle with a threaded bottom is the T35; open at both ends and 13-5/16" long is the CARTRIDGE; open at both ends, fatter (5-5/16") and 10-1/8" long is the CARTRIDGE-E. Measure as in our filter-size guide.
- Compare the result with the Nordic Hot Tubs brand table, then see how often to clean a hot tub filter.
Why one cartridge size can carry two different square-foot ratings: our explainer with Unicel’s pleat-count table.
Sources
- Nordic Hot Tubs: Filter Cartridges List by Model, 2023 (models, Nordic numbers, Unicel/Pleatco/Filbur/Waterway equivalents)
- Nordic Hot Tubs: Filter Cartridges List by Model, 2021 edition (earlier chart; no CARTRIDGE-BELLA equivalents)
- Nordic Hot Tubs: Filter cartridge listed by model (page linking the chart)
- Nordic Hot Tubs: Owner’s manual, 01.2024 (Filter Quick Reference by Model, p. 22; filter care and removal)
- Nordic Hot Tubs: 2022 North American service parts list (31CARTRIDGE, 31CARTRIDGE-E, 31CARTRIDGE-T35, housings and Teleweir cages)
- Hot Tub Outpost: Nordic 31CARTRIDGE-E listing (45 sq ft, 5-5/16" × 10-1/8", models after Sept 2021)
- Unicel 2026 Replacement Guide: Nordic Hot Tubs cross-reference (printed p. 42), spec tables and price list
- Pleatco 2023 Catalog: spec tables (PRB25-IN, PLBS50, PWW35L, PRB14.5, PRB12-4) and Unicel cross-reference
- Filbur Catalog & Reference Guide: Nordic Hot Tubs (printed p. 44) and spec tables
This page summarizes published catalogs and dealer fitment tables; always follow your own spa’s owner’s manual. See our disclaimer and methodology.