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.
33521 spa filter equivalents
Part number 33521 appears in 2 cross-reference rows below. Each row lists the OEM, Unicel and Pleatco numbers that the source documents treat as interchangeable, plus the cartridge size so you can confirm against your old filter.
The same numbers, on one page, are in the cross-reference lookup. A schedule for this part number, and the buy link, are on the replacement schedule and reorder page. Published intervals by brand are in the replace and clean calculator.
Hot Spring C-4326 cartridge (OEM 33521), 4-15/16" (125 mm) × 13-5/16" (338 mm), 25 sq ft. Unicel C-4326, Pleatco PRB25-IN.
Unicel C-4326
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| OEM | 33521 |
|---|---|
| Unicel | C-4326 |
| Pleatco | PRB25-IN |
| Filbur | FC-2375 |
| Size | 4-15/16" (125 mm) × 13-5/16" (338 mm), 25 sq ft |
Sources
- Unicel 2026 Replacement Guide: OEM cross reference (Hot Spring section), PDF p.39 (printed p.35); spec table PDF p.9 (printed p.5) (PDF)
- Pleatco 2023 Catalog: Unicel-to-Pleatco cross reference, PDF p.47 (PDF)
- Filbur Catalog & Reference Guide: Product by Pool/Spa Manufacturer (OEM), Hot Springs, printed p.38 (PDF p.20) (PDF)
Not in sources: no model/model-year fitment in sources.
Full details → · All Hot Spring spa filters · Which fitting you need · How to install it
Hot Spot C-4326 cartridge (OEM 33521), 4-15/16" (125 mm) × 13-5/16" (338 mm), 25 sq ft. Unicel C-4326, Pleatco PRB25-IN.
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.
| OEM | 33521 |
|---|---|
| Unicel | C-4326 |
| Pleatco | PRB25-IN |
| Filbur | FC-2375 |
| Size | 4-15/16" (125 mm) × 13-5/16" (338 mm), 25 sq ft |
Sources
- Unicel 2026 Replacement Guide: OEM cross reference (Hot Springs Spas section), PDF p.39 (printed p.35); spec table PDF p.9 (printed p.5) (PDF)
- Pleatco 2023 Catalog: Unicel-to-Pleatco cross reference, PDF p.47 (PDF)
- Filbur Catalog & Reference Guide: Product by Pool/Spa Manufacturer (OEM), Hot Springs, printed p.38 (PDF p.20) (PDF)
Not in sources: no model/model-year fitment in sources.
Full details → · All Hot Spot spa filters · Which fitting you need · How to install it