Home › Hot Spring › C-4326 cartridge (OEM 33521)
Hot Spring OEM 33521 spa filter (C-4326)
Listed for: Hot Spring (Watkins)
Fits Hot Spring OEM 33521 cited
Ø 4-15/16"L 13-5/16"25 sq ft| Unicel | C-4326 |
|---|---|
| Pleatco | PRB25-IN |
| Filbur | not sourced |
| Top | 2-1/8" / open |
| Bottom | 2-1/8" / open |
Retailer search links — see disclosure. Verify dimensions before ordering.
How to confirm this is your filter
Pull your current cartridge and measure it end to end, including any handle, and across the widest point of the pleats. This cartridge measures 4-15/16" in diameter and 13-5/16" long, with a 2-1/8" / open on top and a 2-1/8" / open on the bottom. The bottom fitting matters most: a cartridge with the right diameter but the wrong thread or open-end size will not seal in the filter housing, letting unfiltered water bypass the media.
The 25 sq ft rating describes the pleated media area. Hot Spring housings are designed around a particular cartridge, so choose a replacement with the same size and fittings rather than a larger area rating. Unicel C-4326 and Pleatco PRB25-IN are cross-referenced to each other in the Pleatco 2023 catalog, so either should fit the same housing.
Similar-diameter Hot Spring cartridges
- C-5431 cartridge (OEM 31233) — 5-1/8" × 10-1/4"
Sources
- Unicel 2026 Replacement Guide — OEM Cross Reference, PDF p.38; spec table PDF p.8 (PDF)
- Pleatco 2023 Catalog — Unicel-to-Pleatco cross reference, PDF p.43 (PDF)
Not in sources: no Filbur equivalent sourced; no model-year range in source.