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4CH-21 spa filter equivalents
Part number 4CH-21 appears in 1 cross-reference row 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.
Saratoga Spas 4CH-21 cartridge (OEM 20245-238), 4-5/8" (117 mm) × 8" (203 mm), 19 sq ft. Unicel 4CH-21, Pleatco PTL18P4.
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| OEM | 20245-238 |
|---|---|
| Unicel | 4CH-21 |
| Pleatco | PTL18P4 |
| Filbur | FC-0121 |
| Size | 4-5/8" (117 mm) × 8" (203 mm), 19 sq ft |
Sources
- Unicel 2026 Replacement Guide: Saratoga list PDF p.55: 20245-238 = 4CH-21, 4-5/8" x 8", 19 sq ft. Spec table PDF p.7: 158 pleats, 19 sq ft. Price index PDF p.88: 19 sq ft. (PDF)
- Pleatco 2023 Catalog: Spec table PDF p.31: PTL18P4, OEM 20245-238, 18 sq ft. Cross-reference PDF p.47: 4CH-21 = PTL18P4. (PDF)
- Filbur Catalog & Reference Guide: Saratoga section PDF p.25: FC-0121, 4CH-21, 19 sq ft (PDF)
Not in sources: Area 19 (Unicel, Filbur) vs 18 (Pleatco). Length agrees at 8"..
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