Pleatco PWK65 = Unicel C-8465 = Filbur FC-3960

65 sq ft hot tub filter, 8-1/2" diameter × 10-1/2" long. Top: 3" open · Bottom: 3" open. Pleatco application: Watkins Hot Spring Spas upgrade from PWK45N.

Interchangeable cartridges

Unicel C-8465 confirmed by: Pleatco p.47 (Unicel to Pleatco cross reference) Unicel p.21 (Cartridges by series (dimensional listing))
Unicel note: Note: The original was 45 sq. ft. (162 pleats). This replacement has been upgraded to 65 sq. ft.
Filbur FC-3960 confirmed by: Pleatco p.48 (Filbur to Pleatco cross reference) Filbur p.33 (Reverse cross reference (Unicel to Filbur)) Filbur p.12 (Dimensional cartridge listing)

Published dimensions, side by side

Each manufacturer measures a little differently. Compare these with your old cartridge.

As published by	Pleatco PWK65 source	Unicel C-8465 source	Filbur FC-3960 source
Outside diameter	8-1/2"	8-1/2"	8-1/2"
Length	10-1/2"	10-1/2"	10-1/2"
Top end	3" open	3" / open	3" open
Bottom end	3" open	3" / open	3" open
Filter area	65 sq ft	65 sq ft	65 sq ft
Pleats	not listed	234	not listed
Media weight	3 oz/yd²	3 oz/yd²	not listed

Where to buy

Search any retailer for C-8465 or PWK65 or FC-3960. These are the same cartridge under different brand names.

In The Swim (link coming soon)FiltersFast (link coming soon)Amazon (link coming soon)

Some links may be affiliate links. See our disclosure.

OEM part numbers this cartridge replaces

As printed in the cited aftermarket catalogs. Match the number on your old cartridge or in your spa manual exactly.

OEM number	Listed in
`31114`	Pleatco p.35: OEM part # column Unicel p.39: OEM cross reference: Hot Springs Spas Unicel p.60: OEM cross reference: Tiger River
`76136`	Unicel p.30: OEM cross reference: Caldera Spas
`71827`	Unicel p.39: OEM cross reference: Hot Springs Spas
`71828`	Unicel p.39: OEM cross reference: Hot Springs Spas

Hot tub brands that use it

From the spa-manufacturer cross reference in the Unicel 2026 Replacement Guide. A brand may use several sizes, so check your measurements.

Caldera Spas (OEM 76136) Unicel p.30
Hot Springs Spas (OEM 31114, 71827, 71828) Unicel p.39
Tiger River (OEM 31114) Unicel p.60

FAQ

What is the Unicel equivalent of Pleatco PWK65?

The catalogs cross-reference Pleatco PWK65 to Unicel C-8465.

What is the Filbur equivalent of Pleatco PWK65?

The catalogs list Filbur FC-3960.

What size is the PWK65 filter?

Pleatco lists PWK65 as 8-1/2" outside diameter by 10-1/2" long, top: 3" open, bottom: 3" open, 65 sq ft.

Which OEM part numbers does it replace?

Listed OEM numbers: 31114, 76136, 71827, 71828.

Sources: Filbur Product Catalog and Reference Guide (2024) · Filbur Product Catalog and Reference Guide (2024) · Pleatco 2023 Catalog & Cross Reference Guide (Pentair) · Pleatco 2023 Catalog & Cross Reference Guide (Pentair) · Pleatco 2023 Catalog & Cross Reference Guide (Pentair) · Unicel 2026 Replacement Guide. Last checked 2026-10-21.