The standard the rest of the shelf is built on.

Big Blue is the large-format housing standard for whole-house filtration: a heavy-duty polypropylene housing that takes any standard 20″ × 4.5″ cartridge — sediment, carbon and specialty stages from Pentek and most other makers. The cap carries a pressure-relief button, so a cartridge change doesn't fight trapped pressure.

Bought on its own, this is the housing for adding a stage to an existing system or replacing a tired one. Bought with a cartridge, it's the start of a system Tandem can size, install and maintain for you.

• Standard 20-inch Big Blue format — accepts 4.5-inch-diameter cartridges
• Maximum dimensions: 23⅜″ high × 7¼″ wide — allow clearance below to drop the sump for cartridge changes
• Heavy-duty polypropylene construction
• Pressure-relief button in the cap for easier cartridge changes
• Rated to 90 psi maximum pressure, 100 °F maximum temperature
• Certified to NSF/ANSI 42 for materials and structural integrity (Pentair specification)
• Ports: 3/4-inch, 1-inch or 1½-inch NPT — order the size that matches your line; 1-inch is the common whole-house choice
• Works with Pentek and other brands' standard cartridges

Best for: adding or replacing a whole-house stage; the foundation under a FloPlus Protect cartridge or a sediment/carbon stage.
Not for: slim or proprietary housings' cartridges (measure first — we check at a Well Check). A housing is never a treatment claim on its own: performance comes from the cartridge you choose, and each cartridge's own verified claims travel with it.

From Tandem: tell us what your water test says and we'll pair the housing with the right stage — and put its cartridge on your reminder schedule.