The Pentair Pentek RFC-20BB is a 20-inch radial flow carbon cartridge that reduces chlorine taste and odor across your whole house. A bed of granular activated carbon (GAC) is held between a porous polyethylene outer shell and a spun polypropylene core, so water flows radially through the carbon for effective taste and odor reduction. The radial flow design keeps pressure drop very low, under 1 psi at 4 gpm, while significantly reducing the release of carbon fines that are common with standard GAC cartridges. With more than 100,000 gallons of chlorine taste and odor capacity, it is built for point-of-entry and other high-flow applications and can provide up to a year of service before replacement. The 20" x 4.5" cartridge fits Pentair Pentek Big Blue and other heavy duty housings and replaces most 20-inch carbon cartridges. The RFC-BB and RFC20-BB are tested and certified by NSF International to NSF/ANSI Standard 42 for material requirements. Replace every 6 to 12 months or when chlorine taste and odor return. This listing is a Pack of 6.