Z-Vent 2SVSNA04.5 Z-Flex 4-inch Universal Adaptor Takagi Paloma Rheem Noritz 4" Universal Adaptor: Modine, Nordyne, QuietSide Has seals on both ends (female on both ends) Connects the tankless water heater to the 4" Z-Flex Z-Vent Stainless Steel Venting Rated AL29-4C and is approved for Category I (vertical only), II, III & IV applications