Centrotherm’s universal B-vent cap is comprised of a two-part design that allows combustion air to be pulled into the B-vent while keeping rain out. When combined, the cap can mount to the top of any B-vent from 3” through 6” diameters, allowing for any single InnoFlue flex or rigid vent from 2” through 4” diameters to be run through it. Multiple exhausts through the cap also are an option. Centrotherm.