Water heater venting system and components thereof all made of plastic comprised of a vent kit body, a concentric vent pipe and a rain cap; pipe fittings and vent pipe, all made of plastic for ventilation applications; rain cap made of plastic; concentric ventilation pipe made of plastic; flue gas ventilation kit for venting tankless water heaters and components thereof, all made of plastic comprised of a plastic exhaust pipe, a fresh air intake pipe, a rain cap, and a ventilation kit body consisting of a front clamshell, a back clamshell, an access panel, a pipe socket, an air vent retainer, an air vent and a reducing elbow; ventilation kits for hot water heating systems comprised of a plastic exhaust pipe, and a ventilation kit body consisting of a front clamshell, a back clamshell, an access panel, a pipe socket, an air vent retainer and an air vent