Hart & Cooley Type B gas vent pipe and fittings are Underwriters Laboratories-tested and listed to Standard 441 for use with listed gas-fired appliances that have been certified for use with Type B gas vent. B-Vent is intended for neutral or negative draft applications. It is designed for vertical installations (including laterals) but may be used for horizontal applications with a draft-inducing fan located such that all indoor portions of the vent are under negative pressure.