FLUE. A pipe, vertical or nearly so in direction, designed to convey all the products of combustion to the outside atmosphere. “Flue-Type A” means tile or fire clay brick-lined chimney or smoke stacks for all types of fuels. “Flue-Type B” means approved vent piping of noncombustible, corrosion-resistant material of adequate strength and heat insulating value and having bell and spigot of other acceptable joints. “Flue-Type C” means single wall vent pipe, of a type approved by Underwriters’ Laboratories, Inc., or by AGA.