What material is used to construct the outer wall of a type "B" vent?

Type "B" vents are specifically designed for the venting of gas appliances, typically involving either Category I or IV appliances. The outer wall of a Type "B" vent is made of galvanized steel, which is essential for several reasons.

Galvanized steel is favored because it provides excellent durability and resistance to corrosion, which is critical given the high temperatures and potential exposure to moisture in venting systems. This material can withstand the intense conditions produced by the combustion process and protects the vent from rust and deterioration over time.

In contrast, materials such as stainless steel are commonly used in other venting systems for their high resistance to corrosion and high temperature but are generally more expensive. Copper is not suitable for venting due to its inability to handle the gases produced by combustion effectively, and plastic is not appropriate either, as it cannot withstand the high heat and might melt or become a fire hazard.

Thus, galvanized steel is the ideal choice for the outer wall of a type "B" vent, offering a balance of affordability, strength, and resistance to the challenges presented by venting gas appliances.