What type of gas vent is typically used for Category III appliances?

Category III appliances are designed to operate with non-condensing gas and typically use a venting system that allows for the discharge of flue gases at higher temperatures without the risk of condensate forming. The correct type of vent for these appliances is Type B vent. Type B venting systems are specifically constructed for venting appliances that produce flue gases that are at a temperature greater than the dew point, which is essential for Category III appliances to ensure safe and efficient venting.

Type B vents are built to be more lightweight and often have a double-walled construction that provides insulation to maintain the temperature of the gases as they rise, preventing the formation of condensate. This feature is crucial, as condensate can lead to corrosion and damage to the venting system and surrounding structure.

In contrast, other types of vents such as Type L and Type PL are designed for other applications, including those that may involve condensing or are used for different categories of appliances. Type K vents typically represent special high-temperature situations not commonly associated directly with the typical venting needs of Category III appliances. Thus, Type B is the most suitable and safe choice for ensuring proper venting of flue gases for Category III appliances.