Fireplace B-Vent Requirements

Height

• The top of the B-vent will extend past the top of the roof. To avoid sparks from the top of the vent from catching the roof on fire, allow at least 3 feet between the top of the roof and the vent outlet. Any part of the roof within 10 feet of the vent needs to be at least 2 feet lower than the top of the vent.

Material

• B-vents are double-walled flue pipes. Galvanized metal on the outside protects from the elements. An air gap between the inner and outer layers insulates to keep the heat from the vent from affecting outside structures. The interior is made of aluminum for its lightweight and flexibility.

Damper

• Some vents have dampers in them to protect against animals or rain from falling down the vent and entering the fireplace. When using a fireplace, this damper must remain open to provide enough oxygen for the fire to burn. Some B-vents have automatic dampers that open and close based on whether the fireplace is lit or not. This is not a requirement, but it is a useful option if you forget to close the damper.

Use

• B-vents are used with gas fireplaces that do not require direct venting. Metal construction prevents corrosion in the vent from the byproducts of burning gas, but you cannot use B-vent fireplaces in every room of the house. Some municipalities prohibit their use in small, enclosed areas such as bathrooms, bedrooms and sitting rooms. For such places, you might need a direct vent fireplace, which will have closed doors on the front to prevent drawing too much oxygen from the room.