Type B and Type L Vent Inspection
- wood-burning appliances, such as fireplaces and wood-burning stoves;
- oil-fired equipment;
- coal-fired equipment;
- any appliance that burns anything other than liquid petroleum or natural gas; or
- any appliance that produces flue gasses that exceed 480° F (249° C).
Type B vents must be equipped with their own special chimney caps. If the cap is damaged or lost, it should not be substituted with something not recommended by the manufacturer. The clearance required from combustible materials is printed on the flue’s exterior metal surface, and is generally 1 or 2 inches.
- deterioration of the outer wall, which is likely caused by failure of the inner metal lining;
- violation of roof clearance requirements. All metal vents must terminate at least 2 feet above the roof surface and anything within 10 feet of the vent, such as the crest of a roof ridge;
- missing components, such as a chimney cap;
- firestops not installed at either the top or bottom side of the joist where the vent passes through floors or the roof. The firestop should allow a fire-resistance rating equal to or greater than the floor or roof assemblies through which the vent passes;
- blocked bird screens, often caused by freezing moisture in cooler climates;
- crucial joists, rafters or other load-bearing structural members that have been cut to allow for the vent to pass. Plumbing and electrical lines should also not be disturbed by the vent; and
- whether the vent is too high or too low. Manufacturers may set minimum and maximum height requirements for the whole vent assembly, such as the AirJet Type L vent, whose minimum height is 6 feet and maximum height is 30 feet.