Roof pitch rise run in inches.
B vent height above roof.
1 5 feet above the roof surface.
Above the roof plumbing vent height.
Metal bracket on a b type vent metal chimney.
One of the fire safety features of double wall type b gas vent is that its outer wall insulated by the airspace beneath it requires only 1 clearance to combustible material in the structure.
The clearance required from combustible materials is printed on the flue s exterior metal surface and is generally 1 or 2 inches.
Vent pipes should extend to outdoors above the building roof and should terminate vertically not less than 6 above the roof surface nor more than 24 and must be at least 12 from any vertical surface such as a nearby sidewall.
Minimum height above the roof surface 1 flat to 7 12.
2 5 feet above the roof surface.
Although a large portion of the flue gas is composed of water vapor amerivent type b gas vent carries it out of the structure before it can condense.
Per the 10 and 2 rule once you are at the level of the peak you only need to be 2 feet above it.
So 28 inches plus 24 inches is a chimney height of only 52 inches.
Table of rooftop chimney clearances for metal b vent chimneys flues.
Photo at above left.
This reduces the actual required height by 12 inches from our previous calculation of 64 inches.
The 1992 vent sizing tables require that all type b gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer s instructions.
However b vent chimney caps 12 and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as given in this table.
7 14 4 a chimney shall extend not less than 3 ft 900 mm above the highest point where it passes through the roof of a building and not less than 2 ft 600 mm higher than any portion of a building within a horizontal distance of 10 ft 3 m.
If the cap is damaged or lost it should not be substituted with something not recommended by the manufacturer.
In the case of type b or type l vents each length extending above the roof line must be certified for exterior use and so identified.
Type b vents must be equipped with their own special chimney caps.
Notice that metallic salts washing off of the metal bracing and other runout of the chimney flashing itself are preventing black algae from growing on some areas of this roof.
2 0 feet above the roof surface.
