How High & Long Can a Chimney Be?

Draft

• A taller chimney is more effective than a shorter chimney in most instances. Taller chimneys have a better draft -- the air current that draws smoke and fumes out of the house -- than comparable short chimneys. One advantage of a taller chimney is that you can adjust its draft more easily than you can with a short chimney. A tall chimney with too strong of a draft can be adjusted with a damper, but a shorter chimney might need a complex repair to achieve the same result.

Exposed Portion

• Although building codes typically don't regulate the absolute height of a chimney, they do address the issue of the portion of the chimney that extends through the roof. The exposed portion must reach at least 3 feet above the roof line. It must also be at least 2 feet higher than any object within a radius of 10 feet. The purpose of these regulations is to ensure that the chimney is not subjected to air turbulence from the wind caused by nearby objects.

15 Feet

• As a general rule chimneys work best when they have a height of at least 15 feet from the floor where where the fireplace or appliance sits to the end of chimney top above the roof line. When a chimney shorter than this exists, problems can develop. A chimney well under 15 feet may become a fire hazard due to improper venting. It can also cost you money by forcing a wood stove or oil burner to use more fuel.

Type-B

• Type-B vents -- metal chimneys often used to draw smoke from gas appliances with hoods -- should conform to certain height regulations for proper functioning. The vent should extend at least 2 feet above any object within 10 feet of the vent. The vent top should also reach at least 2 feet higher than any objects within a 10-foot radius. The minimum height of a type-B vent above the roof depends on the size of the vent's cap, the roof pitch and whether the vent is 8 feet or more away from a vertical surface.