What Is the Right Height of a Chimney?

How Draft Works

• A chimney operates by drawing smoke and other pollutants upward from a fire. The smoke from an open campfire often tends to roll along the ground, but such behavior is unacceptable indoors. The chimney serves to create a draft, sucking the smoke up and releasing it at a safe height. This draft is increased by the height of the chimney; a tall chimney that extends above all surrounding structures will have the best draft.

Dangers of a Short Chimney

• A short chimney will not have sufficient draw, and as a result may release smoke into your home. Other nearby buildings or levels of your house that are as tall or taller than your chimney can also have an adverse effect on the draw strength, further decreasing the chimney's efficiency. Because smoke contains carbon monoxide and various carcinogens, this is a dangerous situation.

Height by Roof Pitch

• The greater the pitch of your roof, the taller your chimney needs to be. According to the District Surveyors Association, a 10-degree roof needs a 2-foot chimney, while a 20-degree slope requires a chimney nearly 3 feet tall. A slope of 30 degrees requires a chimney no less than 4 feet and 4 inches, while a roof that slopes as much as 40 degrees needs a chimney over 6 feet tall. Any chimney taller than this should have its masonry checked for stability.

The 2-3-10 Rule

• The International Fuel Gas Code presents another method of determining the right height for your chimney, known as the 2-3-10 rule. According to this method, any chimney's base minimum height should be 3 feet on the side that faces the upward slope of the roof. In addition, the chimney should extend 2 feet above any surface within 10 feet of it in any direction. This will prevent any nearby structure from interfering with the chimney's draft.