A Properly Constructed Chimney
By Doug Hetsch
June 9, 2015
Not every home builder knows the exact specifications of a properly built chimney, and we at All American Chimney Services, LLC have seen many poorly constructed chimneys in our years of business. Not only do we provide masonry chimney repair services, but we also can rebuild badly built chimneys so that they can function properly and safely. We would like to tell you more about what goes into constructing a chimney in accordance with the standards set by theNational Fire Protection Associationin its Standard 211 for chimneys, fireplaces, vents, and solid fuel-burning appliances.
Most local building codes have adopted many of the standards set by the NFPA 211, and these standards include the following:
For fire safety reasons, the minimum height for a chimney is the greater of three feet above the highest point where the chimney meets the roof or two feet higher than any part of the structure or adjoining structures within 10 feet of the chimney.
CHIMNEY FLUE SPECIFICATIONS
The shape and size of the chimney flue cannot change within six inches above or below any point where the chimney passes through a combustible floor, ceiling, or roof.
MASONRY AND WALL THICKNESS
Any chimney that penetrates through the wall thimble must have a minimum of eight inches of masonry and 12 inches total distance away from anything combustible. All residential masonry chimney wall thickness should be a nominal four inches.
All masonry chimneys should be properly lined with material appropriate for the level of chimney service and the type of appliance to it in accordance with the manufacturer’s guidelines and specifications.
CHIMNEY CLEARANCE GUIDELINES
Chimney clearance from combustible material is a minimum of two inches except where the chimney is located outside the structure. In that case, one inch is acceptable. The through wall thimble is especially important because it can get extremely hot and should be carefully addressed.
Flues can be built to discharge their byproducts of combustion with other flues as long as the flues do not slope more than 30 degrees from vertical. Also, the flues must be expelling byproducts of similar fuels. For example, you cannot combine a flue of a wood-burning fireplace with the flue of a gas-operated heating appliance. Lastly, the main discharge flue should be sized for the maximum combined flow of both smaller flues.
Have questions about a properly constructed chimney? ContactAll American Chimney Services, LLCto find out more information about this important topic.