Is your chimney the right height?

The Chimney Safety Institute of America this week received this query by e-mail from a CSIA Certified Chimney Sweep in regards to a homeowner:

“Just wanted to get your take on this. I’ve been talking with this client for around 2 weeks now about rebuilding his chimney. It comes out of the peak of the house and is 27-28 inches tall – as opposed to 36 inches.”

The sweep also was told that a building inspector said the height of the chimney was acceptable, since the 36-inch requirement wasn’t in existence in the late 1950s, when the house was constructed. 

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Our response: In many parts of country, the termination point – the distance between the chimney top and the roof  – historically had been 24 inches, but 2 feet turned out to be “too short” for many homes in terms of creating insufficient draft and/or resisting wind-induced downdrafts.

 “When a homeowner uses their fireplace, the properly vented chimney flue will carry smoke and the byproducts of combustion up vertically and out the chimney cap,” said Ashley Eldridge, CSIA Education Director. “But with chimney that is too short, the wind could impact or interfere with the exhausting of the chimney. Then you might see problems such as insufficient draft and wind-induced downdrafts, so the homeowner won’t have the optimal experience.”

Video from CSIA’s YouTube page: Codes and chimneys from our CSIA expert

Besides helping with venting, the benefit of the “3-foot” chimney comes from a fire safety perspective; it allows that any hot spark that is carried from the fireplace up through the flue has a better chance to be extinguished before it exits the chimney and comes in contact with the roof.

“The extra distance provides that ember, or spark, an opportunity to cool,” Eldridge said.

We don’t know how many chimneys observe different height lengths, but builders will often use the prescriptive approach – they will build them to code.

In some cases, the chimney needs to be raised even though it has met the building code.

“Codes change as we learn the importance of that change.  Just because they don’t have to change doesn’t mean it isn’t a good idea,” Eldridge said. 

If you are someone who has noticed this as a problem, warm-weather season is a great time to have your chimney inspected to see if cosmetic or functional improvements are necessary. You can use the Chimney Safety Institute of America’s free zip-code finder at csia.org to search for a chimney sweep in your area who can assist you with a diagnosis in addition to the annual inspection that CSIA advocates.

Enjoy your chimney and remember, be safe! Inspect to protect.

— Tom Spalding


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