Simple Chimney Question

[Stephen D. Schroetke]

What is the purpose of the 2/10 requirement for chimney height. I've asked my fire cheif and he wasn't sure though we have a couple of guesses.

[Bob Elliott]

Back drafting

[Nick Gromicko]

Correct. 17.8.5.3 http://www.nachi.org/comsop.htm#17

Inspection reporting form in there too.

[Stephen D. Schroetke]

Thanks guy's. I actually thought it was to prevent smoke from entering the attic through the roof vents.

[Marcel Gratton]

Originally Posted by sschroetke

What is the purpose of the 2/10 requirement for chimney height. I've asked my fire chief and he wasn't sure though we have a couple of guesses.

For proper draft!

Your fire chief should also known the difference between ionization and photoelectric technology in smoke detector's and the purpose of CO detectors.

Unfortunately most don't...

[Larry D. Kage]

Originally Posted by mgratton

For proper draft!

That's right, Marcel...

[Tim Larsen]

Originally Posted by mgratton

For proper draft!

Your fire chief should also known the difference between ionization and photoelectric technology in smoke detector's and the purpose of CO detectors.

Unfortunately most don't...

Actually, another way to put that is that it prevents down drafts caused by wind coming over roof peaks, etc.

Tim

[Kenton H. Shepard, CMI]

To put it simply...

Wind blowing across the chimney opening helps draw exhaust gasses from the exhaust flue. If you were to look at it on a really small scale, you'd see that the wind creates a vacuum across the top of the chimney. This helps to suck gasses out of the chimney.

If the roof shape interrupts the flow of the wind, it reduces the pull that the wind has on exhaust gasses.

The chimney needs to stick up high enough that the wind blows across its opening. If it's too low... it won't work well.

[Brian A. MacNeish]

[quote=sschroetke;591859]What is the purpose of the 2/10 requirement for chimney height. [quote]

The 2/10 rule is a code minimum and make not work in some extreme sitiuations such as when a house is surrounded by higher coniferous trees and the chimney is in the lee of the prevailing winter winds coming over the trees and then moving downward. Another situation is when the 2/10 rule is met and the chimney exits a low roof in the lee of a higher roof's prevailing winds.