*** The CHIMNEY CAP thread ****

[Gooserider]

I would certantly have separation distance above flues making it less of a down draft pulling down smoke from the stove exit into an adjacent flue

thanks for bringing up this post it ties in with the ZC liner post discussion

One that I have been wondering about, and currently seem to have "wrong" in my install is what happens with multi-flue chimneys - Elk says there is supposed to be a height difference between the two stacks, but I also see that 10-3-2 rule saying that the flue exit needs to be above any nearby obstacles. Given that in a multi-flue chimney, the different flues are only going to be about 4" away from each other how does this work? As I see it the 10-3-2 rule would say that as soon as you raised one flue at all above the other, you would need the lower one to be extended to be 2 feet taller than the first and vice versa... :-S Is this an exemption to 10-3-2 or what? Also if one is making the flues different heights, does it matter which one is taller, and if so, how do you decide...

Right now I have two flues in my chimney, one for each stove, both at the same height, and covered by a common cap.

Gooserider

 

[webbie]

From a code point of view, most everything is a circular reference.....like the error message you get when you type the wrong formulas into Excel - in other words, if we take each part of the code and standards and operating instructions word-for-word, just about nothing is legal! It's very confusing, which is why intelligent human beings will never be replaced by computers in certain occupations (building officials and stove installers are two examples).

http://en.wikipedia.org/wiki/Circular_reference
"A circular reference, or sometimes known as a run-around by some people, is a series of references where the last object references the first, thus causing the whole series of references to be unusable."

I could not have said it better!

In terms of chimney caps for class A chimneys, we have been through this before and the stock caps are usually the best caps. Despite claims to the contrary, many draft increasing caps simply don't work. Also, it is proven that using a cap actually HELPS the chimney in most situations, as opposed to the theory that NO cap is better.

Back to the real world, it is often required for unlisted caps to be installed because a manufacturer (Preway, etc.) has long since gone out of business and the factory cap is rusted out. In these case, I would say the following guidelines apply:
1. If the chimney is solid-packed or single wall stainless liner, any cap with a decent sized open area would do the job.
2. If the chimney is air-cooled, attempt to find the manufacturers replacement cap. If you cannot find original replacement, discuss the situation with experts such as the folks at ICP (makers of Vacu-Stack and other products) - they know the issues at hand and make special air-cooled replacement caps.

BTW, here is the wiki article with the research that proves the positive functions of "regular" caps:
https://www.hearth.com/econtent/index.php/wiki/Effect_of_wind_on_chimney_caps/

 

[webbie]

Goose, the deal about varying flue heights is not actual written code, but more of a "standard" written by the Masonry Institute. It is also currently referenced in some of the education materials written by HPBA as well as in materials produced by HUD.

From MIA:
"5.17, Masonry Institute of America - "The pouring of smoke from one flue to an adjacent flue occurs where downdraft from interior suction or vertical wind currents force smoke down an inactive flue as it exhausts from the adjoing flue"
5.14, Masonry Institute of America "The top of a flue should have a height differential...as much as 12 inches to prevent smoke from pouring from one flue into the other flue"

Also see:
http://www.extendacap.com/images/mia1.gif
http://www.extendacap.com/images/mia2.gif

 

[jqgs214]

Goose, I have the same setup as you except my second flue is from my furnace/boiler. I have not experience any issue with it "yet". My 2 sweeps that I have used so far have not had any issues and I did pose the question to them. One said that I can be a problem when the chimney although following the 10-3-2 rule does not extend above the ridge. I dunno bout that but mine is staying this way for now.

 

[Gooserider]

Goose, the deal about varying flue heights is not actual written code, but more of a "standard" written by the Masonry Institute. It is also currently referenced in some of the education materials written by HPBA as well as in materials produced by HUD.

From MIA:
"5.17, Masonry Institute of America - "The pouring of smoke from one flue to an adjacent flue occurs where downdraft from interior suction or vertical wind currents force smoke down an inactive flue as it exhausts from the adjoing flue"
5.14, Masonry Institute of America "The top of a flue should have a height differential...as much as 12 inches to prevent smoke from pouring from one flue into the other flue"

Also see:
http://www.extendacap.com/images/mia1.gif
http://www.extendacap.com/images/mia2.gif

Ahh... The second reference did give the answer to the question of which flue should be higher if putting in a difference - the appliance that is highest in the structure should get the tallest flue. It is still an item of the code that I'm surprised doesn't get addressed more - I've never seen a stove manual that deals with anything other than a single flue chimney.

Gooserider