Class A chimney height above roof Question

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gdk84

Member
Feb 23, 2011
139
New England
In order to "maybe" help my excessive draft issue i am having i am thinking of possibly shortning the 5 ft of class A above my roof line. It is about a foot below the peak of the roof. So my question is, I have to be 10 ft away in all directions and have to have a min of 2 feet sticking above that point... or if im at the peak i have to be 3 ft above that? That is what im understanding of all of this. So if it is the case what is the difference? Or am i missing something...
 
3 feet above the point of penetration and it also must be 2 feet higher than anything within 10 feet of the cap.

If the peak is more than 10 feet away from the cap then you might be able to shorten things. If not, then no.

pen
 
You DO have to abide by the 10-3-2 rule.

Also keep in mind that by shortening your chimney you may introduce some wind induced pressure problems. If you really think you have excessive draft, maybe try a key damper first.
 
So if my pipe sticks out a foot below the peak and i have a 4 ft section above that, can i get away with replacing the 4 ft section with a 2 ft and still meet code?
 
Just curious what is wrong with your draft that you think you have overdraft.
 
cmonSTART said:
You DO have to abide by the 10-3-2 rule.

Also keep in mind that by shortening your chimney you may introduce some wind induced pressure problems. If you really think you have excessive draft, maybe try a key damper first.


My total chimney height is 18 feet. Double wall connector to class A. I do understand that part of it. I do however really dont want to rely on a key damper to keep things in order. For me, i'd rather turn my draft all the way down and have piece of mind and not have to worry about a second adjustment.
 
I'm having a hard time visualizing what you're describing. You have to have at least 3 feet of chimney sticking out, AND it has to be at least 2 feet higher than anything within 10 feet.
 
certified106 said:
Just curious what is wrong with your draft that you think you have overdraft.

Outside of my double wall 400 plus with stove air completely shut, stove top hitting over 800 with air shut... Makes you wonder, and semi seasoned wood to boot.
 
cmonSTART said:
I'm having a hard time visualizing what you're describing. You have to have at least 3 feet of chimney sticking out, AND it has to be at least 2 feet higher than anything within 10 feet.

If you measure from the peak to where my chimney is, in vertical distance, is 12 inches. I have a 4 ft section of class A above that. So basically, the bottom of the 4 ft section is at the peak level. If i remove the 4 ft section and replace it with a 2 ft section than i should still be within code, i hope, since nothing around it is within 10 ft and it sticks out 3 ft from penetrating the roof.
 
gdk84 said:
certified106 said:
Just curious what is wrong with your draft that you think you have overdraft.

Outside of my double wall 400 plus with stove air completely shut, stove top hitting over 800 with air shut... Makes you wonder, and semi seasoned wood to boot.

Yikes that's pretty high. Im sure you already checked to make sure the ash door and front door are sealing.
 
I did indeed check that. I dont have a ash pan but i did check the door and also consulted with my dealer.
 
Should not be over drafting with only 18ft of chimney. Stoves are typically tested with 12-14ft, so I cannot see another 4ft making that huge of a difference.

Maybe you need to close the air down sooner in your burn, if left open too long sometimes the fire gets to a point where you can no longer control it properly. Also check all the gasketing and any other place air could leak into the firebox.
 
Fix the stove leak. Placing a bright light in the stove you may be able to see a leak. Or running a lit cigarette slowly near the door and store joints.
 
gdk84 said:
cmonSTART said:
I'm having a hard time visualizing what you're describing. You have to have at least 3 feet of chimney sticking out, AND it has to be at least 2 feet higher than anything within 10 feet.

If you measure from the peak to where my chimney is, in vertical distance, is 12 inches. I have a 4 ft section of class A above that. So basically, the bottom of the 4 ft section is at the peak level. If i remove the 4 ft section and replace it with a 2 ft section than i should still be within code, i hope, since nothing around it is within 10 ft and it sticks out 3 ft from penetrating the roof.

My interpretation is that you would not meet the code requirement on two points.

1. You'd be too short for the 2' clearance above the ridge line, by the distance in eleveation between your roof penetration point and the roof peak. How short depends on your roof pitch, and would be merely inches on even the steepest pitch, but you would be short nonetheless.

2. If your last pipe section joins close to, or even with, the roof decking, you violate the 3' minimum exposed pipe rule.
 
One other point, just an FYI on this general subject, more than anything. When I was calculating my class A length I talked to a stove dealer who said the minimum length is calculated by the stove manufacturer using the BOTTOM of the firebox as the starting point, not the connector exit at the top of the stove. When you think about it, that does make sense.

I'm also of the mind that you need to check for air leaks on your stove, rather than re-engineer your chimney. A few feet less of draft is not likely to be the crucial factor here. Work from the bottom up on over-draft issues, I believe.
 
I'd definately be going over the stove w/ a fine tooth comb. Other factors could be split size and wood variety. If these are fairly small splits and soft wood to boot, that could be your problem alone.

However, since you chimney is to spec now, after you prove the stove's integrity my advice would be to refer back to what cmmonstart said and try installing a key damper at a cost of about 10 bucks.

pen
 
I just added a 4 foot of class A to my stove so it would meet code requirements, I can tell you it really woke up my stove, but it is still very controllable! I was running 12 feet of A, and about 4 feet of double wall.
 
I figured 4 ft wouuld def make some differenve on draft. I have heard that the EPA tests done on my model was something like a 10 ft chimney at 75F temp or something like that, so when it sees a 18 ft or more chimney double wall through the center of the home where the pipe isn't cold you bet the thing drafts like crazy when its zero outside. Almost too crazy for my liking, and it isn't the stove I can tell you that much. Plus, it all depends on your location. Someone may have a 25 ft chimney and be fine just different location. Did you notice any reduction in burn times when you added the 4 ft?
 
No, but I haven't burnt it much yet. The season is winding down here, and we have just been running the pellet stove...and getting next years wood supply in.
 
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