With Offsets or Without

[M7mahoney]

I have a decision on how to run thee chimney pipe in the attic. I can offset it about 38" so it will be within 1ft of the peak giving me only 36" above the roof line or I can run it straight up and have closer to 65" above the roof line.

So my questions... What's the lesser of two evils? Straight up and out is best for venting and is cheaper but requires bracing and a snow wedge. Offsetting it will look better and be more secure but have two 45s.

 

[webby3650]

I have a decision on how to run thee chimney pipe in the attic. I can offset it about 38" so it will be within 1ft of the peak giving me only 36" above the roof line or I can run it straight up and have closer to 65" above the roof line.

So my questions... What's the lesser of two evils? Straight up and out is best for venting and is cheaper but requires bracing and a snow wedge. Offsetting it will look better and be more secure but have two 45s.

It would be 30 degree elbows. You sure you can offset 38” at 30 degrees off of vertical?

 

[M7mahoney]

Offset chart for excel had 45 degree with a 48" length, they had 30 degree too, just more rise and w piece connection. Anyhow, better to go straight up or have the offsets?

 

[ABMax24]

Straight up. Easier cleaning and better draft.

 

[webby3650]

Offset chart for excel had 45 degree with a 48" length, they had 30 degree too, just more rise and w piece connection. Anyhow, better to go straight up or have the offsets?

Class A can’t exceed 30 degrees of offset for wood. Double wall connector pipe can, but not chimney.

 

[begreen]

Offset chart for excel had 45 degree with a 48" length, they had 30 degree too, just more rise and w piece connection. Anyhow, better to go straight up or have the offsets?

That is only for Canada. In the US only 30º elbows are permitted for an offset in chimney pipe. That may still be ok but with a shorter offset.

 

[M7mahoney]

Class Aan’t exceed 30 degrees of offset for wood. Double wall connector pipe can, but not chimney.

Oh, thanks!! Odd they have the 45 offset chart. I think I'm going straight up then. Too many parts to make it happen with the 30s.

 

[peakbagger]

Sorry to go against the tide but in a snow zone I would opt for the 30 degree offsets and ridge exit especially with metal roofs. I have seen far too many damaged or leaking chimneys caused by snow sliding down a roof. I also have seen more than a few weird drafting situations caused by interactions of wind blowing across a roof ridge creating turbulence on the down wind side. Moving air likes to flow in smooth layers if possible, as it approaches the ground it starts to get caught up on irregularities on the ground and these smooth layers start to catch and cause swirls and eddy's. On a windy day after the leaves have fallen you can see the leaves on occasion swirl and jump up in the air. When wind hits a flat sloped roof on the upwind side, it inevitably creates an area of low pressure on the back side of the ridge and there will be "curls" of air that form and create all sorts of odd effects. The farther down on the slope of the roof the stack exits, the more these turbulent zones can cause issues. It the top of the stack sticks up past the ridgepole these turbulent zones are lessened but its still better to have the stack exit as close to the ridge as possible. Note this effect can happen on a grander scale with homes located on the downwind side of hill, wind blowing across the summit can create turbulence well down the downwind side of the slope. Normally once the stove is running and the stack is hot it is not an issue but it can be real PITA to light off a stove.

 

[Wildflush]

offsets have not effected my draft at all. I have about 23 ft of EXCEL class A. Roughly 30” from stove collar, 90 at stove connector to a thru wall thimble. Outside 90 T. 2x 30’s to clear my ridge/gutters and a pair of roof braces to secure the chimney above my roof. Looks good and drafts well.

 

[xman23]

I'm a straight up fan boy. Just works better. Drafts better. Cleans better. As long as you follow the height to the roof rules it normally works fine. Mine extends 10' above the roof with one set of braces.

 

[Wildflush]

I'm a straight up fan boy. Just works better. Drafts better. Cleans better. As long as you follow the height to the roof rules it normally works fine. Mine extends 10' above the roof with one set of braces.

Not all houses allows that install. I have a Cape. No difference in cleaning for my sweep who installed my setup and with my chimney height no decrease in draft at all. If I had a short chimney the bends would effect draft.

 

[kborndale]

In a tall enough chimney bends arent hurting anything. In actuality they can be beneficial as when a chimney is too tall you have too much draft and often have to add a damper.