Chimney height for short cabin

[Alexander L]

Hi all! have two quick questions about my stove install.

I am installing a Jotul F100 in my small cabin. The roof is a flat-ish top gambrel style... so the cabin is not very tall.
I purchased four lengths of 36" chimney pipe that measure 11' 7" (combined) in heigh above the tee (I am installing out the back of the stove through the wall into a thimble and tee.

Question 1) The 11' 7" of chimney (above tee) will clear the roof peak by about 3 1/2 feet. Enough to satisfy code... but is this really enough chimney length for a proper draft? This is my first stove, so please excuse my newbie-ness. I can pick up another 24" or 36" length of chimney in the next town, if necessary.

Question 2) Is it necessary (by code) to have any amount of rise in the horizontal run of black stove pipe that is exiting the back of a stove and running horizontal into the wall thimble? There is nothing in the instructions about a this, but I read somewhere in a hearth post that this is necessary? The distance from the rear of the stove to the wall thimble is only about 9 inches... so not much pipe . The instructions (Duraplus) call for the thimble to be centered at the same measurement as the center of the rear exit on the stove. Nothing about any rise when going horizontal.

Appreciate any advice!
Here is a pic of the stove room:

 

[begreen]

11'7" is short for this stove, another 36" would help, but that may need a roof brace.

Ideally a 1/4"/ ft rise is advisable for the horizontal section, but in a 9" section that would be hard to achieve.

 

[Alexander L]

Thanks, begreen.
I had a feeling another 2 or 3 feet of chimney would be needed. I already plan to use a roof brace, as the short walls only allow for one wall brace. Mostly steep pitched roof.

I'll have to ask my local about what he wants to see regarding a 1/4"/ft rise on that short bit of horizontal from the stove. Will matter to the wall thimble height.

 

[Alexander L]

Related to the chimney height...

If I add another 3 foot section of chimney pipe, total height becomes 14.5 feet of chimney above the tee. Doing so will put my chimney at about 6 feet above the tallest point of the roof (center peak). This is roughly 12.5 feet of freestanding chimney pipe above that wall bracket where roof meets wall. That seems like a lot of pipe in the air.

Duraplus install calls for:
"If the chimney extends more than 4 feet above the roof line, an Extended Roof Bracket must be installed at every 4-foot increment of height above the roof line, leaving no more than 4 feet extending above the last pipe band."

So, were are talking minimum of two roof brackets installed to keep this much freestanding chimney braced,satisying the install direction. Correct?

Illustration for understanding:

 

[begreen]

Yes, that is an awkward install. I probably would put the middle brace sloping upward at ~45º from the middle of the roof slope.

Is relocating the stove and going straight up is an option?

 

[Woody Stover]

What is the altitude of the cabin?

Is relocating the stove and going straight up is an option?

I wondered if he could run the chimney inside and hide it but I think clearances might be an issue even using class A chimney. Inside pipe is gonna be the elephant in the room in that small a space..

 

[Woody Stover]

White chimney?

 

[begreen]

What is the altitude of the cabin?
I wondered if he could run the chimney inside and hide it but I think clearances might be an issue even using class A chimney. Inside pipe is gonna be the elephant in the room in that small a space..

Not really. It's done all the time with cathedral ceilings.

 

[SuperJ]

Straight up would be nice and clean looking, and you'd get the added advantage being able to use cheaper doublewall inside, and taking advantage of the heat radiated off the stove pipe into the cabin, instead of outside.
The effective height would be greater too, since you elminate 2 90's.

You might need to offset to get to the flat roof, but that can be done pretty tidily closer to the ceiling.

 

[Alexander L]

Yes, BG, an akward install... but I decided to go out the back because, as Woody points out, the room is so small that going straight up would likely mean that the stove would have to come further out into the room to satisfy clearances. The room is 11 feet wide, wall to wall. Those side walls are about 4 feet tall before they reach the T&G roof. Other side of this room is my small kitchen. Not many places in the room to put the stove.

Not sure what kind of angles/elbows would be needed to get the upward stove pipe(black) away from the T&G (combustibles) without coming too far into the space. The top of the roof is torch down bitumen membrane, as it is too flat for shingle. I figured that would require a roofer to torch a patch over a roof flashing for waterproofing a roof penetration.

Here are some pics for further view of clearances/ceiling pitch:

 

[Woody Stover]

Not really. It's done all the time with cathedral ceilings.

Looking closer, looks like a hunting cabin so appearance probably won't be high priority. I would sure want to keep the chimney inside and go out the roof if I was trying to get good performance out of a short chimney..

 

[begreen]

If interior, it looks like with double-wall connector pipe that it would come up about 3-4', then a 15 or 30º elbow, following the slope of the roof about a foot away, then another 15 or 30º elbow to return to straight up. Or maybe relocate the stove to the end in front of the windows and move the sideboy to the stove location.

Flat roof discussion here:
https://www.hearth.com/talk/threads/flat-roof-install-what-chimney-support-should-i-use.41090/

 

[RobbieB]

I like that idea. Yeah double wall pipe and parallel the T&G and go right through the top.

 

[Alexander L]

Great ideas and info! Thank you.
Hmmm... I already own 4 lengths of 36" stainless Duraplus chimney pipe and the thimble with associated parts to go through the wall. Too late to return any of that stuff. Bought it a while back.

I really figured that running double wall parallel to the T&G and into a ceiling box would have pipe a bit too far into the room, possibly right at head height when walking by. I will have to go up and have a close look at the angles and clearances.

But going out the back into a thimble... I am still all good with 5 lengths of 36" pipe above the tee so as long as it is properly supported with roof braces?

 

[RobbieB]

Try it and see I guess. If you don't have draft problems you're good. If you do the inside pipe method will draw much better.