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wood stove vent pipe install- clearance question

nakman

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Quick question when installing a 6" double wall vent pipe. How much oversize should I cut the hole in the roof? was thinking 1" all around.. or thereabouts. Can't seem to find a good answer anywhere on the internet.

here are some pics, all opinions welcome! :beer:
 

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nakman

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Or do I frame in a box the size of the metal roof flange thing?
 

DaveInDenver

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FWIW, I used double wall from the stove connector to the ceiling support and it was triple wall insulated (class-A) chimney pipe from there to the roof sheathing collar and cap. The actual chimney technically started at my ceiling, so I have the big box right there.

IIRC Larimer County wanted to see 2" or maybe it was 3" from the blocking and sheathing in the roof to the chimney pipe. I can't find the building code reference right now, but as I recall Larimer didn't take any exception to the 2009 Code, which was in effect at the time. But, yes, there was a framed in box around the flue-chimney at the ceiling above the stove and a framed box around the collar at the roof. That's where the inspector took the distance measurements.

It looks like this at the roof jack, big collar, storm flashing over it.
Storm-Collar.jpg


I had to use double wall inside because they needed 18" minimum clearance for single wall to combustible material, which was violated by a partial divider wall in our room. With double wall the clearance was 6".

But I was going through an attic with insulation and did it by the book with an inspection, so my requirements were a little different.

ETA: If you were to take off the drywall on the ceiling over my stove this is what it would look like, with some blocking around the roof jack:
support-box.jpg
 
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nakman

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Ok thanks Dave for the input I think I will just build a box in the roof then to support the big flange on top, that way I'll have 3" all the way around the pipe. Requires me to scoot the stove over a little, but no big deal.. Just have to remember not to stand there when doing the roofing.

What kind of stove are you installing? It's an important question.

Making one from a 55 gallon barrel.. so not exactly UL certified but at least the fire won't start in the ceiling now. :eek:
 

DaveInDenver

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I bought a manufactured stove so I dunno if it would be any less PITA. I don't think they were worried about the stove itself as long as you adhered to the clearances. I think it was 36" to any combustible or 18" with protection, be it tile or using double wall pipe.

They were very concerned about the chimney and there are different requirements for solid fuels like wood vs. liquid or gas stoves.

FWIW, some of the applicable codes are UL 1777 and NFPA 211. The building code here is ICC IBC (2009 at the time).

If memory serves the chimney cost as much as the stove, it was pretty involved.
 

DanS

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Dave has it right. Barry linked the clearances.

Basically just install the box, and that will provide the clearances you need. If you haven't purchased one yet, buy the support box that matches the stovepipe you are using. I buy them at the same time, just to make sure.

And yeah, it's pricey. I have over $1100 in the support box to the top of the chimney into mine, and I still have to do some metal fabricating (luckily--I do that!) to support the box (since it's not just going through a stick frame structure).

I like McGuckins (even with the change in ownership) for stove stuff. They will let you look at all the bits, and have a couple demo installations so you can see how to install them.

Dan
 

nakman

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Ok this feels a lot more legit now, thanks guys. :beer:
 

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rover67

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To one of those drip collars over the pipe above the flashing and use some stuff to seal it. What’s it going in? Another shed in South Park?
 

rover67

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Also if it’s double walled but not insulated which I’m guessing it’s not it’ll still get hot. Double check it when u burn to see how hot that wood and stuff is getting.
 

DaveInDenver

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Also if it’s double walled but not insulated which I’m guessing it’s not it’ll still get hot. Double check it when u burn to see how hot that wood and stuff is getting.
This is true, Class A chimney pipe is either insulated double or has two air gaps. The really Cadillac triple wall stuff will have an insulated layer and an air gap.

This is for two reasons. The first is obviously to keep the pipe cool on the outside but still keep the inner most layer hot. If it doesn't stay hot up you get a weak draft and it encourages creosote build up.

It really is a rabbit hole, I had no idea when I started out.

That roof jack looks good. You do need a storm collar over it, like in the photo in an earlier post.
 

60wag

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My old gas fireplace drew the intake air down the outer pipe space and the hot exhaust went up the inner space. This kept the outside wall of the pipe cool to the touch.
 

nakman

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Yeah I got the little collar deal, just didn't have it on for the pic.. and the pipe definitely gets hot, I put a thermometer on it, it's in the 300-400 F range.. which according to the thermometer, is "best operation." :)

imgCache-TemperatureGauge_640_0.jpg
 
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