cathedral ceiling chimney installation

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disamatic

disamatic

New Member
Aug 6, 2014
80
Gold Bar Washington
Hello folks, hope all is well. So I am getting ready to start my chimney install, but am a bit confused, I have a sloped ceiling in the house and same on the roof, the gap between the attic and the roof is approximately 3'. Do they make a cathedral box that tall? I am confused, I just want to follow code and have this be right. Any help would be greatly appreciated. Thanks fir your time.
 
Dura-vent makes a 36" box. But there is no real reason to use it, its really for super steep ceilings.

You just run your box up above your rafters, and let it hang down into the room a few inches below the ceiling on the low side. Then put an attic insulation shield on top of the box.
If you have no attic access the. You can do this. So get a box that is tall enough to go above your insulation.
 
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webby3650 said:
Dura-vent makes a 36" box. But there is no real reason to use it, its really for super steep ceilings.

You just run your box up above your rafters, and let it hang down into the room a few inches below the ceiling on the low side. Then put an attic insulation shield on top of the box.
If you have no attic access the. You can do this. So get a box that is tall enough to go above your insulation.
Click to expand...


Hey thanks for the reply, yes i have attic access, I purchased a supervent JSC6CCSB support box, it is 17 1/2" tall. So what your saying is to mount the box with the necessary amount below the sheet rock and build a box around the rest of it? All the way to the roof sheathing?
 
disamatic said:
Hey thanks for the reply, yes i have attic access, I purchased a supervent JSC6CCSB support box, it is 17 1/2" tall. So what your saying is to mount the box with the necessary amount below the sheet rock and build a box around the rest of it? All the way to the roof sheathing?
Click to expand...
No, you need to buy an attic insulation shield. It goes ontop of the box to prevent insulation and other junk from falling down into the support box.
There is no reason for the pipe to be boxed in all the way through the attic.
 
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Ok, i purchased one of those as well, so your saying use a cathedral support that is taller than the insulation, then put the insulation shield on top of the box, and as long as the exposed double wall is above the insulation line it should be fine? Sorry i am not super educated, if i had a flat cieling it would be much easier, the scissor truss situation seems a bit tougher.
 
Just run that box up as high as you can. Then use the shield ontop of the box, anything exposed above that is fine.
 
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webby3650 said:
Just run that box up as high as you can. Then use the shield ontop of the box, anything exposed above that is fine.
Click to expand...
Well this sounds ok, but I got home from work and took the box and the attic insulation shield and put the shield on top of the box, seems odd, do you make framing to hold this together? Do you just screw the shield to the box? I think it will work, but is this a common solution? I'm not doubting your knowledge just trying to feel it out a bit more. Thanks.
 
it usually screws to framing but in your case you would screw it to the support box
 
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as long as the insulation shield is there and it keeps he insulation away. And there is nothing combustible within the 2" clearance that part should be ok. Follow the directions and you will be fine as far as codes go.
 
Disamatic, there are instructions that come with the box to show you how to do it, the main issue is to keep insulation / debris from falling in the box, the box is designed to hold the chimney pipe (triple wall) in center while maintaining the proper clearance from the sides of the metal box framing, the insulation shield goes around the triple wall above the box and slides down to cover the open top sides of the box therefore keeping objects out of it. after that you will need the thru the roof kit, that part is what goes in the shingles and supports the top of the chimney from side to side movement. If you have a lot more questions or feel uncomfortable with installing this please don't take a chance and call a certified chimney sweep.
 
bholler said:
as long as the insulation shield is there and it keeps he insulation away. And there is nothing combustible within the 2" clearance that part should be ok. Follow the directions and you will be fine as far as codes go.
Click to expand...
Ok, that sounds good, I may be over thinking this a bit, but just want to be safe, my insulation shield is aselkirk retro fit style 2 piece, plus the collar that goes over the top, so I am thinking I can attach the halves, set on top, relief cut the corners and fold down and attach to the support with machine screws. And the rest is looking pretty easy.
 

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kennyp2339 said:
Disamatic, there are instructions that come with the box to show you how to do it, the main issue is to keep insulation / debris from falling in the box, the box is designed to hold the chimney pipe (triple wall) in center while maintaining the proper clearance from the sides of the metal box framing, the insulation shield goes around the triple wall above the box and slides down to cover the open top sides of the box therefore keeping objects out of it. after that you will need the thru the roof kit, that part is what goes in the shingles and supports the top of the chimney from side to side movement. If you have a lot more questions or feel uncomfortable with installing this please don't take a chance and call a certified chimney sweep.
Click to expand...
Yes I found the instructions in the box, they do not illustrate my scenario at all. They don't illustrate or explain what should be done when there is that much of a air gap, I have no fear of this job, I won't compete the job until I am 100% comfortable in doing so. With that said, it sounds like I have 2 options, either the very tall box that would attach to the roof, or the option we are discussing now with the shorter box and the insulation shield. And I am using double wall pipe.
 
Yeah lots of people call it triple wall i am not sure why you can do it with what you have there no problem. Just put your box in according to the instructions then attach the insulation shield to the top of that box some how. You can bend it like you said that is what i would do or use ange brackets you could even use wood as long as it is outside that box.
 
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bholler said:
Yeah lots of people call it triple wall i am not sure why you can do it with what you have there no problem. Just put your box in according to the instructions then attach the insulation shield to the top of that box some how. You can bend it like you said that is what i would do or use ange brackets you could even use wood as long as it is outside that box.
Click to expand...
Thanks bholler, sounds like a plan, appreciate your thoughts and help. I will post some pictures when complete!
 
bholler said:
Yeah lots of people call it triple wall i am not sure why you can do it with what you have there no problem. Just put your box in according to the instructions then attach the insulation shield to the top of that box some how. You can bend it like you said that is what i would do or use ange brackets you could even use wood as long as it is outside that box.
Click to expand...


Never heard anyone call class A double wall chimney, triple wall unless it was air cooled triple wall chimney pipe made for a fireplace........
 
Rickb said:
Never heard anyone call class A double wall chimney, triple wall unless it was air cooled triple wall chimney pipe made for a fireplace........
Click to expand...

I hear it all the time some even on this site. That and i also hear it called stove pipe allot to i don't see that here at least. But even calling it double wall is not right because double wall is a totally different product used for a very different application.
 
Rickb said:
Never heard anyone call class A double wall chimney, triple wall unless it was air cooled triple wall chimney pipe made for a fireplace........
Click to expand...
For some reason the majority of people call any metal chimney triple wall. They just don't know, that's all. Triple wall is air cooled pipe, but it was made for wood stove flues as well as fireplaces. The majority of it was only rated for 1700 degrees, but later insulation was added that made it good for 2100 degrees, Like modern class a pipe.
 
Yes and it generally has lots of creosote in it because it is cooled which is the opposite of what you want for performance.
 
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