Help with Supervent install

[BamaRama]

The instructions say "NOTE: When a suspended ceiling is encountered a Cathedral Ceiling
Support Box is to be installed. Secure the Cathedral Ceiling Support Box to the floor/ceiling joist framed on all 4 sides. The box must extend a minimum of 1" into the room below the suspended ceiling. Chimney
Length is to protrude a minimum of 3" below support. Trim angles must be installed.

I'm making a suspended ceiling on the back wall and behind a decorative open beam. The bottom of the beam is 2" below the suspended ceiling. The bottom of the dropped ceiling is 56" below the 12/12 roof peak.

So I envision the 17.5" tall box extending 1" below the finished ceiling, then the pipe protruding some distance (3"?) below the beam. Am I on track here?

The Supervent install instruction is not clear that an attic insulation shield will fit/should be used with the cathedral box. It sort of implies it, but never says it specifically. I have the space and then some to get it on there. I don't want to order the parts if it's not going to fit / not to specs. Duratech has the same setup as I'm describing in their literature, but their pipe is pricey, so I'm trying to find another option.

Pic should clarify where I'm trying to go with this. I'm offsetting from center to avoid the peak. There is an attic space above the finished sheet rock. I'm not through framing yet, I stuck the 2x6 frame up there to decide if it will be doable.

I know it looks like crap now, Got paneling temped on to keep the some of the nasties out of the house until I figure this out. The plan is to re-insulate and drywall the whole back wall.

Opinion? Idea? I have a call in to Supervent tech but haven't heard back. I'm getting antsy...

 

[cableman]

According to the instructions, with the box 1" past the cathedral ceiling the class A has to be 5" more into room. 2"=4 and 3"=3. This is on the 12/12 pitch.
Is the 2x6 frame gonna stay and the box mounted to that?

 

[DAKSY]

I'd say you're on track. As far as the attic insulation shield goes,, it has to be higher than whatever insulation is between the ceiling & the roof.
Generally, that insulation shield should then be capped with something similar to a storm collar to prevent ANYTHING from getting between
the Class A & the shield. If you have access to a bending brake, you can make your own shield & run it all the way to the underside of the roof sheathing.

 

[BamaRama]

Is the 2x6 frame gonna stay and the box mounted to that?

Yes, and a 2x4 goes on the beam to attach the sheet rock. Will also have a lift up service panel. Once i get a location for the box, I'll take it down and frame it, then put it back and tie it in to the rafters. I saw the chart but decided that since the ceiling will not be sloped where in comes into the room, it doesn't apply? The lowest listing on the chart is 1". If the beam wasn't there,that is what I would use. Maybe I'll play it safe and bring the box 1" below the beam, then it cant be disputed.

that insulation shield should then be capped with something similar to a storm collar to prevent ANYTHING from getting between the Class A & the shield.

I was thinking about blocking the whole dropped area off buy nailing to the face of the rafter and then block off the long ends of the 2x6 frame up to the roof. If it weren't for the beam, I could use a regular round ceiling support and shield.

Stupid beam!

Thanks for your thoughts.

 

[Oldman47]

You are going to need adequate spacing to that ridge beam , not just miss it. If you just box in the area above the 2x6 frame you will have created a "chase". As long as there is no insulation inside that chase you should not need a shield, at least as far as I understand it. You will still need the support structure to hold the weight of the chimney and to maintain spacing to your 2x6 frame.

 

[BamaRama]

You are going to need adequate spacing to that ridge beam , not just miss it.

Thank you for your thought. There will be the distance the support box provides plus about 6 inches (from the rafter + 1.5 to the beam) horizontal spacing from the beam. Shouldn't that be enough? My concern is with vertical. I'm not sure of the definition of "finished ceiling" so I think the most indisputable solution would be drop the box down 1" below the beam with 1" of chimney protruding into the room.

And I want to insulate the dropped ceiling so I'm going to need to use something and I want to use the Attic Insulation Shield , but I cant find anything that tells me the shield is made to fit a Cathedral Support Box. I do have some sheet metal, both stainless and galvanized that i can use to build a shield.

 

[Oldman47]

If you are installing a flat ceiling, why are you looking at a support made for a cathedral ceiling? Use the one made for a flat ceiling as it will include the insulation barrier that you need. (It is sort of a cylinder that fits around the chimney pipe with a top that blocks out any spilling over the top into that space.) The entire chimney must clear any combustibles by a full 2 inches so 1.5 inches will not be enough. The support will automatically give you that 2 inches to the box you build around it but from there up you need to maintain that clearance. That includes measurements to the ridge beam, rafters, roof sheathing and any trusses that may be involved in your install. Before you put the flashing on from the roof top, look down through the roof at the chimney. If there is anything at all within those 2 inches of the chimney, you messed up something that needs to be corrected. The roof flashing will hold that final dimension for you once it is in place.

 

[begreen]

If it's a suspended ceiling there's no structure to attach to. The cathedral support box would attach to the real ceiling between the joists above and then project through and past the suspended ceiling. Main thing here is to be sure the clearances for the connector pipe are still correct.

 

[BamaRama]

If you are installing a flat ceiling, why are you looking at a support made for a cathedral ceiling?

The clearances though the attic are not a problem. The problem lies with clearance of everything below the ceiling. If I use a round support box, I gather that the chimney pipe does not enter the room below the beam. I've never seen any of this other than the not so good pictures and descriptions on the internet but from what I have found, this is how I think this works;

Round support - the adapter attaches to the chimney, then the pipe/adapter assembly is held in place by the bottom of the support and cannot protrude any further down.

Cathedral support - the chimney slides though the bottom of the box and held in place by a clamp, then the adapter attaches to the pipe.

And I'm close on my double wall 6" clearance from the finished wall. The round support takes me 3/8 closer to the finished wall with the stove pipe.

 

[BamaRama]

If it's a suspended ceiling there's no structure to attach to.

I'm not sure what you would call the ceiling I'm using, but without it, the pipe would have to go out the back wall or use a 36" cathedral box, and I'm not sure that would be long enough to clear the beams. Using this approach I can have service access to the space between the ceiling and roof. I ran a ceiling fan wire up there not long ago and it was almost impossible.

 

[webby3650]

If you are installing a flat ceiling, why are you looking at a support made for a cathedral ceiling? Use the one made for a flat ceiling as it will include the insulation barrier that you need. (It is sort of a cylinder that fits around the chimney pipe with a top that blocks out any spilling over the top into that space.) The entire chimney must clear any combustibles by a full 2 inches so 1.5 inches will not be enough. The support will automatically give you that 2 inches to the box you build around it but from there up you need to maintain that clearance. That includes measurements to the ridge beam, rafters, roof sheathing and any trusses that may be involved in your install. Before you put the flashing on from the roof top, look down through the roof at the chimney. If there is anything at all within those 2 inches of the chimney, you messed up something that needs to be corrected. The roof flashing will hold that final dimension for you once it is in place.

The cathedral ceiling support will work just fine on a flat ceiling. The round flat ceiling support does not come with any kind of insulation shield, it's only 4" tall, whereas the cathedral support is 18" tall.

 

[webby3650]

The clearances though the attic are not a problem. The problem lies with clearance of everything below the ceiling. If I use a round support box, I gather that the chimney pipe does not enter the room below the beam. I've never seen any of this other than the not so good pictures and descriptions on the internet but from what I have found, this is how I think this works;

Round support - the adapter attaches to the chimney, then the pipe/adapter assembly is held in place by the bottom of the support and cannot protrude any further down.

Cathedral support - the chimney slides though the bottom of the box and held in place by a clamp, then the adapter attaches to the pipe.

And I'm close on my double wall 6" clearance from the finished wall. The round support takes me 3/8 closer to the finished wall with the stove pipe.

You are absolutely correct, the cathedral support allows the pipe to protrude into the room as far as you need it to. The round flat ceiling support does not allow any chimney to protrude into the room. So if there are any obstacles, the cathedral support is the way to go. That's what we use primarily because it always works. The round support only works on a hand full of jobs.

 

[BamaRama]

Thanks Webby. I'm slowly figuring this out. I just made the connection as to why they sell black chimney pipe.

Is there a required horizontal distance from the beam other than to facilitate the stove pipe clearance? I'm thinking the beams declining elevation may come into the picture.

 

[webby3650]

Rub the pipe down with some vinegar, then paint it black. We do it all the time.

 

[BamaRama]

Is DSP okay 6.5 inches away from standard light weight gypsum board wall? This will only be a 2' pipe run from the ceiling before 45ing away.

All of the gypsum board I can find says in the submittals that gypsum board is not recommended where it will be exposed to temperatures exceeding 125°F (52°C) for extended periods of time. Then the product description says an advantage is that the gypsum core will not support combustion or transmit temperatures greatly in excess of 212°F (100°C) until completely calcined, a slow process.

This sheet rock is going on the wall in a living area behind an NC-30 which requires 13" clearance. Then the smoke pipe goes up to the chimney connector that is as described above.

I looked at the X coded stuff and it gives the same 125* recommendation.

 

[webby3650]

The minimum is 6". Stick to that and you'll be fine.

 

[BamaRama]

Thanks Webby, I just realized i may need to put a smoke pipe tee at the chimney connector for a clean out since i have a 12/12 roof that is 25" off the ground. Does this make sense?

 

[webby3650]

That depends on the stove really. If it has a removable baffle then I wouldn't use a tee. If the set-up allows for it it sure wouldn't hurt.

 

[bag of hammers]

I've done 3 installs in the last few years and used cathedral box on all 3. One was a flat ceiling but the box was available and it works well even on a flat ceiling. In my LR the supervent drops several inches into the room through the bottom of the box - mostly for connector / pipe clearance (steep pitch). Painting it is kinda on the radar as Webby suggests but haven't got to it yet and in any case the stainless isn't so bad to look at IMHO. Good luck...

 

[BamaRama]

I've done 3 installs in the last few years and used cathedral box on all 3.

That's good to know. I felt like I had three heads or something. In the configuration I'm using, that's all I can figure will work. My only concern was with an insulation shield since it goes through a 50+" attic with insulation on the ceiling above the box. I called Supervent tech support. He said to use sheet metal to extend the box up to butt to the underside of the roof... and an attic insulation shield will not work with a cathedral box. Never seeing any of this stuff before propagates stupid questions.

If it has a removable baffle then I wouldn't use a tee.

I plan to buy an NC-30. The literature says it has a baffle. Haven t seen the stove so I'm not sure. It's an offset setup so a tee would work but, from what I gather, the 90* turn will slow the draft more than two 45s.

 

[begreen]

You've been asking great questions. Nothing stupid about them.

 

[webby3650]

The attic insulation shield will work with a cathedral ceiling support. The person on the phone misinformed you.

 

[DougA]

He said to use sheet metal to extend the box up to butt to the underside of the roof... and an attic insulation shield will not work with a cathedral box.

If you need to extend it, you can buy sheet metal used for duct work at HD or any good hardware store - cheap.
Webby is right, not sure you understood the answer on the last part or they misunderstood your question.

 

[BamaRama]

Webby is right, not sure you understood the answer on the last part or they misunderstood your question.

I believe you guys when you say it will work, but the guy emphatically stated the the attic insulation shield is not designed to fit a cathedral box. I couldn't find any good info that says it is designed to fit, so that's why I called. Sent him pics of the attic. Maybe they haven't tested it in this configuration?

I have enough scrap .024, stainless and galvanized, that I pulled off of the old zero clearance unit to build the extension and the tools to do it with. A 12" square box can't be that difficult but a store bought shield would be easier.

 

[webby3650]

Well they never tested their ceiling box with a homemade extension either.
The bottom of the insulation shield is a perfect fit on the ceiling box.