Insulating Chimney Support Box in Vaulted Ceiling

[HawkinsHollow]

So I am wrapping up an install on my wood stove. The room I will be installing it in has vaulted ceilings. So drywall, 2x10 or 12 can't remember and sheating, with
R-38 insulation. My goal is to seal up that area so hot/cold air is not infiltrating depending on the season. I will be using Duravent double wall flue to a square Duravent chimney support box at the room ceiling and then triple wall after that. How is this normally done? I have some ideas but I would like to hear what you all have done for a vaulted ceiling install. Thanks!

 

[stoveliker]

I'm not sure what exactly you want to do, but rockwool (not glassfiber) to insulate, and silicone (not flammable) for sealing.

 

[HawkinsHollow]

There will be a hole basically directly from my living space through the roof with a little bit of metal in between. I would like to seal that space as safely as possible to limit cold air in the winter and hot air in the summer from infiltrating into my living space.

I doubt people stuff a bunch of rockwool around the triple wall wall class A chimney. I am trying to find out best practices on how to do this.

 

[stoveliker]

Class A is insulated (at least double wall - not sure about triple wall...?). If you want to avoid cold air from the support box, you have to air seal by nonflammable means. Silicone is one.
The box itself will only provide a metal sheet between outside air and the inside.
Nothing flammable can go within 2" of (most) class A pipe. (Hence the attention to keep out glassfiber or cellulose insulation from the support boxes in attics with insulation shields.)
Rockwool is not flammable could in principle be put in the support box to insulate the outside temps from affecting your inside air. But I'm not 100% sure if DuraVent explicitly allows to put (nonflammable) insulation in the support box. Some brands do. But it has to be written that it's allowed.

 

[Burnin Since 1991]

Duravent specifies 2 inches to combustibles on double wall and triple wall chimney pipe. https://duravent.com/product/duraplus

Rockwool according to the Home Depot is non-combustible

Rockwool Brand on HD

The answer to your question would best be answered by the local inspectors. If you decide to use a product like Rockwool, I highly recommend that you find that info on the companies website and PDF or print it

 

[s57nomad]

I am currently working on my chimney install and stove at the moment and DuraVent for DuraTech chimney pipe states in regards to insulation in the support box it must meet certain codes and you must not compress it by more than 25% due to effectiveness on ratings.

Rockwool Comfortboard 80 does meet the criteria. See attached photos.

Also you MAY extend the support box to the roof sheathing by building an enclosed chase (DuraVent states)or extend the support box with sheet metal of similar thickness (according to my local installer, area dependent).

 

[HawkinsHollow]

I am currently working on my chimney install and stove at the moment and DuraVent for DuraTech chimney pipe states in regards to insulation in the support box it must meet certain codes and you must not compress it by more than 25% due to effectiveness on ratings.

Rockwool Comfortboard 80 does meet the criteria. See attached photos.

Also you MAY extend the support box to the roof sheathing by building an enclosed chase (DuraVent states)or extend the support box with sheet metal of similar thickness (according to my local installer, area dependent).

That is great information, thank you for that. I ended up using 2200 degree rated ceramic insulation like you would use in a forge. I lined the sides and the bottom of the support box. I then created a "seal" for the top out of a square piece with a hole cut out, like the picture shows. I air sealed the support box pretty well too. Used high temp foil tape to seal all holes and the edge where it meets the framing. I feel pretty good about it. Good luck on your install!

 

[s57nomad]

That's fantastic. Thank you!