Cathedral Ceiling Support - Two Questions

[Skidude108]

I am building an efficient house, and installing a small wood stove in the living room.
I went to the local stove shop and they sold me a square ceiling support box with extension, and the necessary Class A pipe, but I am concerned there are a couple things they didn't think of. Everything I have is ICC EXCEL, I'll throw part numbers into my questions below.

1. The ceiling is built with trusses and is over 24" deep. They sold me the square support box ESS and extension ESSE. My roof is a 3/12 pitch so while the chimney does not exceed 5ft and doesn't need the braces, I'm afraid it isn't very well supported laterally. Should they have also sold me the Roof Support ESR? I want to avoid big braces (I don't like the look, and I'd have to go back and get them powder-coated separately) but I also don't want the chimney moving in the wind or whatever. I have installed the support box but not the chimney yet, so it's not too late to add the roof support. But I also don't want to over-constrain it if it expands and contracts with heat enough to loosen things or break.

2. There is no insulation or even air sealing in the support box, so my building envelope has a 10" x 10" area of basically R0 and the potential for air leakage at the highest/most critical location. I notice they sell an insulated version of the round support, but it seems like the only difference is the ability to air seal at the interior side and some insulation inside the support. The air barrier for my house is at the exterior sheathing, which with my square support is just a big open hole under the flashing. I don't understand how it even keeps wind-driven rain out, let alone the wind itself. Is there something I can do with this? I don't think I can just leave it as it is.

 

[begreen]

The cathedral ceiling support box plus the flashing and storm collar will provide a stable anchoring for the chimney pipe. There is no need for the ESR support. Excel sells an approved insulation (EIS) for their support boxes that can be ordered from the dealer. The amount of air leakage will be small with the unvented roof flashing once the storm collar is silicone sealed in place.

The stove will need an outside air kit (OAK) to provide combustion air in a tightly sealed home. The long stovepipe should definitely be double-walled to reduce heat loss.

 

[Skidude108]

The cathedral ceiling support box plus the flashing and storm collar will provide a stable anchoring for the chimney pipe. There is no need for the ESR support. Excel sells an approved insulation (EIS) for their support boxes that can be ordered from the dealer. The amount of air leakage will be small with the unvented roof flashing once the storm collar is silicone sealed in place.

The stove will need an outside air kit (OAK) to provide combustion air in a tightly sealed home. The long stovepipe should definitely be double-walled to reduce heat loss.

Thank you! I am absolutely going to use double-walled stove pipe.
How do the storm collar and roof flashing prevent air leakage? The installation instructions don't say anything about silicone around the top of the flashing, and it also looks like the silicone is the only thing that holds the storm collar in place. Is that right?

Edit: The stove will also use an OAK. I was planning to put a Vermont Castings Intrepid in, but I've been reading on here that VC quality isn't what I grew up with so I'm looking at other options. So far I'm just looking for what fits in the space and looks good enough to get spousal approval; I assume they can all be used with an OAK.

 

[begreen]

The storm collar and flashing fit together and that reduces the air leakage. It's not perfect, but air leakage is pretty tiny. The silicone adhesive is applied to the storm collar top where it meets the chimney pipe.