OT: Fireplace insulation?

Not a tool, but I know many of you may have experience here, so I hope you can follow my question. I have a new shed-roof addition on the back of my house. I am installing a pre-fab (zero-clearance) fireplace diagonally across one corner. (Imagine a triangle with the fireplace on the bottom leg of the triangle.) I understand the need for various clearances, correct pipe, etc., so no issue there. My question regards insulation. I will insulate the outside walls of the corner. But should I insulate the diagonal wall that encloses the fireplace (the bottom leg of the triangle)? Some sources say no insulation on that interior wall so the fireplace chimney will be closer to room temperature and reduce condensation in and on the pipe. Other sources say insulate the enclosing wall to keep the chimney pipe cold. Which way should I go? (Does this question make any sense? if not, I can re-explain.) Thanks.
 

Can't answer the whole question but a warm chimney build less gunk than a cold chimney and it will draw better.
 
I have exactly that set-up in one of my houses---corner pre-fab, raised 15" off the (wood) floor. No insulation, no problem. But, I live in Louisiana, not Minnesota. I like that fireplace better than the masonry one in my other house.
 
I am blessed to live in an area where I don't have to answer to building codes or inspections other than electrical. That said, I always build to at least code in the city a mile away (in case my area ever gets annexed), but its code doesn't address my inside-wall insulation question. Manufacturer's specs don't address my insulation question other than distances from flammable materials, which I'm following.
 
Seems I understand your description, you are referring to the bottom triangle leg of the wall above the front of the fire place, and whether to insulate that or not?

I would first refer to the manufacturers product data, drawings, details or at least send them a request for information, that and verify what the building code may require. I would want to know what the details are for a typical installation if at all possible.

In my opinion, and if I understand what you are building correctly, then there is a fire box which I assume has refractory brick or is built in a manner that its insulated so that the exterior of it cannot get hot, as it is enclosed by a combustible wall. Same with the flue pipe, being triple wall or what have you. If that is the case, then there should be no heat issues in this annular space that is created by the wall which encloses it.

I would suggest a material such as Roxul Mineral Wool, given its properties and the UL fire rated assemblies its commonly used for, in addition all the UL testing its been through, it may be what you need here. This material is mainly used in UL rated fire resistance assemblies, for instance pipe penetrations through concrete floors, compressed 50% and covered on each side with fire stop material. It fills the annular space around the pipe and then continues the same rating of the floor to where it terminates against the pipe. Its also used for sound attenuation. See the below link.
Roxul Mineral Wool
 
I commonly see that wall insulated in the NW Iowa/South Dakota area. Not saying it's right but that is the common way with a general contractor that builds 50+ houses a year and others who build fewer homes. That being said it sounds to me like maybe it should not be insulated. As an after thought most of them are gas fireplaces here.
 
Billy NY said,"Seems I understand your description, you are referring to the bottom triangle leg of the wall above the front of the fire place, and whether to insulate that or not?
I would first refer to the manufacturers product data, drawings, details or at least send them a request for information, that and verify what the building code may require. I would want to know what the details are for a typical installation if at all possible.

In my opinion, and if I understand what you are building correctly, then there is a fire box which I assume has refractory brick or is built in a manner that its insulated so that the exterior of it cannot get hot, as it is enclosed by a combustible wall. Same with the flue pipe, being triple wall or what have you. If that is the case, then there should be no heat issues in this annular space that is created by the wall which encloses it."

Yes, you've interpreted my description correctly. No building code involved, and I'm meeting or exceeding manufacturer clearances. I'm kind of wondering, along with concerns in my original post, if I leave the wall above the firebox uninsulated will cold air sitting in the chimney make that part of the room feel chilly? It's not a huge section of wall, so maybe a moot point. Thanks for your advice.
 
It seems to me that you would want it not insulated; I don't see how adding insulation there could keep the chimney cooler. Uninsulated it would dissipate more heat into the room.
 
Years ago I did something similar in a mountain cabin. Walls in the corner were 5/8" Sheetrock over Fiberglass batts. I installed shiny (read reflective) corrugated sheet-metal in the corner, 2" off the floor and 2" away from the walls using ceramic stand-offs. Then I installed a wood-burning cook-stove/fireplace (tempered glass fire-door so you could watch the flames) & a fan-forced "Stack Robber" on the stove pipe. (For BAKING, I use a portable sheet-metal Oven on top of the stove). Stove pipe went up through a Triple Wall Cold Collar in the roof, 2 foot section of stove pipe above the top of the Cold Collar & a Rain Cap on the top of the stove pipe. It works GREAT, NO PROBLEMS!

Doc
 

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