Help with hearth r value question

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clark_bailey

New Member
Dec 20, 2007
22
Alabama
OK I just bought a kozy heat z42. I am confused as ever after reading the installation manual. It says to install on combustible floor but must have a non combustible layer 8 inches around and extending 16 inches out from the door. Ok, that being said I want to elevate the whole unit about 12 inches so I can have an elevated hearth extension to sit on and have my fire poker tools sitting on it. Can I place the unit on concrete blocks and build a 2x4 frame for the hearth extension and put some 1/2 inch concrete board like durock on it to satisfy the r value required. (I cannot make heads or tails from all those math formulas in the install manual) Can I build a 2x4 frame and put plywood decking on it then 1/2 inch durrock for the unit to sit on and then build the same hearth extension mentioned earlier?? I prefer to build a 2x4 frame to sit the 500 plus lb unit on and have plywood decking covered in a non combustible concrete board but-how many layers of 1/2 would be required to cover the r value needed? Also another question is how do you rock up to the edge of the unit if it say you need a 1/4 inch gap all around the front, does the 1/4 show light behind the unit or do you seal with something??? Thanks for any help, I do not want to put the unit in and feel unsafe or have to redo the install after finding out info too late.
 
OK, that fireplace unit seems to require NO non-combustible floor underneath - That means you can frame the whole base and use plywood over it and then set the unit on it. Personally, I would cover it with either one layer or Durock or sheet metal, but that is not required.

You could also use cement blocks as you mentioned.

Yes the lower hearth can also be framed, decked and then covered with enough layers of cement board to meet the spec. You should use 18" if possible instead of the 16", since the newest NFPA does call for 18" as opposed to the old 16".

If you are finishing up to the unit, there are a lot of ways to do that. A lot of folks use sheetrock until close to the unit, then switch to cement board for the last couple inches around it - seal to unit with silicone. In a lot of cases, there is wall tile of something else being installed to close off that gap also - again, you can use silicone to fasten the edge of the tile or what ever ends up being right next to the fireplace. In almost all cases, you would need either a facing material to cover that gap (tile, marble, etc.) or simply a trim or brass, or something like that.

If unit straight cement board, you would need 4 layers or 2" of Cement board.....

Hope that gets you started.
 
Put it up on 10" blocks + 2-3 layers of Durock and then finished porcelain tile. That should bring it up to about your 12" height level.

Addit: I would check the floor joists because you are adding a huge amount of weight here. It may require that you add a lally column.
 
Thank you for the replies. I am going to use 2 inch thick hearth stones for the hearth extension, so do I use 2 inches of durock with 2 inch stone on top of that? I am going to use faux rock on the sides of the unti and above the unit stuck to durock with that screen stuff that holds the fake rocks securely to the wall. As for structural sufficiency, I have 4 laminated beams (2.5 inch x 16 inch) directly under the area of the fireplace from wall to wall over a full basement area. When I built this home I planned ahead and really put way too much support under that area.
 
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