Someone tell me if I'm crazy or not:
The manual for my north star says the Hearth Extension must have a min. thickness of 1" and k-value of 0.49. Or, use "alternative materials calculation" for R-Value., which it does not give, but gives a method (standard formula) for solving for R from K and a thickness.
Since I'm using multiple materials (no one wants micore as their only material, not to robust of a surface material for a hearth)...anyhow..
So if I convert thier K to R, that's R=Thickness/K right?
That's R=1"/0.49 = 2.04.
SO I need R of 2.04 to meet spec.
I'm building a 6" raised hearth extension, with a piece of 1.5" of slate for the top surface. So I have 4.5" below the slate to the OSB floor.
By my sources, the 1.5" of slate is 0.15 R, so I'm down to 1.89 R needed now. Durarock is 0.26 R for every 1/2" . 1.89/0.26=7.27 or 8 layers of 1/2" durarock, that's 4".
My first though is, WTF? 4" of durarock? Whatever...
THen I flip the page and still in the "alternate materials calculation section" it has a table which is entitled
"Hearth Extension Insulation Alternatives - Min. R-value of 2.18 required"
2.18? Where'd that come from...ok..whatever, my 8 layers of durarock plus 0.15 of slate is still good. But then IN the table, it lists Durarock at 0.52/Inch of thickness, ok, that's right, then there's a column for "Thickness required" and it says 2.25" for the durarock?
Where's the 2.25" come from? 2.18/0.52=4.19 inches, not 2.25. Am I crazy or is something wrong with what they printed or did I miss something here.
At any rate, 2" or 4" , plus the 1.5" of slate, I think that's way overkill if you ask me. The old ZC open fireplace had a piece of 1/2" marble glued to plywood on top of a 2x4 platform. The flashpoint of a block of average wood is about 300C, I thinkk with 2" of durarock and 1.5" of slate I could build a fire on the hearth extension and not worry about the OSB underneath catching on fire.
The online manual is even more stringent, it seems the version posted at HeatnGlo's website for the North Star is an older version than the one that came with my North Star. It doesn't have the table of materials in it, and it lists the K value required at 1.5" min. thickness at 0.43K. WTF? 1.5/0.43=3.48R. 3.48??????? Let's see...for durarock, 3.48/0.26 13.4 layers of durarock or 6.7" worth. There's only 6" from the bottom of the fireplace fasica to the floor, so one would HAVE to have raised the fireplace up at least 3/4" of an inch off the floor to be in spec. Either that or use Micore which is very difficult of find unless you want to order a pallet of it.
I think 4 layers of durarock plus the slate, on top of some framed platform is plenty.
My other idea is to just use metal framing studs with 1 layers of durarock on top and 1 layer on the bottom, plus the slate on that, because dead air space is 0.97R/inch and I'd have 3.5" worth.
The manual for my north star says the Hearth Extension must have a min. thickness of 1" and k-value of 0.49. Or, use "alternative materials calculation" for R-Value., which it does not give, but gives a method (standard formula) for solving for R from K and a thickness.
Since I'm using multiple materials (no one wants micore as their only material, not to robust of a surface material for a hearth)...anyhow..
So if I convert thier K to R, that's R=Thickness/K right?
That's R=1"/0.49 = 2.04.
SO I need R of 2.04 to meet spec.
I'm building a 6" raised hearth extension, with a piece of 1.5" of slate for the top surface. So I have 4.5" below the slate to the OSB floor.
By my sources, the 1.5" of slate is 0.15 R, so I'm down to 1.89 R needed now. Durarock is 0.26 R for every 1/2" . 1.89/0.26=7.27 or 8 layers of 1/2" durarock, that's 4".
My first though is, WTF? 4" of durarock? Whatever...
THen I flip the page and still in the "alternate materials calculation section" it has a table which is entitled
"Hearth Extension Insulation Alternatives - Min. R-value of 2.18 required"
2.18? Where'd that come from...ok..whatever, my 8 layers of durarock plus 0.15 of slate is still good. But then IN the table, it lists Durarock at 0.52/Inch of thickness, ok, that's right, then there's a column for "Thickness required" and it says 2.25" for the durarock?
Where's the 2.25" come from? 2.18/0.52=4.19 inches, not 2.25. Am I crazy or is something wrong with what they printed or did I miss something here.
At any rate, 2" or 4" , plus the 1.5" of slate, I think that's way overkill if you ask me. The old ZC open fireplace had a piece of 1/2" marble glued to plywood on top of a 2x4 platform. The flashpoint of a block of average wood is about 300C, I thinkk with 2" of durarock and 1.5" of slate I could build a fire on the hearth extension and not worry about the OSB underneath catching on fire.
The online manual is even more stringent, it seems the version posted at HeatnGlo's website for the North Star is an older version than the one that came with my North Star. It doesn't have the table of materials in it, and it lists the K value required at 1.5" min. thickness at 0.43K. WTF? 1.5/0.43=3.48R. 3.48??????? Let's see...for durarock, 3.48/0.26 13.4 layers of durarock or 6.7" worth. There's only 6" from the bottom of the fireplace fasica to the floor, so one would HAVE to have raised the fireplace up at least 3/4" of an inch off the floor to be in spec. Either that or use Micore which is very difficult of find unless you want to order a pallet of it.
I think 4 layers of durarock plus the slate, on top of some framed platform is plenty.
My other idea is to just use metal framing studs with 1 layers of durarock on top and 1 layer on the bottom, plus the slate on that, because dead air space is 0.97R/inch and I'd have 3.5" worth.
