Hearth Question

[vdog]

I am building my hearth for my Lopi Republic 1250 that will be installed on the 22nd. I have used 2x6's on edge to raise the stove up off the floor I then put 3/4 in plywood down and have 1 layer of Hardibacker cement board down and will cover that with Slate tile. My question is should I use 2 layers of the hardibacker or would that be overkill. I just thought it would be another layer if an ember got loose that it would have to get through before it got to flammable material.
Thanks
Scott

 

[Todd]

What's your stove manual say for hearth R value?

 

[vdog]

this all it says
• Floor protection must be non-combustible and at least .018" thick (26 guage).

 

[Todd]

Then I would say 2 layers would be over kill. If a couple coals happened to pop out during reload you would pick them up pretty quick anyway and even if you didn't I doubt it would hurt anything.

 

[MountainStoveGuy]

i think the two layers would be overkill, but overkill is ok. do what you makes you comfortable. Hearth pads are there for ember protection, which is easy. Embers do not have enough mass to burn through tile or hardi board. The reason some hearths have more requirements then ember protection is that the wood below will dry out and char, lowering the combustion point (pyrophoric carbonization). You dont need open flame to create combustion, just heat, fuel and good ole O2. Your case does not call for this extra protection, but it sure does not hurt to be on the safe side.

 

[firefighterjake]

I am building my hearth for my Lopi Republic 1250 that will be installed on the 22nd. I have used 2x6's on edge to raise the stove up off the floor I then put 3/4 in plywood down and have 1 layer of Hardibacker cement board down and will cover that with Slate tile. My question is should I use 2 layers of the hardibacker or would that be overkill. I just thought it would be another layer if an ember got loose that it would have to get through before it got to flammable material.
Thanks
Scott

Sounds like you basically need ember protection . . . just one layer should be fine as sparks/embers would have to get through the tile and Hardibacker board before it reached anything combustible . . . but that said, Hardibacker Board isn't that expensive and if it gives you just that extra peace of mind I might opt to throw another layer . . . plus it would give the hearth a little more rigidity to help lessen any flex that could result in popping/cracking of the tile.

 

[Wet1]

I would suggest over-engineering the hearth because you don't know what your NEXT stove requirements will be... It would really stink to rip it all up 5 or 10 years from now because your new stove has a R1+ requirement. It's not all that hard or expensive to meet those requirements now while you're building it, but it will be a major PITA later.

Just my 2 cents.

 

[MountainStoveGuy]

Now that i think about it a bit more, additional durarock really does not do much for thermal protection, if i remember correct, that stuff only has a r value of .20 per .5". If he where to change out stoves in the future, he will still be a long way from the typical requirement of r 1.0-1.5.

 

[Wet1]

Now that i think about it a bit more, additional durarock really does not do much for thermal protection, if i remember correct, that stuff only has a r value of .20 per .5". If he where to change out stoves in the future, he will still be a long way from the typical requirement of r 1.0-1.5.

That's why I said over engineer it now. Add Micore or air gap and build the R value up so any stove will work later. Make the hearth a little bigger than you think you might need too, for the same reason... plus it gives you more room to work.

 

[MountainStoveGuy]

Now that i think about it a bit more, additional durarock really does not do much for thermal protection, if i remember correct, that stuff only has a r value of .20 per .5". If he where to change out stoves in the future, he will still be a long way from the typical requirement of r 1.0-1.5.

That's why I said over engineer it now. Add Micore or air gap and build the R value up so any stove will work later. Make the hearth a little bigger than you think you might need too, for the same reason... plus it gives you more room to work.

I completly agree . But if this is not what he is going to do, one layer is no better then two. Thats where i was goin with that.

 

[John_M]

I'm with MountainStoveGuy and Wet1. Over engineer it now. Place the 2x6"s 12" on center. I would size the hearth to Canadian specifications and because it is elevated, you will want to eliminate any possibility of flex. I would suggest two layers of 3/4" plywood set perpindicular to each other. Screws holding the plywood to the 2x6"s should be placed 6" to 8" on center. I would build it to the 1.5 R value now. I believe the cement backer board should be on top because the quickset mortar sticks to it very well. Even a microscopic amount of flex will result in cracked grout. Don't ask how I know.

 

[Wet1]

I'd use steel studs (or hollow cement blocks) and a couple layers of cement board. Wood is combustible, steel studs and cement board are not, plus they will meet all code and stove requirements.