R2 hearth required for Englander 13NC

[JPapiPE]

I have decided to build my own hearth and it seems the cheapest way is the durock and steel stud method. I'm guessing that it would take 2 layers of 1/2" Durock and 2 or 3 steel studs. Perhaps a single layer of durock would do with the studs but I afraid my Englander 13NCH would crash through such thin protection. I have also considered micore as hearth material, but I can't seem to find it anywhere around here. Perhaps it could be special ordered. Any help would be appreciated. I know durock sells for about $11 for a 3x5' sheet at the closest HomeDepot, but they don't carry micore.

 

[webbie]

What R=Value do you need?

Most stoves need somewhere about R=1, and that could be done this way.....

cut carpet
make wood frame around outside of hearth pad - which would be as thick as pad - but not fall within the clearances...
lay one sheet of sheet metal on the floor - screw or nail down
lay 5 or so Hat channels (lowest profile) or use steel studs - screw through to floor to stabilize
place 3 layers of cement board on top, using a small amount of glue between and screwing all down to the studs
lay tile on top, and grout right up to the wood you used for the frame.

Such a hearth would probably be R=1.2 to R=1.5+
If you needed more, just use cement board on the floor - one sheet and then 3 or 4 on top of the hat.

Actually, the studs are quite wide and probably have a much higher R value....

 

[JPapiPE]

My englander 13NC requires a 48X48" hearth with a R value of 2

Whats a hat channel?

 

[webbie]

shaped like this.

Used for drywall - available at drywall supply houses.

 

[thechimneysweep]

 

[JPapiPE]

I might as well start a new thread because I can't understand all the information i'm receiving on how to build a safe hearth. I'm not exactly dumb but just maybe a slow one to understand a new science. I do hold a Masters Degree in Structural Engineering and am registered with the state of Maine as a P.E. (professional engineer) . I guess I'm obtuse in some ways, but I do know steel, concrete and glass, sealants, load and flex in my sleep. Plus I know the little secret that manufactures hold secret : like a 10% error factor or more is built into calculations. .I deal mostly in 3 forces: Compression. Tension and Sheer values plus a little more. I build bridges and tall buildings. Have for over 30 years.

None of my structures have falled to date...just lucky i guess. Oh and I should say i'm retired or disabled is a more accurate description of my woes. ( hit in the back with a steel beam and a recent heart attack)

I seem to be getting a view from this forum that a product called micore is a very efficient heat barrier. Much more so than bricks and durock. OK, then I can call in some favors and get micore from some wholesalers I used to deal with. They like me ...I make people feel good about their situation by explaining how bad it could actually be.

So my question Is: How much micore (stacked vertically) do i need to attain an R-2 level in my woodstove hearth? Very simple.

 

[webbie]

https://www.hearth.com/econtent/index.php/articles/k_values_what_does_it_all_mean

2.33 per one inch of Micore......but, once again, in terms of compression it cannot take a stove leg on it. That is why a composite construction is required! Consider it like a wall or floor assembly - the FG insulation provides the R-Value but you cannot hang pictures on it or paint it. SAME HERE. R-Values are higher based on lighter density of a material (more air trapped inside).

http://www.mcmaster.com/

has lots of insulated hi-temp boards - but local drywall supply houses also usually carry something like it.

 

[begreen]

Sometimes I think that being an engineer must be a curse. I haven't heard of people with cracked hearths due to flexing when they are built well. Did you contact the owners of any of the hearth building articles previously posted? There will be no flexing with metal studs placed 12" OC, with 2 layers of durock on top if the durock is screwed down per manufacturer's recommendation. If you're still concerned, put a skin of sheetmetal on top of the studs and pop-rivet it down as a lid before the durock is screwed down. That baby is not going to flex.

Do a search on the many posts here by folks that have built their own hearths using metal studs.
https://www.hearth.com/econtent/index.php/forums/viewthread/11825/P30/
https://www.hearth.com/econtent/index.php/forums/viewthread/13600/
https://www.hearth.com/econtent/index.php/forums/viewthread/8289/

However, a hearth can also be built by sandwiching micore with a durock top. Micore is R2.33 per inch. Durock is about R .52 per inch. A 1/2" of micore plus 2 layers of durock then tile should do it.

https://www.hearth.com/econtent/index.php/articles/k_values_what_does_it_all_mean

 

[Highbeam]

Don't let being an engineer cause you so many problems. I am actually a licensed civil PE too, but I built my own hearth.

Two 1/2" layer of micore, Two half inch layers of durock, set a stove on top and you're done. Want an elevated hearth? or can't find micore? Then just stack 4 inches worth of straight durock. It will be heavy of course. Use the chart for the R values of various materials and make your composite. Know that some materials are heavy (durock is 96 lbs per 1/2" sheet as i recall) and that some can only handle small point loads without material failure like micore which needs a stronger material to distribute the loads.

Lastly,

"OK, then I can call in some favors and get micore from some wholesalers I used to deal with. They like me ...I make people feel good about their situation by explaining how bad it could actually be."

You don't need to do that here. We will be glad to help you without hearing about how bad it could be. I would venture to say that we don't really want to hear about it.

 

[JPapiPE]

Yes Woody i did contact another Mainer that has the same stove as mine and he said to use 2 layers of 1/2" micore and 1 layer of 1/2" durock and then tile the whole thing and then trim out the sides with Oak or another hardwood.

 

[Tfin]

Don't forget the 3/4" plywood base. You need it to secure the layers of Durock and Micore to......also its more like 1/8" or 1/4" Durock though.

 

[JPapiPE]

Yeah, Todd thats what I said ...2 layers 1/2" micore plus 1/2" durock, plus tile ...all that should equal more then the R-2 factor I require for my hearth. Maybe if the druids demnand ...I' ll add a piece of 24ga steel to put an additional protection into this mix.

 

[Tfin]

Yup, that should set you right up.

 

[blel]

Does anyone know if bluestone would contribute anything to the r value for a hearth? I am thinking of using this for the top instead on tile.Ive looked at a lot of threads but haven't seen bluestone mentioned.

 

[begreen]

I wouldn't expect much. Slate is only R .1 per inch.

 

[SlyFerret]

One of the threads that BeGreen linked to above was for my install that I did last winter.

I don't think I ever posted a link in that thread to the design that I submitted with my permit application.

http://www.crystalnetworking.net/stuff/Hearth_Pad_Design.pdf

That's the design that I used to build my hearth pad. It's not a professional CAD drawing or anything, but I thought I did a pretty good job.

-SF