Hearth and Wall Heatshield construction

[jrcurto]

Finally I am posting after trolling for over a year, great site here guys. OK, I am constructing a corner hearth and the wall heatshields for a wood stove (undecided yet). Everything is up to local code and of course NFPA 211. As far as the 1" spacers on the wall, I am looking at several options. One would be to use strips of cement backerboard and attach them to the backside of the backerboard panels with fire proof caulk, this way I can line them up on the stud centers. Another is to purchase ceramic spacers, and finally I could use steel studs, particularly "hat channel" or steel "furring channel". I seem to lean towards using hat channel since I can fasten them to the combustible wall and drive the backerboard through them and into the studs. I have not found a source carrying 1" channel...yet. Lowes and HD only carry 1/2" steel channel. What I did consider would be steel shelving brackets, the type that mount vertically on the wall and then you use brackets to hang the shelf. I have a bunch of these from doing closets, garages, etc. I can really bolt those up nice. The question is that since these are painted, do you think they would heat enough to burn off paint or smell? Also, the hearth and shields will be finished with slate tile. With the hearth being constructed of 2X8" lumber, 12" on center joists, with bracing in-between and with one layer of 1/2" backer on top and then the tile. Is there a risk of the tile cracking or punching through the backer with a heavy stove, as in a Jotul 600? That was a long first post, thanks in advance. Jim

 

[moosetrek]

I think you'll be fine with whichever route you take for the wall spacers. Just make sure to have 1" air space, and 2 layers of Durock would be better than one. A couple comments on your floor hearth, though-
1. 1/2" Durock is not enought for a base, even over 12" on center joists. You should use at least 2 layers, set in thinset.
2. Even though the above will get you stable for the weight, you will be far from meeting some specs for stoves. As you have not yet picked a stove, that will rule out almost all that require some level of R protection for the floor (Englander, etc.), as 2 layers od Durock are only about .52 R value if I recall correctly.

 

[begreen]

Attach doubled-up 3-4" strips of cement board. You need two 1/2" strips to make the 1" spacer requirement. And screw the strips to the studs, no need for glue (or fireproof caulk?). Hat channel will work too, but there's really no need for additional material to get the job done.

 

[CarbonNeutral]

I think you'll be fine with whichever route you take for the wall spacers. Just make sure to have 1" air space, and 2 layers of Durock would be better than one. A couple comments on your floor hearth, though-
1. 1/2" Durock is not enought for a base, even over 12" on center joists. You should use at least 2 layers, set in thinset.
2. Even though the above will get you stable for the weight, you will be far from meeting some specs for stoves. As you have not yet picked a stove, that will rule out almost all that require some level of R protection for the floor (Englander, etc.), as 2 layers od Durock are only about .52 R value if I recall correctly.

You could sandwich 1/2" of micore to get another one r-unit - if you need it for whatever stove.

 

[fossil]

If you're undecided on the stove to be installed, then you might be going to a whole lot of trouble for nothing. Pick the stove, then study the manufacturer's requirements for hearth R-value and for minimum clearances to combustible materials. If there's no mention whatever in the manufacturer's documentation for the stove about allowing reduced clearances through the installation of wall shielding, then you're wasting your time and money putting them in, because you won't be able to put the stove any closer to whatever's behind the shield than you could if the shield wasn't there. Pick a stove...then design and build to it. Rick

 

[jrcurto]

Thanks guys. The Jotul F 600 requires an R-value of 0.5. I will be using two layers of 1/2" Hardibacker and that gives me R= 0.52 I dont know if the R-value of slate tile figures in but the figures look good anyway. I have to tell my wife I want the Jotul F 600 now, do you really think the open door burning with the screen in place is safe on occasion while attended? Jim

 

[CarbonNeutral]

Nice stove - I have some pictures of my f500 on slate in the perfect picture forum. The slate will give a little more r, but not much. Per the open door with screen - yes, safe as any open fire, but hold off on buying the screen - bet you won't use it. I'm glad I didn't buy it. The view is great anyway.

 

[jrcurto]

Ya, I figured the kids would be tyrying to push marshmallows through the screen anyway! I will look at your setup this morning, I see you have yours in Ivory, my wife likes it too.

 

[firefighterjake]

Thanks guys. The Jotul F 600 requires an R-value of 0.5. I will be using two layers of 1/2" Hardibacker and that gives me R= 0.52 I dont know if the R-value of slate tile figures in but the figures look good anyway. I have to tell my wife I want the Jotul F 600 now, do you really think the open door burning with the screen in place is safe on occasion while attended? Jim

Slate doesn't really give you much for the R value, but in the case of Durock (old style), two stacked 1/2 inch sheets would give you enough of a R value (I'm not sure about Hardibacker and if it's a listed material.)

Re: Open door . . . I considered getting one with my Oslo, but opted to get the rear heat shield instead. From what I've read it was a good choice . . . besides as mentioned, the view with the glass is very good . . . and with the glass in place you get a great view and heat.

 

[Highbeam]

You do realize that the hearth's R-value requirement does NOT apply to the wall which lies beyond the minimum required clearances to combustibles right? You could make that wall out of plywood if you want.

 

[jrcurto]

Thanks again. So 1/4" backerboard will be satisfactory on the wall shields? I still want tile on the shields and using lighter backerboard would be so much easier that the 1/2". I'll also check NFPA 211. Jim

 

[fossil]

NFPA's got nothing to do with it, if you're installing a modern stove with complete manufacturer's documentation. The stove manufacturer's installation instructions are what you must comply with. NFPA standards would only come into play if you were installing an old stove in the absence of such documentation, or if your stove manual specifically addresses reduced clearances through wall shielding. You keep talking about building and installing wall shields...does the manual for your stove address them? If not, then you're wasting your time, money and effort on them, because they won't buy you any sort of reduction in clearances. Rick

 

[begreen]

I'd use 1/2" cement board for the wall shield. Not really a big difference to work with, but much more rigid and stable.

 

[Highbeam]

You could use toilet paper soaked in tar as far as NFPA is concerned. You are now asking a tiling question and if I was setting tile I would want a firm and stable surface. By the time you add thinset and tile you will be 3/4" thick with the shield if using the 1/2" stuff.

Here's a thought. Why are you even using cement board? The tile walls I've torn down in bathrooms always were bonded directly to the sheetrock.

 

[jrcurto]

I hear all of ya, loud and clear. Yes it is primarily a tiling issue now since the hearth will provide adequate clearance to the combustible walls as per stove manufacturer docs. However, I am still building the wall tiling as a heat shield since that is by far the safest application. I probably would do the same if I planned on running an electric space heater on the hearth. The town building inspector and fire marshal I deal with are no pushovers either. I am overbuilding to ensure strict compliance for them as well as my home. As far as wasting time, money, and effort... I wish I could help myself there, I am an expert at all of those. The time and effort in practice will pay off as I have several people interested in the finished product which will lead to some effective bartering between them and I. I will post pics of the before and after of this project. Thanks, Jim.

 

[Wet1]

The town building inspector and fire marshal I deal with are no pushovers either. I am overbuilding to ensure strict compliance for them as well as my home.

Welcome to the forum! Better to be safe than sorry when it comes to playing with fire...

BTW, what town are you located in?

 

[begreen]

If you want thin and simple, have a piece of sheetmetal bent up as a heat shield. Paint it with high temp paint, mount it to the spacers with a 1" air gap at the bottom and it will be done.

 

[abh3]

For spacers go by the local farm supply and check out ceramic electric fence insulators, they worked great with the sheet-metal shield behind my old iron stove...