Newbie - Building a hearth

[3dogsrule]

I've been poking around and reading other posts, and I just seem to confuse myself more. I had a house built a year ago, running low on money at the time and had a crappy zero clearance fireplace put in. Not happy with it, zero heat output, hate it. Have a Hearthstone Homestead stove on layaway, and am working toward getting it installed. Okay, my current fireplace is about a foot off the ground (we wanted to leave room to build a hearth so I could sit and load wood) so I need to build a hearth high enough for the Homestead to fit into the fireplace. The Homestead manual states that for raised hearths 9" or greater that I need to have an R value of 6.6 beneath the stove. I'm hiring some weekend warrior guys to build the hearth for me. We had planned to build a support box (2x4s or whatever), put a piece of cement board on top and finish the top off with a 1.5" thick piece of granite that I had scored from my builder. But reading the chimneysweepoline.com's R value charts, that puts me WAY below the 6.6. Money and time (lack of both, long story) are big considerations, short of pouring a 12" concrete hearth, how can I come close to 6.6?? My manual is here:Homestead Manual

Help! Thanks,

Karen

 

[Corey]

The way I read it, (p9-10, diagram on p15) you need R= 6.6 on any height combustible hearth when 4 inch legs are used or R=2.5 when 6” legs are used. Or you could just make a non combustible hearth – concrete, brick, rock, etc.

Install your Hearth Mount stove with 4-inch legs on one of the following: .... A
floor protector with an R-value of 6.6 or more that you obtain from your dealer."

Install your Freestanding stove with 6” legs with the floor heat shield on one of the following:...A
composite (homemade) floor protector with an R-value of 2.5 or more.

So depending on which legs you have or want to get, that would affect the value quite substantially.

 

[3dogsrule]

I had hoped to use the 4", they're the 'hearth mount' legs and will allow the stove to set back more, whereas the 6" curve out more & force the stove out toward the front more.

 

[Corey]

It seems in that case, several layers of micor with 1/8 inch air space between would be the quickest route to R 6.6. Might double check with the company - or maybe someone else will chime in, but I suspect alternating layers of micor sheet and 1/8" thick steel washers placed in some appropriate pattern would meet the air space requirements.

 

[Wet1]

I think 6.6 might be the stiffest hearth R value requirement I've seen! What is this hearth going to be sitting on, wood or concrete? If concrete you have nothing to worry about, if wood, that's a PITA and I would have selected another stove if for no other reason.

BTW, pouring 12" of concrete would only get you R1. You'd need about 6 1/2 feet of concrete to meet the R6.6 requirement! Ideally, you'll want to use good noncombustible insulators to reach that R value w/o too much height. Cozy is right that Micore with air spaces would be an excellent choice, although I don't know how expensive or how good of a foundation that would make for a heavy hearth/stove (anyone know?). I think I would consider using hollow blocks with steel studs above and using perlite (R2.7/in) to fill all the cavities. Loose rock wool is R2.97/in and might be worth looking into as well. Cover it with Micore and cement board, then top it with your choice of tile/stone. Either way, this looks like it's overkill and a PITA.

 

[3dogsrule]

Well, the saleman wasn't spending a lot of time talking about required R values! And I wanted a stove that wouldn't stick out into the room too much and would somewhat fit back into the existing fireplace, so the Homestead was my choice from a very narrow field. Looks like a lot of my problems would be solved if I went with the 6" legs, which decreases the required R to 2.5 from 6.6. But as I said earlier, that pushes the stove out another coupla inches or so, and I was wanting there to be as small a gap as possible between the stove and the fireplace for aesthetic purposes. Ah, tough being a female, I want it functional AND pretty. Anyway, my house is post & beam, so pouring a 20 foot tall concrete hearth is out. I guess I'm digging the suggestions of using ceramic board and air gaps but will pass all suggestions along to the weekend warriors I'll be hiring (who haven't even THOUGHT about R values, which scares me). I'm totally open to any other ideas and am very grateful, thanks guys!

Karen

 

[CTburning]

From what I've read R 6.6 sounds really high. My fireview only requires a non combustible surface. I would call the dealer and seek advice from someone who knows what they are talking about. Maybe you can talk to one of the installers. Also ask about a heatshield.

 

[edthedawg]

I don't really unnerstand how the feet factor into stove placement - the whole ass end of the stove is hanging back there, way bigger than the feet.

is this some kinda partial hearthmount / surround install? or does the existing fireplace somehow manage to JUST match the width of the feet?

I would go w/ the bottom heatshield if at all possible. Page 24 shows you oughta be able to stay w/in the R 2.5 min limit under any circumstances w/ the heat shield.

And then go w/ the simple method of some steel box sections (i.e. metal studs available at a building supply co.) arranged in a supporting frame, followed by packing those empty spaces w/ 2 or 3" of mineral wool (also readily available at a building supply co.)

Make the frame fully cover and support the necessary footprint, based on rear, side, and front clearances. And double up the support in the spots you know the stove is gonna rest on.

Less the heat shield, you oughta be able to escape this one for $200ish in materials. more if you get fancy w/ tile on it.

 

[3dogsrule]

If you look at the Homestead schematics and the side view, the ass end receeds back into the fireplace. The schematics are shown with the hearth mount (4") feet. With the 6" freestanding feet, the feet curve out enough so that more of the ugly ass end of the stove would be showing, whereas the hearth mount feet would let it recess a bit more. Just trying for it to be as pretty as possible and for the pretty/soapstone part of the stove to be as close to flush with the surrounding wall as possible, so when I finished it out with a heat shield or something that it'd look good. At this point I'm about to rip my hair out and return the %$@*stove.

Karen

 

[Corey]

Ah, tough being a female, I want it functional AND pretty

LOL - yes I was thinking that R value is a little high - wondering if the stove actually had a bottom in it or the fire burns directly on the hearth. Though I don't see why you can't have form and function. The metal studs / insulation Ed mentions would work great. Or you could go ahead and build a 2x6 hearth and put plywood decking on it for strength, then arrange layers as follows:

Granite R=essentially none
micor R = 1.1
1/8 inch air space / large steel washers R = .92
micor R=1.1
1/8 inch air space / large steel washers R = .92
micor R = 1.1
1/8 inch air space / large steel washers R = .92
micor R = 1.1
Plywood

That would get you almost R=7.2 and considering: 2x6 (actually 5-1/2") + 3/4" plywood + 2-3/8" insulation stack + ~1" granite = 9-5/8 inches, so pretty close - you could mix/match dimensional lumber, sheeting, micor and/or a mortar bed under the granite to get the exact height. That hearth should then be able to survive a firey re-entry and splashdown in the ocean!

 

[edthedawg]

I haven't seen the flat washers = Micore construction method before. I used the steel studs and air gap. Knowing what I know now, I'da gone w/ Roxul (or similar mineral wool - $60 for a huge pack of it, like 10 cu ft) in between my flat metal studs. At the time, I hadn't been able to find mineral wool - just was looking for Micore and striking out, and was up against a hard time limit...

Bottom line is you need support for whatever you decide to cover it with. tile work will not greatly enjoy flexure in the substructure.

I'm also sorry to see our friend Karen here about to rip her hair out and toss aside a nice little soapstone stove...

 

[3dogsrule]

...sigh... Just talked to my stove salesman. Not only did he not know the high hearth R-value requirements for this particular stove (and he's been selling them left and right), but he'd never heard of Micore/Rescor/Fiberfrax. He was going to call Hearthstone and talk to them, and then see what he could find out about locating Micore. I called Home Depot looking for it and they hadn't ever heard of it. Fireplaces aren't a big thing here down south, but where do you northerners find this stuff?

Thanks for your support, guys, really appreciate the help, sure not getting much help locally

Karen

 

[3dogsrule]

Now wait just a minute...I'm re-re-reading the stupid manual on the Homestead, and I quote:

Install your Hearth Mount stove with 4-inch legs on ONE of the following:
A noncombustible floor, such as a slab, cement, or stone hearth. (A noncombustible floor will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or the anticipated heat from your stove.)

A floor protector with an R-value of 6.6 or more that you obtain from your dealer. (A floor protector is any noncombustible on the floor underneath and extending to the front, sides, and rear of the wood stove.)

So does that mean the hearth doesn't necessarily have to have a 6.6 R if it's just a regular non-combustible material, and what would constitute a "stone hearth"?

More confused but looking for a solution,

Karen

 

[Danno77]

well, if there is nothing combustible underneath the thing then the r-value isn't needed. that's the case with all stoves. i still can't get over the 6.6, that's wild.

 

[Corey]

The way I interpret it: If your house has a concrete slab floor on grade or something similar, there is nothing to combust, you could put the stove right on the concrete floor. If there is ANYTHING combustible under the stove...carpet, plywood decking, framing members, etc - you would need R=6.6 between the stove and that combustible material. I would interpret 'stone hearth' to mean some combination of stone/mortar/bricks/concrete which would supply the required R value.

It seems pretty silly as I don't think a 'normal' hearth would even be close to that 6.6 figure. Mine is 4 layers of bricks with 1/2" mortar at each layer which I don't think would even be 1/2 that value. But common sense would seem a fire could burn directly on top of four layers of brick and never heat up anything below. Seems like the MFR is definitely in a CYA mode!

 

[3dogsrule]

So where can the Micore be found? Stove dealer hadn't ever heard of it.

 

[edthedawg]

It's not unique for it to "never been heard'a" - happens all the time. there's other stuff, you've seen the names - all about the same stuff. But it's finicky, hard to get stuff anyways. why not just go w/ steel box studs and mineral wool and be done with it? A $60 pack of Roxul (or similar) and a half dozen $5 steel box studs from Homer's, a couple bags of $15 Versabond, 4 slabs of 1/2" Durock ($15 ea?), a buncha cheap tiles ($.77/sq ft), a $10 box o sanded grout...

whatzat - $220? ish? Mebbe you gotta spring for some buckets and trowels?

2" of Mineral Wool is over R6 by itself. The Durock and tile gets you the rest of the way.

If you want detailed layouts and section drawings of what it should look like, i'd be happy to help. PM me for the shipping address for the beer

 

[pen]

What makes me laugh is that the floor about 24 inches in front of my stove (beyond the 18 in hearth recommendation) is about 2x the temp of the floor directly underneath any part of the stove!

pen

 

[paulestuart]

3 dogs,
here is a link to micore distributors nationwide. I couldn't find any local suppliers and had to have it shipped from a state and a half away. Price was reasonable, less than 100 dollars for two sheets. they cut it up into 2'X4' segments for shipping, or ship pallets.

http://gypsumsolutions.com/distributor/BrandDistributors.asp?brand=33

Good luck - keep coming back I just found this site and it is over the top helpful.

 

[edthedawg]

Pen,

you hit the nail there modern stove w/ its big fancy glass, radiates a TON of heat right out front. just so happens the Homestead is a little funky w/ its short profile, so you got more heat right down low to the hearth.

one old suspicion is that the UL rating counted on flaming hot coals filling the ash pan, whereas normal operation usually has the ash pan empty. idk if that's true.

 

[pen]

Pen,

you hit the nail there modern stove w/ its big fancy glass, radiates a TON of heat right out front. just so happens the Homestead is a little funky w/ its short profile, so you got more heat right down low to the hearth.

one old suspicion is that the UL rating counted on flaming hot coals filling the ash pan, whereas normal operation usually has the ash pan empty. idk if that's true.

Never thought of that. Good point. I don't use the ash pan so I tend to forget about it.

pen

 

[3dogsrule]

Well, the grate inside the stove is supposed to remain closed during a fire so I wouldn't think much hot stuff should be able to get down there to the ash dump. But what do I know, the stove I had in my old house didn't have an ash dump.

I DO know that my stove dealer is selling these stoves and not recommending anything about what they set on, so there's bound to be others out there who are not meeting their R value recommendations.

I'm going to go by the dealer tonight after work and look at a couple of other stoves that my guy claims will fit into my factory made zero clearance fireplace piece of doo-doo. These other stoves don't have the same R value requirements.

I also just got through talking to the weekend-warrior guy I was going to hire to build my hearth. Sweet guy, but this is definitely not his field of expertise. Scares me, which is why I'm trying to get armed with as much knowledge as possible so I can keep him from doing things incorrectly.

Ok, now someone please answer me this: I had wanted to tile around the wood stove (cover up the parts of my crappy fireplace that are exposed after we insert the stove) and bring the tile up next to/near the stove. With all I've learned I'm a'thinkin' that's not going to be cool. My weekend warrior builder is saying we should be able to use cement board to cover up the exposed fireplace and tile on top of that. I'm thinking that I will have to buy (or have built) one of those metal surround kits and then tile outside the perimeter of that. I have no sidewalls anywhere near, FYI, from the fireplace it's 10-15 feet to the nearest side wall. So in other words, when it comes to a surround to pretty-up the install and hide my existing fireplace once the stove's in, what are my options outside of that metal surround?

My brain hurts.

Karen

 

[Corey]

Almost hard to say without seeing a picture. If I understand correctly, you're looking to extend tile off the front of the fireplace and right up to the stove? I don't think there is anything 'technically' wrong with that...durock, mortar, tile, etc will all be non combustible so they could go as close to the stove as you wish. The issue would be supporting the durock / tile - you wouldn't want it just flapping in the air and I would worry even metal studs would be a little too flexible when you start trying to hang tile.

 

[3dogsrule]

Yes, like in your fireplace picture, where the black metal surrounds the stove, I was hoping for that to be ceramic or granite tile. I think we've got enough room (depending on which stove I ultimately end up getting, now that the Hearthstone is giving me so much trouble) to attach some concrete board outside of the existing fireplace edges and tile on top of that. But with all this heat talk, and knowing that the R value of cement board is so low (and being a girl and all this stuff confusing me), I wondered about the long-term viability of the concrete board and if over the years, if the heat from being so close to the stove would either crack the tile/granite or degrade the cement board.

Karen