Floor protection question

[Jason1]

Hi. I'm new to this forum, I have spent a couple hours reading the very helpful information at Hearth.com, but I can't find an answer to my question. I have an older Haugh's wood stove with a Warnock Hersey tag on the back (1983). I'm about to build a new hearth, and although most of the clearance measurements are very clear, it is the floor protection statement that I'm not sure how to interpret. It reads "protect floor with 3/4" asbestos pad or equivalent". I obviously can't get an asbestos pad anymore, so what would be an equivalent? I'm building a raised platform with ceramic tile or slate, so would 1/2" cement board under the tile suffice?
Thanks for any helpful suggestions.

 

[elkimmeg]

I can look up the generic NFPA code and advise using that, but I have to know leg height.

we can advise here, but you local inspector has final say on these matters. If I supply you the NFPA requirement it might make it
easier to obtain a permit.

Welcome to the hearth

 

[thechimneysweep]

According to the chart at http://hes.lbl.gov/hes/makingithappen/no_regrets/insulationold.html, asbestos has an R value of 1.0 per inch, so you'll need a material with an R value of 0.75. There's a chart showing the R value of several commonly used hearth materials on our website at (broken link removed to http://www.chimneysweeponline.com/horvalue.htm).

 

[webbie]

Another link:
https://www.hearth.com/econtent/index.php/articles/k_values_what_does_it_all_mean
and another:
https://www.hearth.com/econtent/index.php/wiki/Hearth_Design/
(see chart down the page....

My suggestion - use 4 layers of 1/2" durock or wonderboard - it's fairly cheap and you can use thinset to adhere tile to it.....

 

[njtomatoguy]

maybe this helps

 

[webbie]

NJ, that hearth is not equiv. to 3/4 asbestos - it is pretty much a minimum "spark" type hearth for use with a stove higher on a pedastal.

To get to the R-value of asbestos (and who know why they used that is a manual LONG after you could not get it any more), the person would have to use either 4 layers of cement board (1/2) or perhaps a think layer of Micore, then one layer of cement board and then tile.

Lots of ways to skin the cat - many times a matter of exactly what a person wants it to look like.

 

[Jason1]

WOW, you folks are great-and FAST. So, it looks like I need more protection than I thought. The stove is actually going on a cement slab foor, but since there is 5/8" plywood on horizontal 1/3s below the carpet for the rest of the floor I figured I would get above the carpet level using 2X6 framing. I'll have to check out the hardware store for this Micore stuff, but it looks like I might have to avoid combustable materials and stack wonderboard until I get the height I want ( I hope this wonderboard is cheap).
OK Elkimmeg, I would be interested to know what the NFPA code says for when the fire chief asks what I have under that beautiful tile. The legs are 7", there is also a suspended piece of sheet metal (not sure the guage, but looks like 1/16") 1 1/2" below the bottom of the firebox. There is also 1 1/4" firebrick lining the bottom of the firebox.

 

[nshif]

If you use metal studs you can maintain CTC without stacking too much cement board

 

[webbie]

Given those legs and heat shield, you are unlikely to have much downward radiation. Just about any decent protection will do. If the unit sits on a slab, NONE is needed, so you can forget earlier advice. Sounds like your floor is a total of 1 1/2 inches thick. Use three layers of Durock or Wonderboard (pretty cheap stuff) and then tile (use thinset mortar). That way you have no framing underneath to protect.

The NFPA code is "generic" and does not really apply to your stove - because you have instructions. But if you did not, that leg length would make the heath able to be less than we have specified. Another option is to cement 2" or 4" solid blocks or bricks down to the slab- again, no R value required unless frame is under the stove area.

 

[nshif]

Web
He said he was going to raise it with 2x6 framing which means the slab is meaningless unless he uses metal studs.

 

[Jason1]

I went to Home Depot at lunch and found that 1/2" 3X5 wonderboard is $20/sheet. That's not cheap in my book! (4X8 drywall is $11)
I also looked at new stoves. The tags on the backs are similar to mine, I really looked at a non EPA model. It looks the same as mine except the doors and the air vents, the legs are the same length and the suspended heat shield is exactly the same. For floor protection it reads: "3/4" millboard pad", again this made me sweat a bit because I'm not sure what that is-though at least it didn't have asbestos. Anyway, I opened it up and found the installation manual. Fortunately it clearifies that grouted ceramic tile is also good floor protection. Therefore, my reasoning says that I only need my tile on top of any plywood if I do build it up. I think I would be extra safe putting 1 layer of wonderboard below the tile just so I can sleep at nigh. Am I crazy?

 

[thechimneysweep]

Hi Jason,

Warnock Hersey is a UL-accredited test lab; they tested your stove and found it needed R-0.75 (3/4" asbestos) floor protection. The fact that another stove went through testing and was found to need R-0.020 (1/4" ceramic tile) floor protection doesn't mean you can reduce the R of your hearth, no matter how similar the two stoves look. This is the very reason stoves undergo testing: so you can be given the exact floor protection requirements for your exact stove. I urge you to bite the bullet and provide the floor protection the test lab specified.

 

[jtp10181]

Ceramic tile has a near negligible R value. For most fireplace you would need like 20 layers of tile to meet the minimum requirements (if only using tile). Just having tile over plywood would be a bad idea IMO.

 

[stoveguy2esw]

Hi Jason,

Warnock Hersey is a UL-accredited test lab; they tested your stove and found it needed R-0.75 (3/4" asbestos) floor protection. The fact that another stove went through testing and was found to need R-0.020 (1/4" ceramic tile) floor protection doesn't mean you can reduce the R of your hearth, no matter how similar the two stoves look. This is the very reason stoves undergo testing: so you can be given the exact floor protection requirements for your exact stove. I urge you to bite the bullet and provide the floor protection the test lab specified.

best advice you can get right up there ^ remember also that these guys are pro's Tom is exactly correct, different stoves have different requirements , even ones that look very similar. older units tended to run hotter in testing due to less restriction than is built into modern units. which focus more heat towards the tops of the unit and less below due to that restriction causing lower primary fires and hotter secondaries above, the technology between the two units you looked at even though it was an exempt unit are different. i have to join Tom and urge you to follow the guidelines provided with the listed requirements for the stove you are installing, because sleeping at night is a wonderful thing, and waking in the morning is even better.

 

[Gooserider]

Agreed. You should build your hearth to AT LEAST the standards mentioned on the label / stove manual. More won't hurt, less could be a problem. Also hearth designs are based on the idea that the stove is sitting on a surface that is at least level with, or higher than, the surrounding floor. If I understood your description, I believe you have a floor that is elevated above the slab, your hearth needs to be at or above that height. From your description it sounds like you need about 1.5" of thickness to get that, and I think the easiest / cheapest way to do so would be to just stack three layers of 1/2" Durock on the slab and cover them with tile.

BTW, it appears that HD does not carry Durock any longer, but Lowes has it for $9.85 / sheet (3'x5') here in MA. Durock is IMHO the best stuff for this, though Wonderboard is almost as good. DO NOT use "PermaBase" as it is made with styrofoam beads in the cement that make it a combustible material.

There is an article on hearth construction in the Wiki that goes into more details.

Gooserider

 

[elkimmeg]

Web and nshif gave similar advice If you can go down to the concrete slab you can build it up using non combustibles and do not need to worry about r-value remove the rug and plywood below build up you slab with either concrete blocks or metal studs and top it off with cement board then tile it Keep it simple as possible there are metal 2/6 studs you can use.
no special cutting tools needed just tin snipe will work and sheet metal screws

 

[Jason1]

Ok, thanks! This is why I asked. I have read a couple threads with people building a hearth using steel studs and topping with Durock. This is what I am doing to the back wall (cinderblock, but again I need it flush with the rest of the wall). Those steel studs seem so flexible, I just can't see how they could hold up all that weight! Are they made thinner here? Since I only need to raise the slab 1 1/2" -2", I've thought of just pouring a 2" slab of mixed concete, then tile.
I'm glad I checked out newer stoves because they need a clearance of 56" from the top of the stove to the ceiling, and since my total clearance is only 7ft, the 2X6 raised platform is now out anyway. I want to make sure this hearth will still be okay if I get an EPA stove down the road.

 

[Gooserider]

Ok, thanks! This is why I asked. I have read a couple threads with people building a hearth using steel studs and topping with Durock. This is what I am doing to the back wall (cinderblock, but again I need it flush with the rest of the wall). Those steel studs seem so flexible, I just can't see how they could hold up all that weight! Are they made thinner here? Since I only need to raise the slab 1 1/2" -2", I've thought of just pouring a 2" slab of mixed concete, then tile.
I'm glad I checked out newer stoves because they need a clearance of 56" from the top of the stove to the ceiling, and since my total clearance is only 7ft, the 2X6 raised platform is now out anyway. I want to make sure this hearth will still be okay if I get an EPA stove down the road.

A poured slab would definitely meet all requirements for any stove you would put on it, as long as it's dimensions (L x W) were adequate. Same with stacking Durock - at $10/sheet for 3x5 sheets, you'd only need $40-50 worth to build a 2" thick hearth, which might be cheaper / less hassle than mixing concrete - but it doesn't matter that much which way you went as the results would be the same.

On the ceiling, the clearance isn't a big issue as you can get a considerable reduction in the 56" normal requirement by using the same sort of ceiling protection as you will frequently see mentioned for walls - Non-combustible material spaced 1" down from the ceiling with non-combustible spacers, open around the sides. You'd have to check to see just how much reduction that allows you, but I think it will let you fit just about any EPA stove into the space.

Gooserider

 

[elkimmeg]

Goose Ceiling reductions using the one inch spaced Wonder board /ect is only a 33% reduction. In this case would add the difference of raising the hearth

I like the idea of pouring the hearth only two 60 lbs bags needed less than $8

 

[Gooserider]

Goose Ceiling reductions using the one inch spaced Wonder board /ect is only a 33% reduction. In this case would add the difference of raising the hearth

I like the idea of pouring the hearth only two 60 lbs bags needed less than $8

Well I think the 33% reduction is pretty significant, gives about an 18" reduction - takes a 56" requirement down to about 39" or so... Call it 40" to be conservative, the OP said he had 7' or 84" to work with - a tall stove is going to be around 36" - so that would imply he could use up to about an 8" pedastal before having clearance issues. Going with the 2" pedastal, he could have a 42" tall stove with the protector, but only a 26" tall stove without it - a tight squeeze...

As to the hearth, nothing wrong with the poured slab approach - each method has it's own hassles in construction, I would say it's a question of which the OP preferred to work with, as they are interchangeable from a safety / code standpoint.

Gooserider