Building hearth

[kevinmoelk]

Hey fellas. Thanks for all the advice and tips.

So, yes, although probably not necessary, the more I think about it, the cost differential isn't that great to include extra material. So I've spent nearly all morning trying to find the micore and fiberfrax material, called every building supply house and every wood stove dealer. No one has this material.

I finally call a guy who specializes in fire protection. He has no retail operations, but tells me to call a company that specializes in acoutical sound deadening.

I talk to the acoustical guy who says he can get me 2x4 feet panels of this product. So my question is... is all this talk about fibrefrax and micore just acoustical panels? Can I run down to home cheapo and buy some ceiling tiles? What's the deal?



-Kevin

 

[nshif]

I agree MSG but if hes worried about upgrading in the future or someone else wanting a different stove then it may all have to be ripped out and rebuilt if the new stove calls out some outraegous r or k factor. If he wants to build for this stove Im sure his plans are fine.

 

[Corie]

Yes, Micore is something like an acoustical tile. Its often used to for cubicles in office buildings from what I've read. I don't think regular old acoustic tiles at Home Cheapo are considered non-combustible whereas obviously Micore is.

I don't mean to be the fire protection Nazi in this thread! I just don't think with the tiny price of Micore its worth skipping it. This way, you never have to think about picking those tiles up again. Just a LITTLE extra piece of mind in case you change stoves, sell the house, etc.

 

[Gooserider]

Hey fellas. Thanks for all the advice and tips.

So, yes, although probably not necessary, the more I think about it, the cost differential isn't that great to include extra material. So I've spent nearly all morning trying to find the micore and fiberfrax material, called every building supply house and every wood stove dealer. No one has this material.

I finally call a guy who specializes in fire protection. He has no retail operations, but tells me to call a company that specializes in acoutical sound deadening.

I talk to the acoustical guy who says he can get me 2x4 feet panels of this product. So my question is... is all this talk about fibrefrax and micore just acoustical panels? Can I run down to home cheapo and buy some ceiling tiles? What's the deal?

-Kevin

Standard acoustical tile is NOT Micore / Fiberfrax - Those are some kind of ceramic, probably a very distant relative of fiberglass.

The normal acoustical tile you see in say a drop ceiling is compressed CELLULOSE, aka wood or paper fiber.... I haven't tried burning it, and understand that it's treated with some kind of flame suppressant chemicals, but it's more related to cardboard and would probably be considered VERY flammable, the last thing you'd want in a hearth.

Gooserider

 

[cbrodsky]

I'll throw out an idea from Woodstock that won't help you decide R value but will give you some peace of mind no matter what you do...

Their specs for floor protection include the use of 24 gauge sheet metal in the hearth pad sandwich. The idea being that this will help dissipate hot spots and spread the load over a much larger area. The metal will conduct heat rapidly if you develop any location that is running a particularly high temperature, such as directly in front of the window on the floor, for example. Heat transfer will rapidly drive that excess heat to cooler parts of your hearth via the metal sheet and help self-correct any areas that might otherwise cause problems.

It would be a challenge to calculate exactly what this buys you for any given stove in the future, as it depends a lot on size of your hearth pad and how the stove throws off heat, but it will definitely help.

-Colin

ps - should add that the sheet metal should cover your entire hearth - not just right under the stove - goal is to transfer the heat as far as possible to relieve the load on the floor right under the stove.

 

[kevinmoelk]

Okay. Well the quest continues. Arrgh. The acoustical tile guy was bogus. He had a material that was made out of micore, but it was for acoustics, and hence had a lot of holes, voids etc. Way too soft to be putting underneath something as heavy as a wood stove, even as an intermediate layer.

No one in the Yakima valley carries either Mircore or Fibrefax. I could order an entire pallet of the stuff, but that would really be cost prohibitive, and what the heck would I do with a whole pallet?

Earlier today I had sent an e-mail to Country Stoves to ask if they had a specific value for the 3/8" noncombustible material. Country sent back an e-mail stating that the K value of the hearth must be a minimum of .86

Wow, I'm glad I asked. So now with that tid bit of information I'm a little confused as to how to calculate the K-value. The K-value for wonderboard is 1.92 per inch according to the chart someone posted earlier. So then 1/2 inch of wonderboard would have a K-value of 3.84 and an R-value of .26. Hence, if I am calculating this correctly, I would need 5 layers of 1/2 wonderboard to bring the K-value to .769 and an R-value of 1.04.

Someone please check my math, because I'm horrible. That would mean 2 1/2 of wonderboard. Egads. Maybe I'll take it off and pour a concrete slab. I wonder how thick that would have to be?

Thanks everyone for all their help thus far. I'm a little frustrated at not being further along, but I'd rather re-do some work now then later. It's only a bunch of screws at this point.

-Kevin

 

[babalu87]

Earlier today I had sent an e-mail to Country Stoves to ask if they had a specific value for the 3/8" noncombustible material. Country sent back an e-mail stating that the K value of the hearth must be a minimum of .86

Wow, I'm glad I asked. So now with that tid bit of information I'm a little confused as to how to calculate the K-value. The K-value for wonderboard is 1.92 per inch according to the chart someone posted earlier. So then 1/2 inch of wonderboard would have a K-value of 3.84 and an R-value of .26. Hence, if I am calculating this correctly, I would need 5 layers of 1/2 wonderboard to bring the K-value to .769 and an R-value of 1.04.

K value for 1/2" of MICORE 300 is .22
K value for 1/2" of CEMENTBOARD is .86
COMBINED they have a K-value of 1.08

R value for 1/2" of MICORE 300 is 1.16
R value for 1/2" of CEMENTBOARD is .26
COMBINED they have a K-value of 1.42

Using both material gets the best from both of them

What does your stove require for the R AND K values?
They should give a number for both

 

[kevinmoelk]

Country Stoves did not provide both an R and K value, only the K value.

But I thought the lower the K-value the better. Ins't there an inverse relationship at work here? I mean to say, you can't simply add up K-values like you can R-values. Or did I read that whole R vs. K values article incorrectly? Again, I'm horrible at math.

-Kevin

 

[babalu87]

Read both of these paragraphs carefully.

R-Value: The higher the R-Value,the better the insulating properties of the subject materials. R-Values are most often used to express the thermal resisitance (ability to stop heat flow) of a building wall, ceiling or floor. Because of this, most R-Values are calculated at normal temperatures of approx. 75 F. R-Values are easy to add together so calcuating the total R-Value of a wall is simply done by adding the values for the sheetrock, insulation, sheathing and siding.

K-value is a measure of heat conductivity of a particular material. Specifically, it is the measure of the amount of heat, in BTUs per hour, that will be transmitted through one square foot of material that is one inch thick to cause a temperature change of one degree Fahrenheit from one side of the material to the other. The lower the K-value for a material, the better it insulates. If the K-value of the material is known, the R-value per inch can be determined by dividing 1 by the K-value (R-value per inch = 1/K value). The LOWER a K-Value, the better its performance as an insulator.

I think it is improper for a manufacturer not to mention K AND R values

 

[kevinmoelk]

I did read the article, twice actually. Further down in the article they give the following example:

K-Value Example: A wood stove may call for a floor which has a K factor of 1 or less. A product such as Micore 300 Board from USG has a K-Value of approx .43 per inch. Therefore a 1/2" thickness of this board would have a K-Value of .86, which meets the requirement of our example stove.

If this statement is true that means the K values and R values have an inverse relationship. As K values rise, R values fall, and visa versa. So if I require .86 K value, then I would need 2.5" of wonderboard.

1"=1.92 K value (1.92/1=1.92)
2"=.96 K value (1.92/2=.96)
2.5"=.768 K value (1.92/2.5=.768)

I'm not trying to argue here... perhaps if you displayed your math it would be more clear to me.

-Kevin

 

[begreen]

I think you're over-agonizing here. Your stove sits like what, 8" above the hearth? That's 8" of air space on top of the ashpan. This is only a medium-sized stove. K value for 1/2” of CEMENTBOARD is .86 . And then there is tile on top of it. As I said earlier, a single layer of durock under the tile is fine. The two layers of durock bring the K value up to 1.72. Get some tile on that sucker and move on.

 

[Corie]

What's more frustrating, as I said in my PM to you Kevin is that the manufacturers


DON'T PUBLISH UNITS ON THE STUPID FRIGGIN K AND R VALUES

We're to assume they're in BTU/ft^2 * DEG F * hr. But what if they're in W/M^2 K? We'll never know.

This is the equivalent to publish the length of something as 5.

five what? Inches? Feet? Meters? Kilometers? Centimeters? Pounds? Who friggin knows?

 

[kevinmoelk]

Yes, I probably am over-agonizing BeGreen. I think Corie and I figured it out, well Corie did.

Okay, enough chit-chat. Back to construction.

A big thanks to everyone for their input and suggestions.

-Kevin