I did take a course in thermodynamics but I don't recall a discussion on R value. My guess is that as the temperature goes up, the thermal resistant goes down because the thermal gradient is higher. My guess is that saying something has a R value of... without stating the temperature is not completely accurate. I need to ask the manufacture to see what they say. I wanted a low profile hearth; I know some like a higher hearth, but I was wanting a low profile one. With inch of Micore I have a R2 plus the durarock; and a height of 1.5 inch. With the Roxul, it would be 2.5 inches; plus the tile.
Since there are so many other methods to get the required value, I'd say 21" of slab is a moot point.
I contacted Roxul and talked to a rep and was told that they did not have any sort of fire rating for the Rockboard 80 and she could not they me what the R value would be at the temperature coming off of a wood stove. It would have been cheaper than the Micore but I need to know that it will work. The woman told me that it would probably work OK in my application but that is about all. What does others think?
What I was going for in my post on the previous page- can R value be arrived at if you know thermal conductivity, which (for the refractory product I linked) is often given over a range of temps, and solve for the unknown "R"? Just wondering....
If I know the equation; maybe I can do a different search and get some info. I looked in the index of my thermodynamics textbook but did not find anything about R value or thermal resistance.
Ok Kimberly ..... Now, can thermal conductivity # be used anywhere/plugged in? I'm no math person....
Basically, as the temperature goes up, the R value goes down and that equation is linear. So Rockboard would probably be as suitable for the hearth as Micore; I would think a 1 inch board would have an R value of around 2. Micore at 1/2 inch is a bit over 1; 1 inch gives 2. If I could find the Rockboard in a 1 inch sheet then that would give me the R value I need plus the R of the durarock and still have a relatively low profile hearth.
I still think you could pour a castable refractory, top layer it with durock/tile, and be good to go... Just my $.02.
I don't know about Rockboard; but I do know from practical experience, that Micore can be cut with a utility knife. Make your line, score it, snap it, and then back cut if needed.................just like sheetrock/drywall. Where a mask or bandana over your mouth and nose though if using this product.
As an aside, my experimental rocket stove is cast with insulating castable refractory, and with a full on fire blazing in it, I can place my hand on the outside of the firebox for over an hour. 1 1/4" thick walls, hand on it for over an hour. 1000+ degree fire an 1 1/4" away... 4 foot flame out of the riser.... Over an hour... Jus sayin. Again.
I still think that Micore is the way to go for the OP. Light weight, easy to work with, and the best "bang for the thickness" regarding R values out there!!
I couldn't agree more, MightyWhitey! Phew, I was starting to get wore out on the refractory stuff any ways
Well, that's putting it.....nicely Diplomatically, even I grew up hearing it differently on the end of it
If I were closer to Kimberley, I'd go there and offer to build a hearth myself...............seeing as that I have the same stove!!!
