We are thinking of installing a 1986 Jotul #3 just in front of our fireplace. We are thinking of using a 2"x36"x36" reinforced concrete slab, that we already have, under the stove, as the fireplace hearth is not big enough for clearances. I can't find anything on the K value of concrete that I understand. I have found 2 different formulas on this site for R to K conversion. The slab is 3000 pound cement according to the maker of the slab. Thanks for any input we receive.