So we are installing a Quadrafire Explorer III. We have an existing built-in hearth pad. It is flush with a wood floor and measures 44" wide and 36" deep, the bricks are a red, smooth brick that is 5/8" thick (which is flush with the floor). There is a crawl space under this flooring. We need to have an R Value of 1.06 for this stove and the Quadrafire manual says hearth should be 35 3/8" wide and 39 3/8" deep. Our question is... how does this existing pad calculate into our new pad we are building. We have already purchased 1/2" Hardibacker 500, 1/2" Durock, and we have slate tiles to go over the top. We are planning to build the pad 60" wide and 58" deep. Thank you for advise and input!