As part of a master bath renovation, we had our contractor install one of those Nuheat electric heating pads under the tile floor and we can adjust it through a controller on the wall. The rectangular space available for installing such a pad is an absolute maximum 39" x 84", so I was puzzled to see an empty box for the unit showing the dimensions as 60" x 84" (even though many sizes are available, including 36" x 72" which would have been fine). That would indicate to me that part of the unit extends under the heavy double vanity and marble countertop. It not only seems wasteful to use an oversized pad and heat the underside of the vanity. I'm also concerned that the pad isn't meant to hold the weight of the vanity and marble top. Is there any reason to be concerned? Thanks.