I'm in the process of building a 16x26 garage on a thickened edge floating slab, at my cabin in Northern MN. I have 2 inch F250 under slab and 2 " F150 around perimeter. Tubing is 1/2" barrier Pex 12" OC, 2 loops @210 ft each. Walls will be 2x6 R19, 9' ceiling R38. I am told I need around...