I am putting in a radiant heat floor in a 40x70 shop with a 4" slab. I ran the heat load calcs and I will need about 28kbtu. I can't decide if I should go with 1/2" pex or 3/4" pex. If I go with 1/2", I will need 9 zones (12" spacing). If I go with 3/4", I will need 5 zones (16" spacing)...