A: The ideal hardwood floor for a radiant heat sub-floor application is a glue-down installed engineered hardwood floor. Glue-down engineered hardwood floors are made using a two layer technology that counteracts wood's tendency to expand and contract with changes in humidity. In a radiant heat application, the sub-floor exerts tremendous pressure on the wood floor as the heat permeates through the floor. Therefore, the hardwood will experience advanced expansion and contraction. Engineered hardwood flooring was designed to counteract this additional pressure where solid wood cannot.