The issue comes down to the possibility that warm floor temperatures during the heating season will cause unacceptable shrinking of the hardwood. And though you should check with manufacturers specifically about warranty issues when installed over infloor heating, I don’t think you’ll have trouble. The best engineered hardwood flooring is made with a thin layer of high-quality hardwood on top of a laminated plywood substrate made of less valuable species. This laminated construction makes engineered flooring much less prone to seasonal expansion and contraction, especially over a heating floor. Even solid wood floors typically perform surprisingly well over infloor heating installations. In tests I’ve conducted using shrink-prone white pine flooring, shrinkage rates were acceptable even when repeatedly heated to the 90ºF levels typically found in heated floors running full blast. Click flooring is even better than traditional, nail-anchored wood flooring when applied over infloor heating. That’s because any expansion and contraction of the flooring happens at the edges of the room, where it won’t be seen underneath baseboard and quarter round.