Radiant floor heating systems are becoming increasingly popular throughout the United States today. Radiant heating systems distribute heat "omni-directionally", or in all directions, offering greater energy efficiency than conventional forced air heating systems in which warm air naturally rises, resulting in warm ceilings but cold floors.Installing a hardwood floor over radiant heat is not much different from laying a typical hardwood floor, as long as you understand radiant heat, how it can impact wood flooring, what precautions to take, and what type of wood flooring to use.
Understanding radiant heat: Radiant floor heating systems consist of tubing installed under the finished floor that is responsible for delivering heat through the floor and into the home.
Impact on wood flooring and precautions to take: One of the most important factors in a successful wood flooring installation over radiant heat is a dry slab and a dry subfloor. This is important in any wood floor installation, but particularly over radiant heat systems, because once the radiant heat is turned on, any excess moisture in either the concrete slab or subfloor will be directly transferred to the wood flooring. Any moisture entering a wood floor in this manner will cause severe problems to the floor (swelling, buckling). To ensure that all moisture is removed prior to the wood flooring installation, the radiant heating system should be turned on and run for an extended period of time (the National Wood Flooring Association recommends 5-6 days) to remove any residual moisture.
Choosing wood flooring: According to the National Wood Flooring Association, wood floors best suited for installation over radiant heat include engineered wood floors, solid woods that naturally have good dimensional stability, and solid wood floors that are no more than 4" in finished width.
Choosing wood flooring: According to the National Wood Flooring Association, wood floors best suited for installation over radiant heat include engineered wood floors, solid woods that naturally have good dimensional stability, and solid wood floors that are no more than 4" in finished width.
Now that you are ready to install your radiant heating, here are a few ways to set up the system:
Direct Nail to Subfloor over Floor Joists:
A popular set-up in which radiant tubes are strapped onto a plywood subfloor laid over the floor joists. Wood flooring is then nailed to the plywood subfloor.
Note that a moisture barrier should always be placed over the subfloor to which the wood flooring is nailed. A good choice is #15 felt paper.
Note that a moisture barrier should always be placed over the subfloor to which the wood flooring is nailed. A good choice is #15 felt paper.
An approach used when you do not have access under the existing subfloor or when the underside of the floor cannot be used. Here the radiant tubes and sleepers are laid on top of the existing subfloor, and a second subfloor is added. Wood flooring is nailed to this second subfloor.
Solid T&G Floor Direct Nail to Sleepers: 
This set-up involves laying sleepers over the subfloor and radiant tubes between the sleepers. A vapor barrier is installed over the sleepers and wood flooring is nailed directly to the sleepers. Some individuals also choose to put a gypsum or concrete mix around the radiant tubing, which provides fire resistance and sound dampening.
Single or Double Layer of Plywood on Sleepers: 
Similar to the approach above, except a layer of plywood (or even 2 layers) is applied over the sleepers. The wood flooring is then nailed to the plywood.
