Radiant Heat Under Wood Floors - Use Hydronic Radiant Heat
The best way to incorporate radiant heat under wood floors is with a hydronic system. This system involves attaching a tubing circuit to the subfloor. The room heats up when warm water circulates through the continuous tube circuit. The tubes connect to a central location called a supply manifold which in turn connects to a boiler or water heater. This is system is similar to an electrical junction box.
The loop starts when the water exits the boiler, runs through the tubing circuit which heats up the floor. The water returns at the end of the circuit to go back into the boiler to be heated up again.
There are two ways this tubing is put in the floor. First is you actually embed the PEX radiant tubes in concrete. You lay them down, and pour concrete over the tubes hiding them within.
The second way is to put them on a subfloor. The tubing rests on aluminum that is strapped to the subfloor. Aluminum is an excellent conductor of heat. You don't have to have a large thermal mass to use radiant heat. Actually, a smaller thermal mass is much quicker to respond to your heating needs, and a wood floor that is heated with an hydronic aluminum subfloor heats more efficiently.
Another benefit of radiant heat under wood floors is it is better for the wood. The natural humidity of the house doesn't fluctuate as much from season to season with radiant heat. With less fluctuation of humidity, wood floors don't expand or contract as much. This means they stay the way you installed them.
With a traditional heated forced air system, the burning of the furnace reduces humidity. With a dryer home, wood will contract. Then in the summer when the humidity levels are high, the wood expands. In the end, wood can either buckle or contract too much leaving noticeable gaps.
Types of Hydronic Systems for Radiant Heat Under Wood Floors
There are three different systems that can heat your wood floor. I don't recommend putting wood over a concrete radiant system, so I didn't include a review on this method. The strategies covered here all involve having aluminum plates wrapped around the tubing circuit. Is it possible to do this? Yes, but you'll have to float the wood floor above the concrete, and you should use engineered wood flooring instead of solid wood.
With all these methods, there needs to be insulation below the subflooring. This will ensure that the radiant heat is going up into the home instead of wasting radiant power down. The best method, but probably the most expensive, is using a Warmboard radiant subfloor. This can only be done when you are doing new construction.
The aluminum plate covers the entire subfloor with Warmboard. The hydronic system rests right in a precut groove. Warmboard suggests you use PEX aluminum PEX tubing to rest in the aluminum groove. This system is the least labor intensive. If you know how to put down a subfloor, you can lay down Warmboard.
Once the Warmboard subfloor and the hydronic system is in place, you simply cover the floor with hardwood. Just be sure to watch where you are nailing so you don't puncture the PEX tubing. This product is used for some of the most efficiently heated homes in the world.
I really believe that this product will be used more and more as people see how simple and amazing it really is. You have to buy this material direct from the company, but you can contact them and they will be more than happy to answer your questions. You can read an interview that Radiant Heat Reviewer did with the Warmboard Sales Manager right here.
The other two methods involve installing heat transfer plates into the subfloor, or directly below the subfloor.
One way is to place heat-transfer plates above the subfloor. In between the hydronic tubes will be 3/4 inch plywood sleepers. A 3/8 inch plywood cover sheet will be placed over the sleepers, aluminum heat-transfer plates, and tubing. Then the floor is ready for your final hardwood placing.
The easiest way to retrofit hardwood flooring is to place the aluminum heat-transfer plates underneath the subfloor. The heat tubing is cradled by the plates that have to be attached between the floor joists. The downside to this system is it is the radiant heat source is the furthest away from the actual finish flooring.
The further away the aluminum gets from the finish flooring, the less efficient the system will be. However, all these radiant heat under wood floor systems are still more efficient than heated forced air. Also, they all produce a comfortable source of heat.
The Best Types of Wood Flooring for Radiant Floor Heat
The most versatile option to incorporate radiant floor heat with a wood floor would be to float an engineered wood floor over a subfloor or even concrete. There are three reasons why this floor choice is the least troublesome.
First of all, it isn't attached directly to the floor, so it can expand and contract as a whole instead of one piece warping or buckling on you. Second, you are using an engineered wood, and the plywood underneath the finished flooring doesn't expand or contract as much as a solid piece of wood. Finally, you can use this option over a concrete radiant floor.
The second option is engineered hardwood that is directly attached to the subflooring. It doesn't expand or contract as much as solid wood flooring, but it can only withstand a few times being sanded and refinished.
The least common option, but it is still my favorite, is to go with solid hardwood. You can make this work if you make a few important decisions right away with your hardwood choices.
You can choose wood that has been "quartersawn" What that means is they saw the wood so the grain is vertical to the long strip of wood you have. With wood cut light this, it won't expand or contract as much. You won't be able to buy this type of wood typically prefinished though. You'll have to install it unfinished and then pick the stain color along with the polyurethane finish.
The second way to ensure your solid hardwood will do well with radiant heat is to pick types of wood that adapt well to radiant floor heat. The top choices include bamboo (which is actually a type of grass - but harder than many types of wood), Oak, Teak, American cherry, American Walnut, and Mesquite.
One final option would be to use reclaimed or antique wood. These produce incredibly beautiful floors, and they are more stable than fresh cut would. These woods have already been used in old factories, log cabins, or barns, and have endured frigid winters and sweltering summers. They have been through countless cycles of expansion and contraction, so no need to worry about radiant floor heat making them warp.
I am a huge fan of wood floors over hydronic radiant floor heat. One more tip, make sure to keep the temperature will be even at a very comfortable 80 to 85 degrees at your feet to prevent any unneeded problems.
The G and S Wood Floors.
Bamboo Floor and Radiant Heat
Radiant Water Heat
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