How to Install A Heated Floor In a Basement Bathroom?

Question

I own a split level bungalow built in 1938.

I am currently working on my plan of attack to turn a very dungeon-type basement bathroom, currently a very large 1/2 bath, into a more functional and comfortable bathroom. My first question involves heating. My home has a natural gas, radiant, hot water heat system. Can I tie into that to provide hydronic heat to my bathroom floor?

I understand this will raise the existing floor by a few inches. My research thus far has led me to believe that I need to insulate the existing concrete floor, (possibly with a layer of Styrofoam insulation) attach PEX or copper tubing to the insulated surface, then pour a new floor over this. This is not a problem as I plan to pour a base for a new shower anyway, but I wanted to be sure I had the insulation process right. So, do I need to insulate the existing floor before installing the hydronic heated floor over top?

My plan is to provide a heated floor to only the 54sq foot bathroom. Insulate and finish the walls of the entire basement and finish the rest of the basement floor in a mixture of hardwood flooring and tile. I plan to install a glass block shower. I have an existing drain line coming down from the first floor and running into the basement floor, about 4 feet from the planned shower. I plan to chisel away space for a P-trap and provide a downhill run of the new shower drain and tie into the existing line. Water supplies are readily accessible for both the plumbing and radiant heat system. Electrical is updated to GFCI & adequate for our needs, but I would like to avoid any electric based heating options.

Do you see any obvious issues with my plan?

Answer 1

Provided that the terms you use are accurate it sounds fine. Some people will confuse radiant baseboard heating with radiant in floor heating and although these are similar they operate at different temperatures. A special temperature tempering valve is required to transit from one to another.



Styrofoam is for packing. There are better similar water resistant products used for insulation, especially for ground contact. An uninsulated concrete floor is a heat sink. Without insulation it is likely that the bathroom may never feel warm as most of the heat is drawn into the ground.



A concrete shower base is not simply poured in place. It requires a liner with a double drain. The second layer of concrete is a very dry mix that is packed in place rather than poured.



How do you plan to regulate the temperature of the bathroom? There was no mention of a separate zone and thermostat.



Alternatives you might consider:

- an electric floor heating mat over a wood floor but under tile may be a cheaper option

- a radiant light fixture or a radiant electric panel on the ceiling may also be less troublesome and cheaper. http://www.thermalinc.com/comfort/cp.htm

Answer 2

Don't use any copper. That's the first thing you should avoid. Hydronic radiant heat in concrete uses PEX radiant tubing now. It will last the lifetime of the floor. The rest of your plan sounds excellent. Insulate below the concrete, pour a new thin layer of concrete with the PEX tubing embedded into the floor.

Answer 3

With the installation of copper or any other pipe in concrete floors, be sure to allow movement for expansion and contraction of the pipes, or they will shear off in concrete.

Next, give some serious thought to a vent, as once the liquid develops a air lock, without a high wall vent, you're out of luck. A pump will not clear an air lock.