Seeing as it has turned from rain to snow...AGAIN (ya killin’ me), it is a good time to turn to my heating solution.
I had originally planned on simple propane heaters in a few strategic locations. It won’t require much considering the efficiency of the structure. However, half way through the slab grading, with a little encouragement from my helper, I decided to switch to in-slab hydronic radiant heat.
OK, now I knew next to nothing about radiant heat. In fact, I had never even heard of it before reading that first strawbale book. However, I found a ton of good data on the web, but ended up on the web site of these folks (www.radiantcompany.com).
Now, here is my first endorsement. First of all, these guys offer free design services. I simply emailed my a rough sketch of my design (basically layout and dimensions), and they did the complete design, parts take-off, and quoted it to me. The design was mine for free, whether I bought from them or not. However, their prices were very competitive, and they offered free shipping, too.
Second, they offer turn keys kits. For a guy like me, that's perfect. All pre-assembled, shipped to your door, only need 3 or 4 connections and your done. I LOVE IT!
Now there are some important factors when using radiant heat. It won’t be such a challenge considering I will be using it in Tennessee. Winters (normally) are not severe. However, it is important to insulate the slab below and on the edges, since that is where most of the heat loss occurs. I have insulated mine following the example of the Red Feather manual (used in the Dakotas...much more severe winters). I have installed 2-inch rigid extruded polystyrene insulation all under the slab and around the perimeter. The 2-inch board has a value of R-10.
One thing to keep in mind in Tennessee is termite preparation. It is code, anyway, but I would have done it regardless of code. The side border insulation could especially be an issue since termites might try to come up between the insulation and the slab.
Once the insulation board is down, it is important to mark wall locations with spray paint. The reason is after the slab is poured, you can’t see the PEX tubing, and if you have laid it under the place where an wall is going it is much more likely that you could drive a nail through it. Not a good thing!
So after the board is down and the walls are marked, I set the interior slab rebar. Now this is another detail which most contractors won’t do. Most concrete contractors would put down that wire mesh for slab interiors (if anything). The problem with the mesh is when the concrete is poured it just pushes the mesh to the bottom. The whole point of the steel reinforcement is to add tensile strength to the concrete. Concrete is awesome in compression, but in tension...not so much. However, the steel does no good at the bottom of the concrete. So rather than using the mesh, I used 1/2 rebar 18-inches on center, in a grid on plastic stands, above the rigid foam. This keeps the steel in the center of the concrete, and gives you a good tie point for the PEX tubing.
When tying the PEX to the rebar, I used plastic wire zip ties instead of the standard concrete wire. This is probably overkill (I’ll admit it), but this reduces the chance of the PEX getting cut during pouring. Better safe than sorry, right.
