In the video below, you will see the process to install radiant heat tubes in your concrete slab. Or rather, MY concrete slab. After you fill in stone and sand and drainage piping, normally you just pour concrete. However, if you want radiant heating there are a few steps in between.
I installed some drains in the video, however that is NOT part of radiant flooring, just something nice to have. (the first one is a drain that was an afterthought)
Steps:
- Install a vapor barrier
- Install Insulation
- Install pex tubing
Sure seems simple eh? Well it is, but there are lots of decisions surrounding those things. Read on.
Vapor Barrier
The vapor barrier is installed to block and moisture transfer between the slab and the earth. Water could go either way, either from the slab curing, or from the ground expelling water, which it will always do for ever and ever. Some people might argue it’s not needed, but as you’ll see it took about 10 minutes to install and was less than 100 bucks. meh. Just do it.
Insulation
Insulation blocks the heat you’re putting into your floor from going into the ground. Especially around the perimeter of the foundation it keeps the heat from escaping into the atmosphere as well. There are two schools of thought regarding insulating a slab. You insulate underneath the entire slab, or you insulate just around the perimeter of the slab. The latter lets heat escape into the earth and warm a fairly large section of soil under the slab to use as a heat sink. This allows a building to last a little longer when heat is no longer being provided as it slowly pulls from this big reserve tank.
As i’m writing this, i was just thinking it would have been cool to insulate about 4 feet under my slab then continue filling it in and just pour the floor on top of the stone, and use that mass as a heat sink… Darn.
In my project i used 2in rigid foam insulation on top and 1 in on the bottom.
Damn, I also just now realizing writing this, that using 2in on top was kind of uneeded, as the entire mass under neath will be somewhat heated by the space below it. Well no entirely but half anyway, although I do have some insulation along the inside of that wall, so perhaps not. NOTE TO SELF: write blog entry before doing the work so that you can do your project right.
Tubing
The tubing I used was this.
It was great to work with. Which means it stayed pretty flexible, I didn’t have any kinking issues, and yet still seemed durable. I’ve work with some stuff that kept kinking, or was impossible to bend, so this was a nice change.
Tubing layout is a whole post on it’s own, so I’ll just paraphrase. 1/2″ pex shouldn’t be run over 300 feet. The simple answer is by the time hot water has run through 300 feet of 1/2″ pipe it’s cold. If you have 600 square feet to heat, it has to be done in two 300 foot loops or circuits. In my case I had a 20 x 24 floor so I had 480 sq ft, which ended up being two 240 foot loops. I’ll tie these into a header later which is either a simple 3/4″ pipe with 1/2″ ports off of it, or a fancy one pre-built for being a header, with flow control etc.
I used these foam staples to hold the tubing down to the styrofoam. I put the staples about every 2-3 feet. I didn’t pre-fill my tubing with water, so it all had air in it, which would want to float. The staples are also cheap enough that it seemed like it just made sense. Having a tube float would be a major bummer as it would stick up near the surface of the floor.
They also make a tool for attaching these staples to the foam. It’s 200 bucks now, used to be 300, but I just didn’t see it worth the cost for the one project. Although at this point i’ve installed close to 1200 of these, including my house and this garage. Generally I’m a person who will buy a tool knowing that i’ll use it in the future and it’s an investment, but this tool can only ever be used for this one thing. I dont like tools like that. Boo.
After the staples were set, it’s ready for concrete.
So before getting started I remembered that managing a 1000 ft roll of pex was a disaster when not bound somehow. I fought with the first roll and said never again. This time I made a spool around it before I ever cut the straps.