Hydronic Pipe in Concrete Slab

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Spaceman Spiff, Dec 8, 2005.

  1. Spaceman Spiff

    Spaceman Spiff Architect

    Messages:
    277
    Location:
    Salt Lake City, Utah
    I am about to have a slab poured on the North side of my house for the driveway in snow country. Has anyone dealt with hydronic snow melting? I want to install the tube now and have it available for when I can get to the heater portion. I understand I need to use the 0-2 barrier type PEX and run the tube 6" apart. Anyone have any more insight or tips on what I need to do? Thanks!!!

    In case it matters it is a 20x30' slab, 4" thick and gets down to 0°F regularly in Cedar City, Utah.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    There's a lot to engineering a successful heated slab outside. Proper insulation and moisture control (wet soil decreases the efficency significantly), proper flow (you may need a manifold system rather than just a single serpentine run). Then, there is what class system you want: 1, 2, or 3. If I remember correctly, class 1 means snow can accumulate, but it will melt eventually; 2, melting occurs regardless of snow load, but some might accumulate; or 3, hot enough to keep snow off, regardless of the rate (often used around hospitals, etc). To do it right, with minimal operating costs, it has to be sized and installed properly. Depending on the size of the tubing, that spacing might be excessive or too far apart. Adding moisture sensors, temperature sensors, mixing valves can all make it more efficient. There is no need to heat the slab on a very dry day, no condensation to freeze, etc. I've never installed one, but I looking into doing it once for my condo complex (we have a significant hill). Couldn't talk them into it.

    Also, you may need a heated drain to dispose of the moisture - you don't want the liabilty of meltwater running into the street and freezing - very bad idea. As is it creating an ice dam at the side of the driveway. It can make the walk to the sidewalk very challenging. Get help from someone who specializes in this is my unprofessional opinion. You can glean some good info from the web, as that is where I got most of mine - don't remember the manufacturers sites I tapped, but google will come to the rescue. Most of the companies that do in-home radiant heating have sections that deal in snow removal - check them out.
  3. Spaceman Spiff

    Spaceman Spiff Architect

    Messages:
    277
    Location:
    Salt Lake City, Utah
    Street, What street???

    I don't have to worry about the street, the closest asphalt is about a mile away... The water when it melts off the concrete will go to a drainage ditch. No worries there, mate! I was searching the net for information and all I found was that the insulation was optional, you attached it to the 6x6 remesh, and that you pressure test it before, during, and after the pour.
    All I am looking to do is get the tube in place (last minute before the pour) otherwise I'll probably regret not doing it...
    Right now, unless I get other advice or find somethin' new on the net I think I'll get a 1000' spool of 1/2" PEX and do for zones and run them back to the garage.
    Thanks for looking and for the responses. Cheers!!!
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    Depending on the shape of the slab, rather than loops, you may need a manifold on each side with pipe going between them. Otherwise, you'll end up with the beginning of the loop melting things, and the end of it not. Also, keep in mind that you'll need antifreeze. This decreases the heat transfer by about 10% unfortunately. Unless you use a heat exchanger, your entire system (unless the boiler is dedicated to the outside slab) will be derated by about 10% as well. Most people have excess capacity, but keep that in mind. Last (I can think of, but I'm not a pro), some boilers can't stand the thermal shock if the return water is too cold, so sizing things properly is very important.
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