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steep driveway hydronic heating system

ASK
ASK Member Posts: 1
My contractor wants to do the following:
1- crushed gravel foundation matching the grade (8-10 % grade)
2- cover that layer with foam backed rolled reflective foil (not 2" of foam board, saying that it would crack and compress over time)
3- wire grid for attaching the heating pipes
4- cover to pipes with 5-6 inches of concrete

I know you prefer 2" of foam to foil.
My real question now, is 5" of concrete too thick for this system to actually work?

Comments

  • Wellness
    Wellness Member Posts: 122
    edited December 2018
    Pumps can easily handle pushing water up a grade, but your contractor should use rebar and chairs, not wire grid, which will get pushed to the bottom in the concrete pour along with your heating pipe. For a driveway 4 inches is a minimum pour, but with piping (and for heavy vehicles) I'd also recommend at least 5 inches of concrete.
  • hot_rod
    hot_rod Member Posts: 15,012
    This attached model is for a residential heating slab, 4".

    But it gives you an idea of output difference with tube depth. Do your best to gets the tube up into the pour.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    edited December 2018
    Mid depth on the tubing. Some here use the barrier. The 250 psi XPS will be sufficient so long as sub base is properly compacted. Foil face has zero benefit.
    STEVEusaPARich_49
  • Gordy
    Gordy Member Posts: 9,514
    The more concrete above tubing the more likely btus will go to ground first, especially with poor insulation.
  • hot_rod
    hot_rod Member Posts: 15,012
    A 4" slab example, deeper tube = higher required SWT for same output
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Steve Minnich
    Steve Minnich Member Posts: 2,673
    @Wellness - In a closed system, the pump doesn't care about the height of a building, driveway, or anything else.
    Steve Minnich
    Minnich Hydronic Consulting & Design, LLC
    [email protected]
    GordyRich_49
  • Zman
    Zman Member Posts: 6,966
    edited December 2018
    I have some questions for the contractor:

    Is he trying to melt snow or heat the ground?
    Keep in mind that heat does not rise. Thermal buoyancy only applies to fluids like air and water. Radiant heat is like light, it knows nothing about gravity.

    Why does he use mesh under the slab? It has no structural benefit when left on the bottom (and it will be). Not only that but the tubes then end up on the bottom and heat the ground very effectively. You are trying to melt snow, yes?

    Reflective insulation does absolutely nothing under a concrete slab. Don't waste a dime on it. There is not a single science based document to the contrary.

    A properly constructed concrete slab (not mesh laying on the ground) will spread the weight of the vehicles over a wide area and you will have no issues with compressing the foam.

    For best results use 2" rigid insulation, use real rebar on chairs and tie the tubing to the rebar at ~ mid slab.

    Do it right and do it once.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    STEVEusaPADZoro
  • Zman
    Zman Member Posts: 6,966
    Why 2 posts on the same subject?
    Very confusing.....
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Gordy
  • Gordy
    Gordy Member Posts: 9,514
    There is heavier grade road mesh. However if it is not put in right it’s still not effective at reinforcing the slab. The bottom is no place for it to effectively reinforce the slab. May as well use nothing.

    Most contractors throw it in to give the customer the feeling they are going the extra mile.....in effect it’s only giving them something to attach the tubing to where it will also be less effective at melting the snow.
  • Jamie Hall
    Jamie Hall Member Posts: 17,029
    The gravel foundation is OK -- provided it is small, well graded gravel and compacted very well -- not just dumped and scraped into position. Then your 2 inches of XPS foam. Then the reinforcing mesh must be on chairs, so it is pretty close to midslab You can tie to the pipes to that. My preference would be to use fiber reinforced concrete -- either steel or fiberglass, but I prefer steel -- as it reduces cracking considerably. Plain concrete, even with mesh, will crack..

    Stay away from the reflective foam or bubble stuff -- there are applications where it is useful. This is not one of them.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ratio
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 1,695
    Zman said:

    Why 2 posts on the same subject?
    Very confusing.....

    I've combined the two posts. Thanks!
    President
    HeatingHelp.com
    Zmankcopp