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heatin guy

Anyone have issues with radiant heat in a 6" concrete slab "OVERHEATING" ?

The tubing was laid out by one engineer who is no longer on the job, 12" centers through out, 12" insulation under the slab!!! The boiler will have outdoor reset and t stats will have a 5degree anticipator.

The new engineer wants to abandon the tubing in 6" slab and install new tubing on top in a thin slab. He believes the thermal mass of the 6" slab will cause the rooms to overheat. Any suggestions or comments greatly appreciated


  • Ironman
    Ironman Member Posts: 7,224
    edited February 2012
    Slab Over-heating

    A high mass emitter like a slab needs to be controlled by outdoor reset that will vary the water temp to match the load. When it's installed and adjusted properly, the thermostat will act more like a high limit: the reset control will maintain the comfort level.

    There are two methods that are used to accomplish this: a smart mixing valve or variable speed injection mixing.

    Putting another slab on top of the first one will not resolve the issue: it's going to back heat the lower slab unless enough insulation is placed between them. It would still need to be controlled by outdoor reset even if there is a layer of insulation placed between them. I can't see the benefit of a thinner slab on top of what you've got now.

    If you have a mod/con boiler, and if it only has to supply one water temp to the zone(s), then its reset control can be set to accomplish this. If you need multiple temps, then the slab needs its own reset control.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Zman
    Zman Member Posts: 7,496
    How hot?

    Iron man is absolutely correct. What temp water are you sending to the floor? What kind of outdoor temp swings do you get? Solar gain?

    The outdoor reset should work well unless you big swings or solar gains.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kcopp
    kcopp Member Posts: 4,305
    Give us....

    some more detail. Boiler? Fuel? Piping? Tube size? Pictures? How is it controlled?
  • Should be OK

    In my book, 6" is the maximum slab thickness for tubing installation along with a outdoor reset system.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
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