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Hot air radiant floors?

Devan Member Posts: 138
I ran into a Legalett floor system today.Basically owner has a WM ultra mod/con with two zones, each zones feed two Legalett water fan coils. The fan coil is encased in concrete slab, from there multiple 3" ducts run thru the slab and heat the slab directly.I question this method, especially since hi temp fluid to fan coil, when most likely low supply temp water could have done the job, and make better use of the mod/con.However owner seems happy with system, DIY, I was just there to figure why hot water not going to fan coil, and why fan coil blower not coming on. Normally I would not get involve, but he's a designer/project manager that I work with.<a href="http://www.legalett.ca/Story.htm">http://www.legalett.ca/Story.htm</a>


  • Yes Devan,,

    I`ve ran across this a few times in my area.

    It`s a series of hot-air ducting placed below the slab/ or within, that circulates the warm-air heated by a coil.

    To me,,, large voids under a slab/or within, are not a good thing,,, what happens if some "critters" gain entrance somehow?

    Apparently this is quite expensive an install,, but some around here have fallen for-it,,

    just another company competing in the radiant market. :-) 
  • Devan
    Devan Member Posts: 138
    What I cant figure

    is where does the air come from? I did not observe any intake or grille at the fan coil.
  • As far as I know,,,,

    without checking the website, it`s installed atmospherically and and somehow sealed.

    "That" original-air is constantly circulated through the coil passing itself-on (heated) through the duct piping network.

    A VERY strange system to me indeed,,,, I would think it would have to be pressure-tested also,,,,,,,,
  • Gordy
    Gordy Member Posts: 9,546
    edited December 2009
    Control strategy

    Wondering the time difference to bring a cold start slab up to temp verses radiant.

    Then wondering the difference is in controling the floor temp. At the very least it certainly can not be as efficient as RFH.

    Also would like to see the ducts if any left in 50 years. I guess if encased there would be the concrete ductwork. 

  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    Gee was good enough for Ceasar

    This was how the romans heated, is that not cutting edge? The customer is happy because they do not know how much fuel is being burnt to heat that air and move it around.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Devan
    Devan Member Posts: 138

    minimum 8" of concrete to cover ducts.

    I remember something about 140* F max temps in concrete to minimize cracking. 180*F going through fan coil, not what sure temp is being blown into concrete.

This discussion has been closed.