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Forced Air Radiant

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Ed Lentz_2
Ed Lentz_2 Member Posts: 158
Our first house was a slab, within the slab they laid 8" blocks on their sides and used a forced air furnace to do the heating. The ONLY warm place in the house was RIGHT over the 'tunnel'. Before we left that house, we put in registers, but it still was damn cold!

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  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
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    Forced Air to heat the concrete slab

    I have a customer interested in a system which provides radiant heating by using hot air ducts which are cast into the concrete slab.Since I have zero experience with this type of heating system can you please give me your thoughts on this system.I can't imagine why you would want to do radiant this way when you can use lower temperature water in radiant tubing. You can check it out at www.legalett.ca
  • GMcD
    GMcD Member Posts: 477
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    Another spin on Tarmac/Termodeck

    But using air as the heat transfer and energy transport system is very inefficient and no where near the overall energy efficiency of a hydronic system. See the Termodeck website for using hollowcore concrete planks as part of an air distribution/thermal mass radiant systems:

    http://www.termodeck.co.uk/termodeck_index_page.htm


    This may be a spin on the labour saving for not having to lay a lot of PEX around, but at the penalthy of on-going operationg costs.
  • Tom Manton
    Tom Manton Member Posts: 30
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    Did an air core slab one time in a passive solar house mostly for heat extraction.

    Laid 6" cored concrete block on its side lining up the cores, the poured 4" slab on that


  • ah, ancient roman technology at work.

    We've improved upon it since then.
  • Dave Yates (GrandPAH)_1
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    I came across

    exactly that in an old engineering book my uncle gave me before he engineered his way to the other side of the lawn. I scanned the drawings for a Power Point presentation & have them on the home computer. In them, they detail sub-slab as well as wall and ceiling forced hot air radiant. The text discusses all the same things we do when considering wet heat - like MRT and how to calculate to keep that at or below 85F. The more things change, the more they stay the same!
  • Stew_5
    Stew_5 Member Posts: 23
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    In 1959 my Dad built his office in northern PA. It's about 24x32, single storey with a crawl space underneath. The forced air furnace just blows into the crawl space with a few vents in the floor. No ducting. The floors are always warm and the room is very comfortable. I wouldn't want to try it with a slab though.
  • Mike Lampkin_2
    Mike Lampkin_2 Member Posts: 124
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    Thanks Geoff

    for confirming what I thought. Why do it any other way when you can use something much more efficient,


  • I've seen it in an active solar house. They laid down large rock and poured the slab over that. They used a furnace to circulate the air from the living space through the solar panels, down through the air spaces in the rock and back up into the living space. So it warmed the floor but also stored heat in the rock. The furnace acted as supplemental heat. Seemed to work OK. They also had a wood stove just in case. It's been so long sindce I've seen it it's hard to remember the exact configuration of the ductwork. I think there were some dampers involved to cut the air to the solar/slab when the furnace called in as second stage but I just can't recall. I added A/C to this, it was interesting, that I recall. ;)

    No wait, I do remember, the PULLED the air from the space through the solar and then the slab. They had dampers that would close that part off and open a separate return from the space upon a call for second stage. So they drew their return up through the slab when the solar was operating.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Here's a scan of an advertisement I have for just such a system. Believe they were mainly used in the late 1950s and early 1960s.

    Actually kind of interesting. The supply was directed around the perimeter with the return coming through the center. I have no idea what methods were used to cast the thing. Same advertisement mentions an "alternative" (less expensive) method with just the perimeter supplies, registers into the rooms and unducted (I presume) return to the furnace.
  • I ran up against

    a Legalette system once. If something should get-in there, how would you get it out? Also I would wonder how the "fan box" maintenance compares to a 15-58 too?

    Dave


  • > a Legalette system once. If something should

    > get-in there, how would you get it out? Also I

    > would wonder how the "fan box" maintenance

    > compares to a 15-58 too?_BR__BR_Dave



    Good point, some small animal gets in there and dies the smell will drive you out and there'd be no way to find it and get it out of there.


  • Good point, some small animal gets in there and dies the smell will drive you out and there'd be no way to find it and get it out of there.
This discussion has been closed.