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first radiant floor questions

Al K._2
Al K._2 Member Posts: 27
my first prospective radiant job, and of course it's not an easy one, at least for me.

40' X 80' "barn". 29' to the peak. two multi-level, open concept lofts, one each end.

I ran a heat loss using HVAC-CALC.
First question, is this software good for radiant applications?

The calcs, and using my "RadPad", indicated too high a surface temp. Note this space is for recreational use, his business's office on one of the lofts, basically unheated garage space below (he'll use a pellet stove).
Questions... How to handle multi-level, open lofts?
... Can I add heat to the loft floors, and walls of the main floor, to offset the lack of floor for the "envelope".

Can the radiant floor in a large open room be zoned to allow usage of only one end, or say, the office loft. Seems possible, radiant heats people, not space, no?

Al K.


  • Ted_9
    Ted_9 Member Posts: 1,718

    The rad pad can help you. Did you get the Slant fin 2 free heatloss program? I does radiant design and its free.

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  • Al K._2
    Al K._2 Member Posts: 27

    no, i've got the older version. i'll check into that. thanks for the tip.
    Al K.
  • Brad White_128
    Brad White_128 Member Posts: 7
    Radiant Barn

    Just curious, Al, what kind of BTU values you are getting (with any program and to compare) as well as the "BTU per SF" densities?

    You most definitely can zone the lofts separately. As with any radiant system you must insulate underneath to a high degree (R-19 seems to be the default but can vary) to "drive" the heat upward through the floor assembly but as importantly, so as not to provide an unwanted radiant ceiling to the space below.

    ALL of the radiant floor goes to your quotient. Just make sure that the lofts themselves have heat output proportionate to their space heat losses.

    Radiant does heat people (we as beings pick up on the IR waves), but it also heats objects which will re-radiate over time, once warmed, to other colder objects and surfaces. It is not as effective at warming air for air does not absorb nor reflect IR radiation well at all.

    Yes, you can "radiate" the walls but just one of those things whereby you may increase the heat loss by driving up the delta-T on those surfaces. What I am saying here is, yes you can do it but the wall insulation has to be excellent both in R value and integrity. And how does one tell future occupants not to drive nails to hang pictures at will?? :)

    I think your tack of double-checking the heat loss and getting a second opinion is wise. When your gut tells you something, you listen to it. That is your experience talking obviously.
  • hot_rod
    hot_rod Member Posts: 21,866
    Confused abut the \"open loft\" concept?

    If the lofts are open to the lower level and not isolated by an insulated or glass structure.. probably not going to be able to maintain a comfortable temperature.

    Either add some heat to the garage area below or insulate and seperate the loft envelope from the garage.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Al K._2
    Al K._2 Member Posts: 27

    I got a value of 153K btu heat loss. BTU/SF is near 48, syrface temp at customer-spec'd 70* (i'm still talking to him about air temps) near 95*. Lots of glass way up high, it'll be a nice place when it's done for sure, but first impression is it may need supplemental heat... but i'm still checking into that.
    Al K.
  • Al K._2
    Al K._2 Member Posts: 27

    Sorry for any confusion... Lofts are open to the main floor, the conditioned space. The garage area is "basement" level. Customer plans on pellet funace for the garage area, which should help with main floor losses, but I don't think I can guarantee it's use. A clause to the contract perhaps, I'd rather be sure though.
    Al K.
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