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Radiant tubing formulas?

Thaddeus
Thaddeus Member Posts: 40
Hi, so in my previous post I asked about appropriate media's for outdoor radiant applications. Now that I have gotten good sense of what I am willing to try; are there any formulas or general guide lines about choosing the tube size and lay out pattern per a given media? For instance I think that tubes might be closer together in a fine granular media then in concrete. And is there a reason to choose a wavy pattern over a circular spiral like pattern? Are there limits to a length of a given run for heat dispersion or should I plan on a manifold with multiple pumps and different sections (areas) of the ground I choose to install radiant heat in?

Thanks for any reply offered

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 18,943
    Generally the tubing is run in a rectangular grid -- say anywhere from 8 inches to a foot (or maybe a tad more). The reason I suggested a shallow wavy pattern was to allow for easier expansion and contraction and movement as the medium it is in moves...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Thaddeus
  • hot_rod
    hot_rod Member Posts: 16,310
    snowmelt systems are somewhere in the 100- 250 or more btu/ square foot. 3/4 or larger tube 9" oc or less.

    I'm not sure about outdoor radiant heating? most often outdoor radiant is a snowmelt design and ASHRAE has guidelines based on snowfall amounts and how quickly you want to melt.

    Critical applications like landing pads at hospitals may be designed around 250 or more BTU/ ft. No accumulation or striping allowed.

    The large melt pads at airports design around those numbers also.

    It is rare to see a residential snowmelt system much less than 100 BTU/ft.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Thaddeus
  • hot_rod
    hot_rod Member Posts: 16,310
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Thaddeus
  • Gordy
    Gordy Member Posts: 9,514
    That is a very informational link @hot rod provided.
  • Gordy
    Gordy Member Posts: 9,514
    edited April 2017
    Next is the universal hydronic formula :)
    Thaddeus
  • Gordy
    Gordy Member Posts: 9,514
    In using the formula you will see it won't take a lot to use that 240k. Depending on which level of snowmelt, and number of square feet you choose to do.
  • Thaddeus
    Thaddeus Member Posts: 40
    Thanks for all the advice and links! I will be putting them to good use!

    Gordy, You are correct, my initial calcs show that I might be in the 300k btu range needed, BUT I plan on running this manually, not automatic. When I want to clear the snow, Ill load the hell out of the boiler it let her rip!
  • hot_rod
    hot_rod Member Posts: 16,310
    Snow melting generally happens during heating season, and maybe at design conditions. So you only have available to melt, what the home doesn't need.

    So maybe only install that amount of outside snowmelt, or zone it to do small portions at a time.

    Remember also, melting snow is a slow procedure with the amount of BTU you have available. Be realistic in your design and expectations
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GordyThaddeus
  • Thaddeus
    Thaddeus Member Posts: 40
    My expectation is that I will snow melt only at night, so I can load the boiler full and allow it a good 12 hour run. My boiler has 2 circ loops. One is the house and the other is the garage. But they are first use in their respective loops, so any other heating application I install will come after those demands are met.
  • Gordy
    Gordy Member Posts: 9,514
    Anticipating the load, and getting a head start is an advantage. So long as the weatherman is right :)
  • j a_2
    j a_2 Member Posts: 1,796
    I believe the RadPad is still available. On this site....it's a very useful and gets you pretty close
  • hot_rod
    hot_rod Member Posts: 16,310
    Gordy said:

    Anticipating the load, and getting a head start is an advantage. So long as the weatherman is right :)

    A wi fi control for snowmelt, allows you to remotely start or view operation.



    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    Those are sweet. So long as you have cell service.