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Radiant slab pipe spacing

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scott markle
scott markle Member Posts: 17
in THE MAIN WALL
Basements generally don't require as much heat as other parts of the house. My feeling is that tube spacing is really not going to have a significant impact on the cost of your project. You can probably get away with 12'' spacing especially if you do a counter flow or reverse return (same thing) arrangement. If you can plan your layout carefully and place your manifold centrally you might be able to make your circuits lengths close enough in length to avoid the cost of a balancing manifold. Remember to bring the spacing to 6'' at the perimeters of the slab. I prefer multilayer pipe with an aluminum oxygen barrier such as viega fostapex 1/2'' or 5/8'' dia. around 300' to 350' max. a bit shorter if a serpentine layout is used (as opposed to counter-flow). Counter-flow layouts can be tricky though. Consider making a scale drawing of your slab and scale lengths of string to represent tubing (based on a length that divides nicely into stock coil lengths). You really need to understand how to calculate flow rates based on anticipated heat requirements and the potential heat delivery of the floor surface. The 25 btu/sq. ft is in the upper end of what you should expect from floor heat. Remember gpm=btu/500xdeltaT . In my opinion a slab without radiant heat is a missed opportunity, there is really no comparison to radiators. Especially in a basement were it will counter the clamy moisture condensation feel that these spaces often have. If it's done right it will certainly cost more than radiators, but it's probabaly the controls, manifolds and pipe work that will cost. Good slab heat should be controlled by an weather responsive heat curve. Not conventional one temperature on/off circulation with an indoor t-stat. This is because of the inertia of the thermal mass in a slab. I would prefer to tie to wire instead of foam clips although I'v never used the clips.

Comments

  • Dave_4
    Dave_4 Member Posts: 1,404
    I know it's in the books, but . . .

    I am just trying to get a cost difference between heating space that is on a slab on grade with infloor piping versus using radiators.

    4" slab in basement, will insulate with 2" rigid foam underneath, maximum heat loss in any space would require a little under 25 Btu/h emittance from slab.

    Recommend us a diameter and spacing, please.

    If we pipe it, we are torn between tying it to 6x6x10/10 mesh, and using barbed staples to fix it to the foam. Using the mesh precludes any spacing other than on 6" modules.

    Do the staples work, given the rough treatment the folks doing the pour might give things?
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Trying to sell a cow in a free milk market

    Too many varibables as to number of circuits, length, water temperature and so-on... Could be 8 inches to 12 inches. Could be 6 inches or 7 or 10....


    Do yourself a favor. Go to the online store and buy a Rad-Pad. All of the What-Ifs you could ask for and educational too. Best $30 you can spend next to buying a brick or three. Yes that is a hint :)
  • ALH_4
    ALH_4 Member Posts: 1,790
    and...

    In addition to Brad's recommendations, I would also recommend purchasing a copy of Modern Hydronic Heating. You will not find a better reference.

    7" oc? The installers would kill you. I find that if the spacing is not at least a multiple of 3 (usually 6, 9, 12, 18, or 24), the people laying out the tube are unhappy. ;-)
  • scott markle
    scott markle Member Posts: 17
    slab pipe spacing

    Basements generally don't require as much heat as other parts of the house. My feeling is that tube spacing is really not going to have a significant impact on the cost of your project. You can probably get away with 12'' spacing especially if you do a counter flow or reverse return (same thing) arrangement. If you can plan your layout carefully and place your manifold centrally you might be able to make your circuits lengths close enough in length to avoid the cost of a balancing manifold. Remember to bring the spacing to 6'' at the perimeters of the slab. I prefer multilayer pipe with an aluminum oxygen barrier such as viega fostapex 1/2'' or 5/8'' dia. around 300' to 350' max. a bit shorter if a serpentine layout is used (as opposed to counter-flow). Counter-flow layouts can be tricky though. Consider making a scale drawing of your slab and scale lengths of string to represent tubing (based on a length that divides nicely into stock coil lengths). You really need to understand how to calculate flow rates based on anticipated heat requirements and the potential heat delivery of the floor surface. The 25 btu/sq. ft is in the upper end of what you should expect from floor heat. Remember gpm=btu/500xdeltaT . In my opinion a slab without radiant heat is a missed opportunity, there is really no comparison to radiators. Especially in a basement where it will counter the clamy moisture condensation feel that these spaces often have. If it's done right it will certainly cost more than radiators, but it's probabaly the controls, manifolds and pipe work that will cost. Good slab heat should be controlled by an weather responsive heat curve. Not conventional one temperature on/off circulation with an indoor t-stat. This is because of the inertia of the thermal mass in a slab. I would prefer to tie to wire instead of foam clips although I'v never used the clips.
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