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Loop length?

Parx Member Posts: 4
Hello, I have a question about the best radiant design. I have an addition that I am installing above sub floor radiant heat. I am also going to run the radiant into the existing house. I have two options:

1. All loops on the same circuit would be kept inside each room. The install would be easier, but the loops would vary more than option two. Each loop for the circuit would be 234',228,'232',284',259' and 201'. All loops include head length and are spaced at 8". I know I am suppose to be under 300' for 1/2. Also I would be installing the adjustable flow manifold.

2. All loops on the same circuit with loops continuing  into other connecting rooms, harder to install with more turns and such. Loop lengths would be closer length. 233',233',231',256',250',256'.

Basically, will the adjusting manifold take out flow issues with option 1 having the largest loop length difference at 83' or is it best to keep all of the loops within 25' and deal with more turns.

I have done heat calcs, and it does not seem to be enough change in loop to matter. All the rooms involved are open air to each other. It will cover 4 rooms.

I need to keep this on one circuit.


  • Zman
    Zman Member Posts: 7,330

    I don't think you should be using 300' as your max. The head loss and associated reduction in flow goes up exponentially as you pass the 250' mark.  I would design for loops in the 200'-220' range and consider your max 250'. This will give you more even heat and allow you to use smaller circulators.

    Balancing is also less important with shorter lengths. You will never notice a temp drop on a floor with 150' and 225' intermixed. A floor with 225' and 300' would be noticeable.

    I would recommend going shorter, add a loop to get your average around 200' and don't sweat having some minor differences.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Parx
    Parx Member Posts: 4

    Thanks for the info. Actually what I had to do was go to 8 loops. To balance 7 just made for some really short patters in rooms to get the lengths. I know 8 is over kill but, they all average about 190'. Should make for a even floor, I guess.
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    I would always

    advocate for being able to flow balance/adjust individual rooms. equal loop lengths only matter if you are not going to have balancing capabilities on the loops. and I think that is a bad idea.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
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