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Do I need to increase the size of my boiler piping?

Joe107
Joe107 Member Posts: 23
I have a hydronic system with 12 zones each fed by .5" pex coming off of a 1.25" copper manifold. The 1.5" output on the boiler was reduced down to 1.25" and 1.25" copper piping was used for the supply and return lines between the supply and return manifolds and the boiler. I am going to be adding a .75" pex loop for baseboard radiators in my basement. I am planning to install a tee into the supply piping for the basement zone before the manifold. With adding this new zone, should I re-pipe the boiler using 1.5" pipe and reduce to 1.25" between the new tee for the basement and the existing manifold? I don't want to do all this work and then have inadequate water flow when multiple zones are calling for heat. Thanks for your help!

Comments

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,937
    edited December 2021
    I think you will probably be alright, but we need more information. Do you have the total BTU heat loss number for the entire area to be heated?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Ironman
    Ironman Member Posts: 7,350
    What’s the btu rating of the boiler?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,322
    @Joe107

    That's like reverse engineering. The way to design a system is to do:

    1.a heat loss room by room of the building
    2.size the # of radiant loops & supply water temp and td
    3. then the water flow will be known and the circulator(s) and boiler can be picked

    But 1 1/4" pipe will transfer at least 140,000btu/hour (more for a radiant system)
  • Joe107
    Joe107 Member Posts: 23
    Thank you all for the replies. The system was sized several years ago when we built the house but before we considered finishing the basement. The heat loss for the house is 73,000 BTUs according to calculations done at that time. I calculated 11,000 BTUs for the basement and the net rating on the boiler is 103,000 BTUs. We also have a 56 gallon indirect water heater with priority zoning connected to the boiler. The house is heated using ultra-fins below the subfloor and a high limit temperature of 175 degrees.
  • With those numbers, 1¼" is fine. Frankly, 1" would work.

    .........and a high limit temperature of 175 degrees.
    This makes sense for a high limit; hopefully, your operating limit is around 120°.

    Great product, Ultra-Fin.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Joe107
    Joe107 Member Posts: 23
    Alan, Thanks for that info. Glad to hear I don't have to redo all of the piping.