Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Microbore-style Systems in the US?

NTL1991 Member Posts: 103
Hey guys. Came across some pictures of microbore systems over in Europe and I’m impressed with the 8-12mm pipes they use to connect their panel rads. Anyone know of any systems like this here in the US? I’d be curious to know how the heck they can get sufficient BTUs through pipe that small. Also curious about what kinds of static pressure and pumps they’d be using.

Sure looks like it’d be easy to fish that pipe anywhere you needed it.
Nick, Cranston, RI


  • Big Ed_4
    Big Ed_4 Member Posts: 1,775
    I always run 3/8" on my home run systems .but use "A" Pex ... 1/2" can deliver 28K why use if the radiator is much smaller .. The problem is finding 3/8" manifolds .. They disappeared .... Do you think 1/2" is easy to run , try 3/8"

    In the early fifties spaghetti systems where installed , home run system using convectors . They even used tube type outdoor resets behind the kitchen clock ....

    Over there they ask for the best , over here we ask how much ...

    I have enough experience to know , that I dont know it all
  • hot_rod
    hot_rod Member Posts: 15,019
    edited September 2020
    Euro based systems often run wide deltas, 30 to sometimes 40 delta 
    The also do home run piping so you don’t take that series radiator piping temperature drops
    So short, small diameter tube running high deltas

    Caleffi offers 3/8 Pex fittings for manifolds, a nice universal fitting for all types and brands of Pex 
    As well as the 5/16 diameter fitting.

    Properly designed that 5/16 Uponor  or Viega could be used fo radiators if you want small readily available US (micro) Pex.

    Here is the Viega pressure drop chart.
     Consider a 1 gpm flow in a 100' loop, of 5/16" pex, running a 30 delta, which would be 15,000BTU/ hr
    500 (f) ∆T
    500 X 1X 30∆= 15,000
    100' loop X.002/ft. = 2 psi pressure drop
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 15,019
    Caleffi Pex fittings for manifolds, TRVs etc.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream