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3/8" PEX for panel home run system

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bmwpowere36m3
bmwpowere36m3 Member Posts: 512
in THE MAIN WALL
Hey, what are you guys using for 3/8" tubing to panel radiators of a manifold? Seems PAP is popular for its "rigidity"... however I only see it carried by ROTH (AluLaser Plus). While there are many "standard" PEX options (PEX a/b/c and PE-RT).

There are a lot more options in 1/2", however my biggest radiator has a load ~ 7000 BTUs. Given a delta T of 20-30* my flow rates in 3/8" are reasonable, while maintaining close to 2FPS. With 1/2" I think I would be over-pumping to maintain at least 2FPS.

Locally I know for sure I can get ROTH and Uponor tubing.

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  • Gordy
    Gordy Member Posts: 9,546
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    Larger dia. tubing has little consequence other than workability, and cost. Another thought is your radiant floor. sandwich or underfloor?

    running in the 4-5 FPS range is not a problem.
  • Snowmelt
    Snowmelt Member Posts: 1,415
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    Yum sorry to say or ask I'm confused by the question, are you asking what pex brand I use?
  • SWEI
    SWEI Member Posts: 7,356
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    3/8" PEX-a routed through the walls. Transition to 1/2" copper if routed through the floors.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    I would use 1/2" for the fact that it's a more common size and fittings are readily available.
  • Snowmelt
    Snowmelt Member Posts: 1,415
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    Ditto bob
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    Gordy said:

    Larger dia. tubing has little consequence other than workability, and cost. Another thought is your radiant floor. sandwich or underfloor?

    running in the 4-5 FPS range is not a problem.

    Radiant floor in bathroom will be dry sandwich. Future addition will be in slab.
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    Snowmelt said:

    Yum sorry to say or ask I'm confused by the question, are you asking what pex brand I use?

    Sure, what do you guys like to use for sizing and brand/type. There are a lot of options from different manufacturers, PEX-a, PEX-b, PEX-c, PE-RT, PEX-AL-PEX, PERT-AL-PERT....
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    SWEI said:

    3/8" PEX-a routed through the walls. Transition to 1/2" copper if routed through the floors.

    They'll be routed in/under floor joists (basement), then thru floor to panels (Buderus, bottom connection).
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    With 1/2" tubing, my rough calculations indicate that to keep flow velocities at 2+ FPS the required GPM would result in delta Ts ~12* (design day) and would only get smaller as temps go up.

    Maybe doesn't really matter... 1/2" is a lot easier to find fittings for.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    Big fan of Viega Fostapex. Readily available fittings, tools don't cost an arm and a leg. When Uponor (then Wirsbo) came out with MultiCor, 15 years or so ago, I was pumped (pun intended) but back then fittings were limited, and the crimp system was very new. And obscenely expensive. Looked at Kitec briefly but they vaporized. Then Fostapex came to market. Sold.
  • Gordy
    Gordy Member Posts: 9,546
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    Agree with Bob.

    DONT get wrapped up in deltas its rampid around here. Design with them. Narrower delta just means a more average temp across the rad. Pump energy is saved with larger diameter tubing. The TRVs will take care of the deltas. Your piping P/S Boiler delta will be more significant.
    Bob Bona_4Harvey Ramer
  • SWEI
    SWEI Member Posts: 7,356
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    bmwpowere36m3 said:

    They'll be routed in/under floor joists (basement), then thru floor to panels (Buderus, bottom connection).

    The bottom connections work great with either 1/2" or 3/8" PEX. No worries about sagging like the top end pipe does.
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    SWEI said:

    bmwpowere36m3 said:

    They'll be routed in/under floor joists (basement), then thru floor to panels (Buderus, bottom connection).

    The bottom connections work great with either 1/2" or 3/8" PEX. No worries about sagging like the top end pipe does.
    Would you still recommend coming thru the floor with copper pipe? It would be about 4-6" exposed. Or just run PEX up to the radiator and install the plastic covers that come with the panels?
  • Snowmelt
    Snowmelt Member Posts: 1,415
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    3/4 manifold viega if your running pex to each room might as well run a thermostate. With a bumble bee pump.
  • hot_rod
    hot_rod Member Posts: 22,158
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    Panel rads cry out for TRVs and delta P circs :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,546
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    Ditto,HR is there really a better way?
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
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    hot rod said:

    Panel rads cry out for TRVs and delta P circs :)

    That's the plan…
  • SWEI
    SWEI Member Posts: 7,356
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    bmwpowere36m3 said:

    SWEI said:

    The bottom connections work great with either 1/2" or 3/8" PEX. No worries about sagging like the top end pipe does.

    Would you still recommend coming thru the floor with copper pipe? It would be about 4-6" exposed. Or just run PEX up to the radiator and install the plastic covers that come with the panels?
    The latter, if I were doing it.
    bmwpowere36m3

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