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Rinnai E50C air scoop and expansion tank

eddo Member Posts: 12
One last (I hope) question about my E50c. The install manual shows the air scoop and expansion tank on the return side, close to the low loss header. A Rinnai system piping manual for the same E50C has the air scoop where I've slways seen them, on the supply side right before the circ pump, but with the expansion tank on the return side. I've asked Rinnai tech support if there's a specific reason why either of their illustrations show it set up like that, if I should do one or the other, and why they're different from each other. So far no answer; it got escalated up the chain to the engineers, but no word back yet. Any thoughts? Without their illustrations I would have mounted the tank below the air scoop on the supply side right before the pump.


  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 3,936
    edited October 2018
    I would pipe it as in your last sentence, pumping away from the expansion tank.

    BTW, that's a great combi boiler. Why didn't you get the Rinnai low-loss header?
    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
  • eddo
    eddo Member Posts: 12
    Thanks. Yep, I just talked to Rinnai engineering. I went up the ladder through 3 tech support guys until they gave me right to engineering. The illustrations are wrong! Can't believe I'm the only one who caught that, it's been out for years. Best practice is what I assumed, air scoop and expansion tank on the supply side before the circ pump. The guy did say, though, that it wouldn't be really bad to do it the other way, just not best practice.
  • Tom_133
    Tom_133 Member Posts: 880
    edited October 2018
    Im not sure what pic you speak of but the only one I can see in the manual, shows air scoop on the supply, and the expansion tank and fill valve on the return side. That is the correct way to pipe it if your system requirements allow you to use the internal pump as your system and boiler pump. Air scoop should ( when possible ) go on the hottest water temp side, and the expansion should be on the return to keep the PONPC on the side that would already have the lowest PSI due to the friction loss of the heating circuit. If you are piping primary secondary, that would change everything, and I didn't see that pic in the manual.

    Montpelier Vt