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hw heating- pumping through boiler?

steamfittersteamfitter Posts: 62Member
After reading both "Pumping Away" and "Classic Hydronics" I have learned a lot about why hw circulators should be on the supply pumping away from the boiler for optimum performance of a hw heating system.

While surfing through Weil-McLain's website, I came across the manufacturer's recommended piping of some of their boilers suggesting to pipe the circulator on top of the boiler. However the flow showed the circulator pumping into the boiler even though the diaphram comp. tank and water feeder was near the circulator on top of the boiler. The PONPC was on the suction side of the circulator as it pumped through the boiler making the lower connection the supply instead of the return.

Now I'm a little confused???

Can anyone explained this to me? I'm sure it works but is it the best way? Weil McLain must know, no?


  • hot rodhot rod Posts: 4,486Member ✭✭✭✭
    pumping into

    the boiler is often suggested on many of the newer mod-con boilers. The restrictive heat exchangers benefit from the additional pressure the circ provides. You can still locate the expansion tank on the inlet side of the pump and "pump away". The air eliminator could be on the supply side, the tank connected at the pump instead of the air purger.

    Primary secondary and hydro separators are another challenge for locating the expansion tank connection.

    Here is a link to an excellent article from PM magazine the Siggy wrote awhile back.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • IronmanIronman Posts: 2,361Member ✭✭✭✭
    Not Exactly Following Your Description...

    But the PONPC should be on the suction side of the circ. It is the PONPC that the circ. should be "pumping away" from, not necessarily the boiler. If the boiler is piped off of the primary loop using two closely spaced Tee's, the the boiler's circ. should pump into the boiler, not draw out of it.

    When you have p/s piping with the expansion tank being in the primary loop, every secondary loop "sees" the entire primary as the PONPC.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • IronmanIronman Posts: 2,361Member ✭✭✭✭
    Thanks, Hot Rod

    I was looking for Siggy's article in my documents and couldn't find it.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
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