pump on return ??

Discussion in 'Boiler Forum' started by pool_shark_dc, Sep 21, 2010.

  1. pool_shark_dc

    pool_shark_dc New Member

    Messages:
    7
    Location:
    michigan
    got a buddy with an outdoor stove using it to heat his hot water and his baseboard heating. he's actually got an old Egor boiler. it's a waterheater and a furnace all in one. my question is on the flow side of the baseboard heating there is no pump pushing the water to/through the zone valves to the bases. there is a pump however on the return side just before it goes back into the unit... is that right or should it be on the flow side ?? he just bought the house and pretty sure it worked before but his main problem is that he cant keep the heat regulated in the rooms... he's got all the thermostats turned down but it is still hot. now with it getting hot i think it's because that pump on the return side is flowing constantly meaning that all the water is still flowing through all the pipes if i'm not mistaken. where would i hook up electric so that the pump shuts off when it is not calling for heat... hope all this makes sense... any help would be appreciated. i will try to post pics tomorrow night if i can get some if it would help.
  2. Dana

    Dana In the trades

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    Pumping toward the boiler on the return leg is good & standard practice, especially if there's much head loss in the boiler (don't know in this case what the head loss might be) . If it's pulling from the boiler it de-pressurizes the boiler, increasing the size of the micro-bubbles on the water side of the heat exchanger plates. A layer of micro-bubble foam insulates the rest of the water from the heat exchanger, reducing the efficiency of the heat exchange. If the pressure drops low enough it becomes an audible sizzle. Depressurizing the baseboard loops with the pump in it's current configuration has no efficiency consequences.

    The symptoms sound like a failure in the controls somewhere if the pump is running continously. With the pump running and all zone valves closed the boiler would be pressurized, but no water would flow. Some valves may be leaking or failed-open, but if there's no call for heat from any of the T-stats the pump shouldn't be running with most system controls. Even if the pump is off, convection loops can bring heat into zones where the zone valve has failed-open.
  3. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    Little confusing there but I think you are advocating pumping away from the boiler, toward the baseboard which is preferrable especially if the expansion tank, air eliminator and water feed valve are placed before the circulator.
  4. pool_shark_dc

    pool_shark_dc New Member

    Messages:
    7
    Location:
    michigan
    thought i might have had it all figured out because i looked at the manual for the controller and it said to connect 2 wires together then the circulating pump would only kick on with the t-stat... which is what i want... but when i went over there tonight i found out that if the circulating pump is not running then he is not able to get hot dom water. i havent taken the boiler apart but might it be that the dom water tank is surrounded by or is surrounding the baseboard water which is in turn heating each other when heat is called for ?
    keep in mind that his baseboard water is heated by the outdoor woodstove so the boiler is not on
  5. Dana

    Dana In the trades

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    Got a model number & manufacturer for the controller, and the boiler?

    Wally- I understand how the placement of the expansion tank, air scoop etc relative to the circulator is preferable, but what's the rationale for pumping away from the boiler? (It's counter to what I've been led to believe, expecially but not exclusively with low-mass high-head boilers like many mod-cons.)
  6. Dana

    Dana In the trades

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    Wally- never mind.

    If it's a low-head boiler and the system pressure is already high, pumping toward the boiler can create pressure-relive valve issues. (I'm just more used to high-head low-mass boiler primary secondary configurations...)
  7. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    OK. The point of zero pressure differential in the system is at the connection of the expansion tank and water feed valve. Putting the circulator on the feed and pumping away from the boiler allows the circulator to provide it's maximum pumping capacity relative to delta P within the system. It is very adaptable to low mass / primary secondary piping arraingements. Dan Holohan wrote an entire book on the practice (pumping away) which can be found on www.heatinghelp.com. John Seigenthaller has also written extensivly on the subject. You will find that boilers piped that way will eliminate air faster and more effectivly from the system as well as eliminate "creeping pressure" that can occur when the system pressure drops below feed pressure due to head loss in the system.
  8. pool_shark_dc

    pool_shark_dc New Member

    Messages:
    7
    Location:
    michigan
    cant find any info on the boiler but it's an Egor Duplomat. the controller is a Tradeline R8282D
  9. Dana

    Dana In the trades

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    >John Seigenthaller has also written extensivly on the subject.

    As in Seigenthaler's paper I linked to...

    The only issue Seithaler points to with pumping toward the boiler is overpressure valve sputter, as long as the location of the air scoop & expansion tank are configured appropriately.

    The sizzle issue is larger on low-mass boilers than cast iron beasts- IIRC some manufactures of the higher head mod-cons like the Contender series and some copper fin-tube boilers (pool heaters mostly) recommend pumping toward the boiler, presumably to avoid the sizzle at low system pressure (air purging issues be damned, I guess? :) ) In a primary/secondary with a low head boiler it hardly matters (according to Seigenthaler's narrative, anyway.) I'll be reading up more on this at some point- thanks for the book reference!
  10. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    nd Dana, none of any of this is new stuff. Engineers have been going back and forth with this issue for probably close to 80 years or so. One of the other changing dynnamics in play is that back then, circulator pumps were large affairs capable of moving large volumes of water through large pipes. Personally, if I buy a packaged boiler I generally leave the circ right where it comes. Expecially if I'm pulling through relatively small diameter piping loops ( 3/4 to 1" ) I have recently been using Wilo VFD's pretty much exclusively along with either a Caleffi or Taco hydronic separator. I have primary secondary piping. Huge waste of pipe and time.
    Last edited by a moderator: Sep 24, 2010
  11. pool_shark_dc

    pool_shark_dc New Member

    Messages:
    7
    Location:
    michigan
    thx for the help. it's a r8182d controller. i want the circulator to only come on with the thermostat so the manual says to connect the diff and the low limit together... now where would i be getting juice for the circulator then... ???? from the transformer?? where do i connect hot leads to ? i'm actually going to get the guy to get another heat xchanger to put on the side with his dom water for heat
  12. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    connecting the diff to the low limit, bypasses the low limit. The circ will still come on if it's wired to C2
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