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Direct Return Pump Question

NYplumberNYplumber Member Posts: 472
Good evening. Pondering some would be circumstances on a job I looked at. From the look of the piping it looks to be direct return. Boiler like most is over sized. Piping over sized. Radiators much larger than needed. Assuming it is a direct return system at this point. With three zones, each for its own floor, cast iron wall radiators all around the home. Calculating the DT and reverse doing the math to plot it on the current pump, I see that the Bumble Bee will fit the bill. Staying away from calculating using worst case scenario length x .06 because the pump will be grossly over sized in comparison to what is there and has been working for 15 years.

My question is, when the pump slows down to widen the dt, will the water short circuit through the closest radiators due to the lack of constant head pressure? Adding trvs under each radiator is out of the question.

Ideas and advise welcome.


  • gennadygennady Member Posts: 664
    edited May 2013
    Pump slow down

    Pumps slow down will lead to increased effect of gravity circulation. So top floor radiators will get the most of the flow. Make sure top floor radiators have working valves.
    Gennady Tsakh

    Absolute Mechanical Co. Inc.
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,380
    Heat loss calculation

    Will the new boiler be sized to the heat loss?--NBC
  • NYplumberNYplumber Member Posts: 472

    Im am not concerned about the upper floors as the thermostat will close upon heat need being satisfied. The boiler output temp will be sized close to the needed temp to run continously so less of a problem.

    Thinking of trying the new Cadet boiler by lochinvar.

    As for zone valves, other than White Rodgers, who makes 1 1/4 inch or larger valves with a high CV (low pressure drop)? Tavo has high cv valves only in 1 inch and below.

    And a heat loss will be performed.
  • Paul48Paul48 Member Posts: 4,059

    It will short circuit. And balancing becomes a challenge, a near-impossible challenge with an ever changing zoned system.
This discussion has been closed.


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