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  1. #1
    Join Date
    Mar 2013
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    Need advice on using Taco Bumblebee pump on new boiler installatio


    I am thinking of using a Taco Bumblebee pump on the primary (boiler) side of a new Alpine installation.

    It seems that it wiould allow me to set the high Delta/T on the boiler I want and maintain it throughout changes in modulation and changes in the secondary.

    What concerns me is keeping adequate flow through the primary at all times. As the D/T lowers the pump GPM should lower and perhaps get to a point where there is not adequate flow to scrub off the heat on the HX. Does anyone have experience with these pumps? Can I program a mim flow rate to not go below?

    Thanks for any advice,


  2. #2
    Join Date
    Jan 2009
    Saint Joseph, MI
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    Most boilers want a fixed flow rate on the primary. But using a fixed delta T could give you lower return water temps, if you control your outdoor reset based on return water temps, not supply. But you'd need to maintain a minimum flow rate unless you limit return water temp. Rather than delta T, you might try and maintain a fixed return water temp.

    the pump should have a minimum flow, but I'm not sure if you can set that minimum range. You might download the manual and look it up.

    Ideally your using a good boiler pro for this, and he can answer all these questions. Water flow is everything on a boiler and a mod-con in particular needs low return water temps for effceincy. What the industry doesn't tell you is that Mod cons are really best suited for low temp heating like radaiant floor and radiant panels, not hydro air or fin tube. They can work with cast iron and steel radiators if you have enough EDR.

    SOme Combi boiler for example, will need a 30, 40 or even 60-70F delta T to hit max fire rate. With radiant floor or mixed temp zones on a P/S, that's possible in mid winter.

  3. #3
    Join Date
    Jul 2000
    Northern Wisconsin
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    I personally wouldn't use a VDT pump on the primary side of a low mass mod-con boiler. Your thinking of maintaining a set delta T across the boiler is ok if it's a cast iron or other larger mass unit, but when it comes to the low mass high input capable units different things come into play. There is no real advantage to using one on the primary loop of a HE mod-con. IMO

    Case in point would be if a cold zone opened up and the boiler's sensor ramps up the burner to maintain set point of delivered water. How quickly the burner ramps up verses how fast the VDT pump can react to the added btu's being put into the primary loop better be a perfect match or one of two things are going to happen inside the heat exchanger/boiler ...... the burner is going to ramp back down or you run the risk of causing hot spots in the heat exchanger or worse flashing some of the liquid to steam.

    Use the VDT type pumps where they were designed for.... delivering the exact amount of btu's to the zone load.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

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