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circulator speed for constant circulation

jeffb Member Posts: 6
I have a 1 month old buderus oil fired boiler complete with the 2107 controls and an indoor room sensor. So it is running constant circulation through our single zone baseboard (fin/tube) home. The baseboard has one line out from the boiler and 3 return lines. We put a Grundfos ECM circ on it which has 3 speed settings. I've had it running medium speed (8gpm) for the past month. But now I'm wondering if I should max it out (about 11gpm) or minimize it (about 4gpm). For standard baseboard operation I know people target 20deg delta T, which it appears to be getting at medium speed on colder days (low 40s outdoor). But is that still a good rule of thumb with constant circulation? I was thinking that by raising the flow and thus lowering the delta T, it may prolong the time between firing, but it also may require the boiler to maintain higher temps to heat the house. Any thoughts on what is most efficient? Thanks in advance.


  • croydoncorgi
    croydoncorgi Member Posts: 83
    edited December 2010
    Flow versus Delta-T

    Apologies if I misunderstand, but....

    If this is a CONDENSING boiler (being oil, possibly not?) you should maximise delta-T Flow to Return to MINIMISE the temperature of the heat-exchanger.  That way, you stand the best chance of keeping the boiler incondensing mode and maximising efficiency.

    However, if it's NOT a condensing boiler, you must NOT let if condense, or it will rot out the back end of the HX!

    If you raise the flow rate, you will DECREASE the delta-T by raising the Return temperature

    Be guided by the boiler manufacturers specification.
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    edited December 2010

    put the pump on "auto-adapt". it will adjust according to the flow rates required. if you're not using the Alpha pump. try the lowest setting first, and see if the zones heat properly. increase pump speed, if required.
  • jeffb
    jeffb Member Posts: 6
    edited December 2010
    more info

    it is an alpha pump, but if I put it in auto mode it just goes at the max speed. Since it's a single zone with no valves there aren't any pressure changes for the circulator to adapt to. So I figured I should try the 3 constant speed settings.

    The boiler is not a condensing boiler, but it can take low return temps. The 2107 controls shut off the circulator when the burner fires if the return temp is
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