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smaller boiler pump

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remodel
remodel Member Posts: 64
in THE MAIN WALL
So I had someone help me re-pipe my boiler issues, fix PONPC and a bunch of air issues and so far so good.  Static fill pressure of 20psi was enough plus high speed on the 26-99 to blow out the FCU and I am running right now.  So during design day I was running a decent  hour plus cycle even though I am 20% oversized.  Since this PIG likes to run mostly at the 20%-35% range and mostly 20% on warmer days can I reduce my boiler pump so it is designed for 50% of fire and not 100% of fire, will I have issue in the HX.  That seems to be the big problem on these manufactory recommended pumps they are designed for 100% of fire.  Manufacturer said to install a 15-58 (which was done) at speed 3.  If I do that I get a DT through the boiler of 0-3 degrees which has me up late at night with lockouts.  Right now I am running the 15-58 at speed 1.  This gives me a consistent 8.5 gpm or so through the boiler.  I am thinking I need a 4 gpm fixed speed pump with two settings, low at 4 gpm and high at 8 gpm?  Or maybe a VFD pump.  Thanks guys.       

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