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Calculating Boiler Operator Temperature.

Im reading Primary Secondary Pumping made easy and I am trying to see how I can make my Hot Water boiler better. It is a 100,000 btu Input Weil Mclain GV4. Here is where I am confused . Dan talks about subtracting the baseboard load from the equation to start.

Now I guesstimated (for now) the Length of element. Assuming 600 btu per foot at Dan says I have 80,000 btu's of element.

SO if I were to try an calculate the operator temperature I would use the equation as follows... ( if I were using the 40* delta T Dan is using.

20,000 divided by 40 X 500

so 20,000/20,000 is 1.. SO what does that mean? 1 GPM ???

Im confused now. Can someone help me understand? Thank you!


  • Gordan
    Gordan Member Posts: 891
    Keep reading

    Because now you're getting ME confused, as well. :-) I'm sure that the book explains it better than we could, so keep reading carefully until you get it. Right now, it appears that you're talking about temperature but you're really calculating the FLOW (yes, in GPM) required for water to deliver a certain BTU load with a given temperature drop. Another thing you're doing wrong is using the INPUT rating of the boiler, when you should be using the DOE output rating or the I=B=R rating depending on how conservative you want to be.
  • Pascone10
    Pascone10 Member Posts: 2
    Do you have this book

    DO you have this book? Do me a favor and start at page 80. What I am referring too is on pages 83-84. See if you can make sense of it lol.. I am trying to understand.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Start From Scratch

    Forget the board. Do a room to room heat loss. Then break it out into zones. Calcualate the flow rate required for each zone based on a 20 degree delta-t. In the real world you most likely won't even get that delta-t unless you replace the exisiting pump to a Taco VDT, Grundfoss Alpha or similar pump.

    Then measure the existing heat emitters in each room and calculate it's output at the zones flow rate.Use the attached baseboard de-rating chart to figure out what water temp you can begin a heating curve at. Take the output at the given water temp and mutiply it by your existing footage for the particular room. Do that in each and every room to find that water temp you need to overcome each rooms heat loss at design temp.By the way on a 1gpm flow rate you only get roughly 560 btu's a foot out of baseboard.

    I also attached a chart for you on how to figure your flow rate.

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