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There is a new note on HTP Elite Piping instructions.

OldSkool Member Posts: 18
This summer I am going to finally fix the boiler piping on our home here.  As I read the HTP Elite piping instructions/suggestions I see a new note (among others) that I have not seen in any of my pre-work for this project.  The note starts as follows:

 <strong>  5.</strong>  <strong> System flow (secondary loop) should be greater than the boiler primary loop flow.</strong>  

My installation here is actually a Munchkin 140M, and the Vision 1 drawings do not have such a note, but just trying to learn, does anybody have any idea what in the heck are they talking about?   Proper primary/secondary hydraulic separation should make the various loops in a system unaware of flow differences, right?  Am I perhaps missing something?   Page 23 of the attached HTP Manual is included for context.



  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    System flow (secondary loop) should be greater than the boiler primary loop flow.

    My Weil-Maclian Ultra 3 installation instructions say no such thing. But that is a different boiler and a different manufacturer from yours.

    I could imagine it makes sense.

    Let us say that for some unexplained reason, the boiler (in the primary loop) fires up and for some reason, the circulator(s) in the secondary loop do not run. The flow in the primary loop will not notice the absence of flow in the secondary loop because of pressure changes. But the heat produced by the boiler will have nowhere to go, so the primary loop temperature will go up very fast.

    Now the controller in my boiler will notice the temperature going up too fast, and will lock out. It might be a low water condition (not in this case, but it does not know), or the flow in the secondary loop may be too low, etc.

    But perhaps your boiler controller cannot shut off the fire fast enough, and they want protection from that.

    In my system, the boiler circulator is a Taco 007. The secondary is two zones, each controlled by a Taco 007-IFC. If the resistance of all the loops is the same, and both secondary loops are calling for heat at the same temperature, the flow in the secondary loop would be double that in the boiler loop. But those loops, it is safe to say, are all different, with the boiler loop likely having the lowest resistance of all. And usually, only one secondary loop runs at a time. So with the previous assumptions (false), the secondary loop would then run at flow rate equal to the primary. In practice, I am quite sure that one of those zones has quite a bit more resistance than the boiler loop, so I do not meet those requirements.
  • SWEI
    SWEI Member Posts: 7,356

    Isn't this just another way of saying that ∆T in the secondary loop is lower than in the primary?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    Thats pretty funny...

    Because in a multi zone system, that will only happen at design condition, which is less than 2% of the time.

    In my minds eye, other than confusing someones hand in an Oohh Aahh test (using your hands to feel the pipes temperatures) the control doesn't care, and will see the demand based on the true boiler delta T, and not the systems delta T.

    If you want to know for sure, contact Mr French at HTP's engineering department for clarification.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • OldSkool
    OldSkool Member Posts: 18

    Thanks you guys for the considered responses.  I did try calling HTP technical support about this and was told since I was working on a Munchkin, not an Elite boiler I should use the Munchkin piping suggestion (there is no note about secondary flow rate on the Munchkin drawings).  I was surprised at that answer; I suspect they were quite busy at the time and just didn't want look at what I was talking about.

    I do note that the coment says "should" and not "must", but I  am still left wondering what HTP knows about closely spaced tees that I don't.

    Again, thanks to all that commented.  I'll post here if I ever find out what was intended by the note. 
This discussion has been closed.