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why the plumber connected the supply and return ends together

Two yrs ago, we did oil to gas conversion. In the same time, we moved the boiler from one room to another. The main line is 1" pipe. In the old layout, the ends of the return and supply was not connected. The plumber connected the ends together during the conversion. There is no other changes related to the existing pipes. There is no other device/valve attached to the individual CI baseboards. Please have the look at the diagrams attached, or big version here, <a href=""></a>. The old Oil boiler is located at top right corner and the new Gas boiler is located at the bottom left corner.

The boiler loop in the new setting is recommended by the Burnham installation manual.

My questions are what's the difference if the ends are connected and the ends are not connected? and are they both 2-pipes direct return heating system?


  • IronmanIronman Posts: 5,125Member
    Primary/Secondary Piping

    Your plumber has piped your system pri/sec as is required by the manufacturer. Your second diagram is not correct as it is showing a bypass at the boiler.

    The end of the loops should not be tied together unless you have TRV's on each rad and then there should be a pressure bypass valve at the cross over on the end. Another option would be a Delta P circ. in lieu of the pressure bypass if you have TRV's.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • Paul48Paul48 Posts: 4,492Member

    need to read more carefully.As said, the loop should not be connected.
  • heatingFunheatingFun Posts: 84Member
    second is the new setting

    The second diagram is the new setting. the bypass in the boiler is recommended by the Burnham boiler installation manual.
  • Jason_13Jason_13 Posts: 297Member
    P/S piping

    The boiler is piped somewhat correct. The installing contractor did get it pretty close but did not adhere to the distance before and after the closely spaced tee's. The returns and supplies should be tied together with the boiler tees located as is.
  • icesailoricesailor Posts: 7,265Member
    Missed something?

    Maybe I'm wrong on my understanding, but the first drawing/installation, whether primary/secondary is a direct return, with the supply and return not connected together except through the heat emitters or loops.

    The second drawing/installation is primary/secondary with a direct return (NOT REVERSE RETURN) with the supply and return connected. Effectively changing the flow through the emitter/loops unless a ball valve is installed at the end if a differential by-pass is used.

    I don't think that the installer knew what he was looking at.

    In my opinion, a valve of some type belongs in the end to keep good flow through the emitters.

    If it works, it works. If not, install a valve at the end.

    Every time I see a direst return, I think of Mark Etherton's water skiing brother in law. going in circles.

    A true reverse return may take longer and use more material but they sure do work well.
  • GordyGordy Posts: 9,264Member
    Kinda thinking along same lines

     Original piping being parallel piped where all heating loops will have same pressure drops, but different flow rates unless loops are identical so balance valves needed on each circuit.

     With the new piping as Ice pointed out. The flow rates would be less through each loop because water is lazy, and stupid like another one of ME's x brother in laws. So whats to direct a decent flow into each loop, and keep the flow from just circling the secondary circuit. Not that there would be no flow in the loops, but maybe less.  Before the flow was directed into each loop do to the pressure drop at the end of the last heating loop in the supply run.

     Maybe I'm missing something, but usually the loops coming off the secondary piping have circs,zone valves, or TRVs for each circuit.

  • archibald tuttlearchibald tuttle Posts: 632Member
    balancing act

    i tend to agree with the valve at the end plan.  the diagram doesn't really show if there were balancing valves of some sort included in the individual parallel heating loops which I assume the piping is largely undisturbed from the previous installation.

    but presumably it more or less worked the way it was.  because of the lazy water thing I would think a single valve where the mains connect would be a help.  could definitely help get larger delta T to the boiler if it is condensing style.

    Maybe the "bypass at the boiler was really diagramed as short primary loop as is common with low mass boilers and there was supposed to be close coupled tees (maybe they are) and additional circulator so that the primary secondary orginates at the boiler rather than having the mains as part of the primary loop.

    jason. which set or sets of tees were you indicating you saw as violating proper P/S distances?
  • Paul48Paul48 Posts: 4,492Member

    believe he was refering to the changes in direction on either side of the closely spaced tee's above the boiler. He may have gotten the 4x's on the return but it doesn't appear he got the 8x's on the supply.
  • archibald tuttlearchibald tuttle Posts: 632Member
    picture is worth 1000 words

    i was so busy looking at the diagrams i didn't look at the picture.

    it is hard for me to get a grip on whether the primary rounding two corners between the secondary connections means that the theoretical drop is increased between the tees more than desirable although they are close coupled. Is that the reference to not quite close enough?

    i admit to perplexity at the 4x and 8x reference.

    Sticking to the valve idea between end of secondary feed and return (or no connection as it used to be running in the opposite direction.

  • Paul48Paul48 Posts: 4,492Member

    4 or 8 times the diameter of the primary pipe.
  • heatingFunheatingFun Posts: 84Member
    more info is here

    1. There is no any control valve for each IC baseboard.

    2. The main line is 1" pipe and the size to IC baseboard is 0.5", I think.
  • Eric_32Eric_32 Posts: 264Member
    edited January 2012
    here's my .02

    Those emitters are connected to those1" main supply/return lines with regular tees, not monoflow. There is nothing that is going to make water flow in them with the mains being tied in at the end.

    While they are capped or valved "off", the flow has no choice but to go in the emitters, however I am not a big fan of this 2-pipe system. Especially when you are talking about cast iron rads. Water being lazy, will want to flow thru the easiest loops and any at the end of line will have a difficult time heating up unless valves are regulated to balance the flow thru closest emitters near the boiler.

    The return pipe, will not see any temp rise until the emitter is warm, which with large cast iron rads, can take a while. So you have to be concerned with condensing in an atmospheric boiler unless you have a bypass set up or primary/sec like in that pic.


    The OP must have some concerns or wouldn't be posting on here, is the heat output less with this new system?
  • icesailoricesailor Posts: 7,265Member
    Reverse return

    If there is a problem or a worry, I would disconnect the return at the last return tee before the boiler and cap the 1". Disconnect the by-pass connection and connect the return after the last/first loop and run the 1" back to the old return on the boiler.

    That should make that lazy butt brother in law earn his keep.

  • Eric_32Eric_32 Posts: 264Member

    what I would do. First emitter on the supply is the last one on the return. All heat even and at the same time.
  • archibald tuttlearchibald tuttle Posts: 632Member
    ok now im really confused on the 4x and 8x

    i've seen reference to multiples of the pipe diameter for spacing of tees but I don't understand how you could have different spacing for the supply and return because that is the spacing we're talking about. it would be the same for supply and return, but maybe I'm missing something.

    actually, looking at the picture again, and remembering that water takes the path of least resistance I question the wisdom of the otherwise convenient and clever use of straight through piping on the secondary loop. While the spacing of the tees is close, the corners effectively add to the spacing maybe making it too large.

    like the diagram for reversing the return and taking out the bypass albeit to clarify that is the bypass at the outer end of the loops not the bypass that is the primary loop.

    this is clearly what was suggested by the diagram but just to make the language match.

  • icesailoricesailor Posts: 7,265Member

    That 'il git 'er dun.
This discussion has been closed.


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