Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Boiler piping configurations

t_6t_6 Member Posts: 6
I'm in the final stages of renovating an old multi-unit rowhouse, which includes all new heating systems using Burnham Alpine condensing boilers (one for the ground floor unit, and a second for the upper floors). 

Without getting into too much background, it only recently came out that the GC & plumber have never before installed condensing boilers. 

I'm now questioning whether the systems have been correctly piped, as the piping does not seem to be as per the Burnham I/O manual.  In particular, I'm unsure about the lack of distinct boiler and system loops, and the use of the mixing valve for the radiant slab (instead of just lowering the boiler setpoint), and the water heater return connected prior to the boiler/system circulator.

I've attached diagrams for the two systems -- can anyone advise if there are glaring problems, issues that may cause poor performance, equipment failure, etc?


  • LarryCLarryC Member Posts: 331
    edited January 2011
    Why are you bypassing the emitters?



    In both of your diagrams, you show that you are short circuiting the emitters, by directly connecting the supply to the return.  Is that  the actual plumbing or a drawing mistake?

  • GordanGordan Member Posts: 891
    Are you leaving things out of the diagrams?

    For instance, the first diagram seems like it shouldn't work unless there is a differential pressure bypass valve on the leg connecting the supplies with the returns. The reason is the "short-circuiting" that Larry mentioned.

    For the second diagram, the mixing valve would be restricting (and potentially blocking) the flow in the "boiler loop" - that's not how a mixing valve should be piped. At least there is no "short circuiting" there, but neither is there proper hydraulic separation between the boiler circulator and the zone circulators. The mixing valve itself may be nothing more than a "high limit" intended to prevent hot water from hitting the slabs after a DHW call (or due to a malfunction) and not the primary means of supply temperature control.

    There are other issues with the depicted diagrams, such as missing check valves on the zone and indirect circuits, pumping toward the expansion tank, and the weird way the DHW circulator pumps through the boiler circ.
  • John Mills_5John Mills_5 Member Posts: 935
    Something fishy

    Been a couple months since my Alpine class but seems like you are missing a pump! Seems to me there needs to be 3 pumps. I'd put the tank in the piping for the radiation and pump away from the tank to the radiation. Then a boiler pump and a pump for the water heater.

    Somebody needs to see Figure 32 Page 47 of the Alpine manual!
  • t_6t_6 Member Posts: 6
    edited January 2011

    This is as installed.  My understanding from the Burnham manual is that a loop is required (the manual states "direct connection of boiler to heating system, similar to a conventional boiler, is not recommended because the flow rate through the system must be the same as through boiler and fall within the limits specified...")

    That said, the manufacturer's diagrams do not show a bypass quite like this, and the manual states "Near boiler piping must isolate boiler from system piping via closely spaced tees to insure specified flow range through boiler ... flow rate through the isolated near-boiler loop is completely independent of the flow rate through the heating system loops"
  • t_6t_6 Member Posts: 6

    There are no valves on the bypass piping for either boiler.

    I asked the plumber about this (why does water circulate through radiators when there's a bypass) but he couldn't really give an explanation.  The radiators do get hot, but very slowly; I suppose they're functioning somewhat like in a gravity system?

    In the second diagram, the mixing valve was to get the 180F water to 140F for the radiant slab (something I questioned, as the boiler setpoint could be adjusted down, though I don't know if that causes issues for the DHW).  The "bypass" was just added because the boiler was hard-faulting from inadequate flow when only one zone was on.  (The issue that lead me to question the entire system configuration)

    I did leave a few things out (automatic fill valve at expansion tank, and probably some other valves -- I'm an architect, not a plumber.  The diagrams are just based on field observation).
  • t_6t_6 Member Posts: 6

    The Burnham manual does show three pumps, in conjuction with separate boiler and heating loops.  The manual also shows the expansion tank connected to the system piping, and not the boiler loop.  I questioned the placement and was told that they could not connect it there due to room layout.  Is the tank location a problem?
  • GordanGordan Member Posts: 891
    That sounds about right

    I'm not surprised that the second boiler is hard-faulting - as I pointed out, the mixing valve would throttle off the flow through the boiler anytime that it needs to mix in a sizable portion of the return flow.

    I'm not familiar with the Alpine but typically these boilers have the ability to set the supply temps independently for DHW calls and space heating calls; I'd be shocked if the Alpine didn't. You'd also benefit from outdoor reset, especially on a high-mass system. Heating the water to 180F only to mix it down to a lower temp defeats the purpose of a condensing boiler.
  • GordanGordan Member Posts: 891
    Room layout?

    That's a pretty ridiculous excuse. An expansion tank can be physically almost anywhere, but its connection to the system needs to be at the correct location relative to the other system components. Has this plumber not heard of pipe?

    What's his excuse for not piping the boiler primary-secondary, using closely spaced tees? Did he run out of tees?

    The tank location can be an issue, yes. It can cause circulator cavitation and other issues. But that's not really the point. You should not have to justify why a contractor whom you pay to install your heating system should install it according to the manufacturer's instructions. There are much bigger issues with the installs than the tank location, as already laid out.
  • t_6t_6 Member Posts: 6

    Thanks; we do have outdoor reset wired but not enabled.

    I'll have to digest the installation manual a little more and have a talk w/ the GC.
  • Mark EathertonMark Eatherton Member Posts: 5,843
    Tell your plumber to R.T.F.I.M.....

    That is computer geekism for Read The Freaking Installation Manual!!!

    Their piping is NO WHERE near being correct.

    This system has to be piped primary secondary.

    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.
  • Tombig_8Tombig_8 Member Posts: 15
    Yeah...What He Said!!

    Follow the I&O piping diagram. How the frik did they even wire the pumps?? There's terminals for boiler, system, AND DHW pumps. What a mess. Use the OD reset on both systems, especially the first floor if it's CI radiators. You don't need the mixing valve at all if all the 2nd floor radiation is single temp radiant floor. The floor circulating temp can be set at the boiler and the boiler will ramp up on a call for DHW. Make sure there are check valves on the 2nd floor zone pumps. Back to the drawing board for this installation for sure. Sorry to be so negative but this is waayy wrong if piped as drawn. Your plumber needs to bring in a boiler professional to adequately extricate himself from this mess. Best of luck.  
  • Jean-David BeyerJean-David Beyer Member Posts: 2,663
    RTFM: Absolutely.

    I felt like commenting on this before, but I was too disgusted, and also I knew others would feel the same.

    Right on the front cover of the manual you provided, it says:

    WARNING: Improper installation, adjustment, alteration, service or maintenance can cause property damage, injury, or loss of life. For assistance or additional information, consult a qualified installer, service agency or the gas supplier. This boiler requires a special venting system. Read these instructions carefully before installing.

    Then on page 47 it gives a diagram on how to do it. Why did the installer not do it? Functionally illiterate? In another thread, I said about the manufacturer of my boiler, I wish W-M would not sell Ultra boilers to companies that do not know

    how they work, how to install them, and how to maintain them.
    I guess that applies to all boilers.
  • GordanGordan Member Posts: 891
    Let's not forget combustion and venting

    If the plumber got the piping part of the job this wrong, I'd be very concerned about the venting, not to mention combustion settings. And there, you could REALLY create issues that negatively affect the longevity of the boiler... or the inhabitants.
  • clammyclammy Member Posts: 2,496
    Common as usual

    This is  some thing i myself hear as  explained to me  by those who don't pipe either  mod cons and steam boilers correctly " who has time to read " and then directly after wards comes "i don't have the money in to do that ! " this all also seems to always have a GC some where in the picture .Aside from that rant nobody seems to be able to read nor understand simple P?S? piping  ,if piped as drawn it ain't right by a long short and if that is so i would also wonder about the rest of the install and the concept they used to piece it together .Mod Cons benefit from lower water temp operation hope they designed the hi temp side for low water temp.Make them re-pipe and use the domestic hot water sensor for that tank  with a separate pump for it and use some Primary secondary piping techniques and read the DAMN instructions peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • CMadatMeCMadatMe Member Posts: 3,066
    edited January 2011
    Instead of Re-Piping

    Primary/Secondary maybe easier to install a low loss header. Tell the guy to open the manual like the rest have posted. System will not work if it truly is piped as your diagram shows.

    Boiler 2 with the radiant doesn't need a mixing valve. The condensing boiler is your mixing valve!
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!