Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

WM indirect water heater boiler side piping

Looking over the installation manual I noticed that the recommended boiler side piping for the Weil Mclain Gold Plus indirect water heaters seems different than what I'm used to seeing. So I dug up a bunch of manuals for other brands, and they are all opposite of the Weil Mclain. WM says the boiler water goes in the bottom and out the top (parallel flow), others are saying in the top and out the bottom (counter flow). Can anyone explain why they are doing it different than all the others? I've done some research on parallel vs counter flow in heat exchangers and found the following:

"The design of a parallel flow heat exchanger

is advantageous when two fluids are required to be brought

to nearly the same temperature. 

The counter-flow

heat exchanger has three significant advantages over the

parallel flow design. First,

the more uniform temperature difference between the two

fluids minimizes the thermal stresses

throughout the exchanger. Second, the outlet temperature of

the cold fluid can approach the

highest temperature of the hot fluid (the inlet temperature).

Third, the more uniform temperature

difference produces a more uniform rate of heat transfer

throughout the heat exchanger."


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    W-M Indirects are like Triangle Tube Indirects.

    I have a W-M 36 gallon (or so) indirect and as you say, hot supply goes in the bottom and the return comes from the top. So I looked at Triangle Tube's installation manual for their indirects for an explanation, and it is worse with those. It appears that the the SMART series and the  smaller ones of the TR series are done the same as the W-M ones. But for the larger ones  of the TR series the hot goes in the top and the return comes out the bottom. So, as the King of SIam said, it is a puzzlement.

    My theory, and it is only a guess, is that they want the water at the bottom of the tank to be as hot as possible, so they put the boiler water in there. They might want this to kill off any bacteria growing at the bottom. The price is that the hottest the water you can get out of the tank, if you are in a hurry, will be somewhat less than the boiler supply water. It may run slightly less efficiently than plumbing it the other way around, if you  consider a hot water to be only a heat exchanger. But as I said, this is only a guess.

    I wonder who actually makes these things. My W-M says Made in Belgium on it. I never saw a TT one. Does TT have their factory in Belgium? Or do they both by their units from the same manufacturer?
  • Interceptor
    Interceptor Member Posts: 46
    Tank in Tank

    I thought it may have something to do with the WM being a tank in tank as opposed to coil in tank, but then I saw a Triangle Tube tank in tank piped the other way. I'm guessing it doesn't really matter which way it's piped, maybe a

    small percentage of efficiency or performance gained or lost either way.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    tank within tank

    I just looked TT indirects up when I made my earlier post, and they are to be piped the same as the W-M ones. At least their Smart series are. It is my brief experience that installers do not read the installation manuals. Mine filled the outer tank before they filled the inner tank, for example, even though I pointed out that W-M insist the inner tank be filled first. They said they always did it that way. Well, perhaps they did, but that did not make it right.

    ANd they were about to pipe the hot into the top and return from the bottom until I pointed out the to the foreman the chapter and verse from the installation, so he did it right. But he would not have. I bet some contractors hate to have me around when they are working.

    I know why W-M want the inner tank filled first. I do not know why they want the boiler water to enter at the bottem, and my earlier guess I will continue to believe until someone with the facts confirms or corrects me.

    It makes me wonder why manufacturers bother ot go to the trouble and expense of making installation manuals when technicians are proud of the fact that they do not read them I suppose a higher propertion of people here read the manuals; at least I would like to think so.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Same here.

    I piped my Smart 60 per the manual, supply in bottom.  The tappings are even marked that way, so I find it odd an installer would do it opposite.  I always read the manual, even if it's on a product I already installed, just to make sure something didn't change.  I never mind someone watching me work, because I'll put them to work :) (free helper). But unfortunately, I don't know your answer either.  I hope a manufacturer's rep can chime in.

    There was an error rendering this rich post.

  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Weil is TT

    Same tank different jacket.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
This discussion has been closed.