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Replacing wet returns, resize or not?

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JimVT
JimVT Member Posts: 21
First some background on my project. I'm replacing a circa 1940s American-Standard Oakmont model 1BJ3 that was fired at 1.5 GPH with a MegaSteam boiler and ran into a disagreement with the supplier rep. He said my only choice was the MST629 because he was concerned about condensate return time. I thought the total EDR of 500 meant he was oversizing so the MST513 was the best choice and it fired at 1.35 GPH rather than his choice of 1.65 GPH. I suggested modifying the Burnham dropped header piping kit to accept an equalized reservoir tank and to install one only should we have this problem but he doesn't believe in these tanks. I gave up on this discussion with him and pondered the problem at home. From the installation and operation manual I knew the total water capacity of each of the boilers when a tankless coil is installed so I calculated how long each model could steam if it used up all the available water (not that the LWCO would allow this) and found that the largest three models would each steam for the same length of time and the smallest one would steam the longest! I've decided that I don't trust the supplier rep and told my heating contractor to proceed with the MST513 installation and to modify the piping kit by adding two tees each with a plug.

As far as I know the wet returns are the ones originally installed with the boiler so they will be replaced. My question is why not resize one of the wet returns to increase the water available for steam production? The longest wet return is about 44 feet of 1" pipe and much of that would be near the normal water line. Increasing this pipe to 1.25" would add almost 1.5 gallons and increasing it to 1.5" would add about 2.7 gallons. The shortest pipe is about 23 feet long but it is 11" below the other so it would add very little water near the water line unlike an equalized reservoir tank. Would these changes cause other problems since the Burnham piping kit equalizer is only a 1.5" pipe or might it adversely affect the condensate return time? Should the long wet return be replaced with the same size pipe, increased to 1.25" or 1.5"?

Comments

  • JUGHNE
    JUGHNE Member Posts: 11,061
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    This was discussed recently. More water in the wet return pipes will not give you more water in the boiler. The wet returns stay full of water. No matter the size if you add 1 gallon into the return end only 1 gallon will come out to the boiler end. IMO

    Provisions for the reservoir tank seem to be the logical solution.
    It needs a steam connection on the top and return connection on the bottom. It needs to be raised up to the boiler water level.
    Think of it just like a buddy boiler but with no fire under it.
    I would also add provisions for cleaning it out just like a boiler.
  • Jamie Hall
    Jamie Hall Member Posts: 23,295
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    This ^^^. To which may I add -- have you sized your new boiler accurately to the EDR load of the structure? Please do...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,526
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    As @Jughne mentioned over sizing the returns wont help.

    The only water you have to work with is from half a gage glass to about 1/2" above the bottom of the gage glass.

    I would pipe the boiler normally leaving a tee in the supply header and one in the return so a tank can be added if need be.

    Make sure any wet returns you pipe are below the bottom of the new boilers gage glass.

    I would make any wet return at least 1 1/4"
  • JimVT
    JimVT Member Posts: 21
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    Wow, what you're telling me is that my wet return has always been piped wrong! I've attached some pictures of both returns on their way to the pit where the old boiler sat.


    Main 1 and wet return 1 with NWL white label at elbow


    Wet return 2 with NWL white label & mason twine, main 1 and wet return 1 in background


    Wet return 1 above and wet return 2 below with NWL white label & mason twine


    Wet return 1 with NWL white label & mason twine


    Wet return 1 above and wet return 2 below, another view


    The pit with NWL label highlighted

    Unlike wet return 2 which quickly dropped to floor level and almost burrowed in the dirt on the way to the pit, wet return 1 didn't follow the rules but I'm not aware that it ever caused any problems. As you can see it does have quite a lot of it's 44 feet very near the normal water line and in fact 30 feet are within three inches.
  • dopey27177
    dopey27177 Member Posts: 887
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    Your wet return was sized correctly.

    Wet returns are sized smaller than dry returns because they do not have to carry steam, condensate and air.

    Dry returns were installed where a wet return could not be installed due to a buildings configuration or the contractor did not want to install the black steel return pipe underground.

    if you decide to use the wet return install a clean out Full Size at both sides of the wet return. If you will install underground I suggest you use type K copper and silver braze the joints.

    This will be a return that will never have to be replaced.

    Jacob Myron

  • JimVT
    JimVT Member Posts: 21
    edited October 2019
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    Thank you all for your comments.

    I wonder now when return 2 is re-piped if it should also be done with 1" pipe since the EDR on Main 2 is less than 700. The vertical pipe there is the system A dimension of 36.75" and wouldn't reducing at least some of it to 1" pipe improve the condensate return since it would stack up quicker? How much of the vertical pipe should stay at 1.25" below the reducing elbow at the end of the 2" main or should the reducing elbow be changed to continue the 2" pipe for a few inches down before reducing it to 1"?
  • clammy
    clammy Member Posts: 3,111
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    On sizing wet return I usually try to go over what is rated it gives you a little leeway for mud ,rust and sediment to build .i believe this is why most wet return where original slightly oversized to allow for crap to build up .now a days most size them at the smallest pipe so there the most difficult to unclog .when redoing wet return s I like to add isolation valves and tee s so I can pressure test over time looking for leaks and to have the ability to power flush crap out every few years before it’s totally plugged .Dry return are a different story Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • clammy
    clammy Member Posts: 3,111
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    Ps larger return lines do not give your system more steaming water volume only a reservoir tanks hung at the mid point of the tank in realationship to the boilers water line will do that again Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • JimVT
    JimVT Member Posts: 21
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    Thanks @clammy. I was planning to add the tees and valves for clean out of the returns but wanted to ask if an isolation valve should also be added above the tee near the end of each main? So I'd have at the end of my two mains a full ball valve above the tee with a boiler drain valve to accept a hose connection as well as the full ball valve to isolate the Hartford loop down in the pit and the other full ball valve at the tee to drain into my sump pump.
  • clammy
    clammy Member Posts: 3,111
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    That’s the way I prefer to do them it a sure key to ease later in the systems life and for preventive maintenance every few years Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating