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Proper height of return for 1 pipe steam system

Just a forward - I am not a plumber, just a homeowner that likes to tinker - and if I have it - I like to know how it works in case I need to fix it. That being said....

My neighbor called me last night because his steam boiler was not working. It turns out he has a bad leak on the return, the boiler emptied out and the low cut off switch shut off the boiler.

The system is a single pipe - gas fed - steam boiler, the boiler was replaced in 2012, but hooked up to all the old piping. The old return ran along the floor into the boiler for the old boiler, however the new boiler has the return coming into the boiler about 12" up off the floor. The person who did the install ran piping down to the return to connect to the old return - with a valve in the middle (I guess for servicing)

My question is - does it make sense for the return to be lower then the boiler and not gravity fed ? Isnt there always going to be water sitting in that line that is below the connection to the boiler. On my Steam boiler (before we switched to hot water) - the return line had a slight pitch directly into the boiler. The way my neighbors is piped - it seems like there will always be water in the return line below the boiler - which cools down and causes the boiler to work harder heating up this extra water. I understand the system can work like a P-trap on a plumbing line and as more water condenses it will push the water in that pipe into the boiler by gravity but isnt this very inefficient because all that water has cooled down ?

He always complained of astronomical heating bills but thats also due to bad windows, poor placement of thermostat, etc. I am wondering if the boiler is overworking to reheat the water that is sitting at the bottom of the return.

See below for sketch of the basic layout of his boiler.



  • KC_Jones
    KC_Jones Member Posts: 5,749
    Any return below the water line does not need gravity to work. Water seeks it's own common level, so a drop coming in at one ends pushes a drop out the other end.

    That said a little slope to help flush those wet returns never hurts.

    There is nothing wrong with a wet return. All boilers have some amount of them as you should have a trap into the hartford loop, and for any of the regulars I am not stating that to start up the hartford loop discussion.

    The amount of cooling going on in that wet return isn't contributing much to the high fuel costs. There isn't a tremendous volume there. My wet returns are only a couple feet and that little bit, on most days, will get to ambient temps before going into the boiler.

    Pictures of the install would help, but without seeing anything I would guess it has messed up near boiler piping and over sized.

    If you want an honest assessment post some pictures of the boiler and associated piping.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • dopey27177
    dopey27177 Member Posts: 887
    Sketch taken from my book steam the perfect fluid for heating and some of the problems

    EBEBRATT-Ed Member Posts: 15,829

    What @KC_Jones said is correct. Below the water line the pipe can go up, down and sideways as long as it's below the water line it doesn't matter