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Oversized Boiler?

Rory
Rory Member Posts: 7
Bought an old brick house with a Burnham 5b on a 2 pipe system with Hoffman traps and a dry return. Boiler installer had the pressuretrol set at 3psi with a 1psi differential. Heating bills were on the high side, so I decided to experiment by turning it down to 1.5. I haven't measured the EDR yet, but I have a suspicion that the boiler is oversized. There are air vents on the 3rd floor radiators to help with distribution. I can hear the vents whistle when the burners kick on, but the burn cycle is now so short that right before the steam gets up there the burner shuts off and they start drawing air back in. My burner has no means of regulation, so I can't turn the flame down any... just on or off. I think what's happening is I've got too hot a fire, so I reach the set pressure very quickly. Is there any cheap way to add some level of control to my burners to extend my cycle time, or am I just stuck with a higher pressure setting? 

Comments

  • Rod
    Rod Posts: 2,067
    2 Pipe System Problems

    Hi- Before coming to the conclusion that the boiler is over sized we need to know more about your system. Generally on a two pipe system you shouldn't have vents on the radiators. Are all the radiator heating properly? Are all the steam traps working ?   On the end of the steam main(s) is there a pipe connecting the steam main to the return main? If so is the trap on the connecting piep working properly.  If there is no connecting pipe, is there a vent and a drip line down to the wet return at the end of the steam main?  Are there main vent(s) on the return main? If so are they working properly?    It would help a lot if you could post some pictures of your system. Pictures of things like boiler and connecting piping and  main vents help a lot.

    - Rod
  • Rory
    Rory Member Posts: 7
    Oversized boiler?

    The radiators heat well, all the way across unless the thermostat is set very low. Then only about halfway across on the second floor. Traps were all replaced at the same time, about 5 yrs ago. I've not come across any hot condensate lines, or heard any traps that sound like they're passing steam. I'd have to look at the end of the steam main again when I get home to see how it's connected to the return... but I do know there's a vent at the end of the return. I'll post back again with some more info.
  • Jamie Hall
    Jamie Hall Member Posts: 15,355
    Whoa there!

    Before you start worrying about the boiler -- worry about vents!



    There are at least two possible ways this thing was vented originally: either with crossover traps from the steam mains to the dry returns, and then the dry returns vented (big vents) (possibly all tied together) at the boiler (this is more likely) or with big vents at the ends of each steam main.  The former setup is somewhat more likely to have been the original.



    First thing -- look for main vents in the basement.  As I note, these should either be at the boiler on the dry returns, or at the end of each steam main.  If they aren't there, or aren't working, they need to be replaced.



    Second, if there are main vents (or were!) at the boiler, go looking at the end of each steam main: there should be a crossover trap -- just like a radiator trap, but possibly bigger -- at the end of each steam main.  These exhaust into the dry returns.  If these are failed closed (or have been removed!), they need to be repaired.



    There should be no need for vents on any of the radiators; it sounds very much as though someone knuckleheaded this system and, having messed up the main venting then went and tried to fix it with vents on the radiators -- which is not likely to work well.  Radiator vents just don't have the capacity.



    Fix your main venting first.  Then take another look at the cycling of the boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Rod
    Rod Posts: 2,067
    edited February 2012
    2 pipe Steam Systems

    Here's a diagram to go with what Jamie is mentioning.

    - Rod

    Edit:  I loaded the same diagram as a PDF as it maybe easier to view it that way.
  • Rory
    Rory Member Posts: 7
    Smoking gun...

    Got a halogen pointed at the boiler yesterday, and found that the end of the main is tied to the end of the return. The return is vented at the boiler with a Hoffman 4a. The main has NO trap between it and the return. Just a leg that drops down (but not below the water line) and comes back to join the return just under the vent. Looks like I'm probably pushing live steam into the return in order to vent. Probably why I get some hammering in that area on a cold startup. Further investigation revealed a spot on the main where there should probably be a vent, drumroll... pipe plug.
  • Jamie Hall
    Jamie Hall Member Posts: 15,355
    Which makes me wonder

    where the water line on the original boiler was...  I'll bet that return to main connection was originally below it, and a smaller (physically) boiler was installed without checking to match the water lines.  Happens pretty regularly.



    Can you just lower the connection and hook it into a wet return?  Should make some difference!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • Rory
    Rory Member Posts: 7
    edited February 2012
    Wet return

    I think they tried to copy what was there without any regard to the water line... Looks like if I drop the horizontal section between the main and the return down below the water line I'll be creating a wet return. (not seen in the photo is where it connects to the loop through what looks like a check valve.) All this after replacing the vent on the main, of course. Otherwise, the only piping below the water line is the loop.
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