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Steam system efficiency

Ok so back story. I purchased a house that came with a weil mclane 114k switched from oil to natural gas via riello f3 burner. Previous owner was running the burner at 86k so I switched over the orfice to burn at 114k. Was still having some issues getting steam. Switched all the radiators over to gorton air vents and the 2 mains to big mouth vents which cut the heating cycles to about 31 minutes from 47. Fast forward to this year the riello crapped out and instead of replacing the riello i opted for a slant fin galaxy 120. Replaced all the header and Hartford loop with black steel according to slant fin and dead man steam (previous was mix or copper and brass with no dielectric unions). Now my question is my boiler does not make pressure rather it satisfies the stat. According to my dc710 analyzer it's running at 86 percent efficiency. So my thought is the big mouth vents are allowing too much air out to build pressure. Which is more effective more air out and satisfying the stat or building pressure and satisfying the pressuretrol?


  • If all the radiators get hot, (even partially), then that is all that is needed. You are lucky not to have any more pressure than enough to push the air out, and get steam to all radiators.
    Satisfying the thermostat should always be the goal.—NBC
  • Fred
    Fred Member Posts: 8,542
    A properly sized boiler should not build any more pressure than is needed to deliver steam and should not build enough to trip the pressuretrol. If it satisfies the thermostat, you are good.
    All the air needs to be removed from the Mains. The Bigmouth or any other Main Vent can't vent too much air. They have to vent all the air for a balanced system.
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    No pressure is needed. Vapor traveled faster and heats more evenly. As it condenses, steam generates a vacuum that helps move the steam forward. There no pressure required at all.

    The big mouths allow a better ratio of main venting to radiator venting. You only need enough venting to remove air at the rate the radiators heat up at the pressure differential provided. Even 0.1” is enough pressure to move plenty of air.

    My 200k input boiler is undersized to the load but I have slow enough radiator venting to control it. Pressure never registers on a 8oz gauge. I’m guessing it runs around 0.1” and I need to re-zero the gauge.
  • ethicalpaul
    ethicalpaul Member Posts: 5,617
    What they ☝🏻☝🏻☝🏻 said, if you need another vote 😅
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • It would be wise to add up the EDR of your radiators and compare that to the rating on the boiler, now that you have enlarged the oil nozzle.—NBC
  • Steamhead
    Steamhead Member Posts: 16,734

    What they ☝🏻☝🏻☝🏻 said, if you need another vote 😅

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • dopey27177
    dopey27177 Member Posts: 887
    When you are speaking about efficiency there are two kinds.

    1. burner efficiency which only tells you how efficient your burner is operating. That's your combustion efficiency
    2. Boiler efficiency is another issue, Nearly all steam boiler operate at 80 to 90 % efficiency most of them at about 82 to 85 % , unless equipped with reheat coils for producing hot water or minor heating m=needs. These coils are installed in the chimney or near the breaching of the boiler. That increases your overall efficiency not the boiler efficiency.

    The 86% efficiency you are getting is reflective of your heating system heat transfer efficiency. You have just about reached Nervana.

  • Jamie Hall
    Jamie Hall Member Posts: 22,947
    Or to put it another way: building pressure in a heating system -- particularly through restricting venting -- is exactly comparable to driving your car with one foot on the gas and one on the brake pedal. Not good.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England