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How to tell if boiler is over firing?

Mike K_10
Mike K_10 Member Posts: 4
I have a newly installed W-M steam boiler. I'm wondering if it might be overfired. The water in the sight glass is still surging somewhat, even though it has been skimmed several times. The water is pretty clear, but still a little surging, and the air vents seem to get a lot of water in them, causing clogging of the air vent. The diagram in the manual, showing how the flame should look when properly fired, isn't too helpful. Any suggestions?


  • ed wallace
    ed wallace Member Posts: 1,613
    boiler over firing question

    can you post pictures of the new boiler and the piping that was replaced it sounds like you have other issues other then boiler over firing
  • Frank_62
    Frank_62 Member Posts: 16

    if you have water in the vents your dragging it up from the boiler probably. from the center of your sight glass to the bottom of the header should be at least 24 inches or more. How many risers (pipes coming out of the boiler to header) do you have and at what diameter compared to what you replaced. new steam boilers don't have as big of a steam chest as old ones so velocity of the steam plays a big part. look at your manual it should show you piping specs if it doesn't match and dimensions are smaller discuss it with your installer,check pressure settings and main vents the boiler fire against the load (radiators) is it big enough to acommodate existing edr is it to big? edr on rating plate (most manufacturers add the 33%pipe factor into the stated edr) pics would be good consentrate on what got changed since it was fine before good luck
  • Elias
    Elias Member Posts: 22

    Determining firing rate is a fairly straightforward equation of input/output. Your steam making capacity is determined by how much steam that you can condense. This is detailed in "The Lost Art" available on this site. You will measure the amount of radiation (the "load") and add a pickup factor, to account for heating up the piping on startup. The book can't be recommended enough, it's all in there. If you are firing oil, and want to downfire, gross BTU output is determined by multiplying the gph of the nozzle X 140,000 BTU (or thereabouts, the heat content of heating oil is usually computed from 136K-140K, depending on region) and then multiplying by steady state efficiency which ought to be around 82-84%. This gets you to right about the "gross" output. It's all in the book, chapters devoted specifically to boiler sizing, and nobody explains it better than Dan H.

    You can get spitting vents even with good near boiler piping and proper firing rate if you vent too fast. Try to vent the mains very quickly, the risers quickly (but too quickly can also give you spitting radiator vents, especially if the risers aren't dripped) but try venting the radiators slowly but fully. Insulate the mains, if they aren't!

    Again, it's all in the book. It's so good it makes being a shill a real pleasure.
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