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Oversized Boiler?

ksd99 Member Posts: 77
Ive n]been in my house 3 years and I’ve learned a lot about my boiler from this site, it running just fine with no banging or noises - I’ve worked thru them. Bu the 1 thing that happens is the water level in the sight glass always drops more than an 1’’ while running. I thought it needed to be skimmed so I had port put on it and I skim it a few times a year if need be, but the drop always happens. A heating company a few years ago told me my ‘dry returns” aren't leveled right and the water is taking more time to return to the boiler. So for the heck of it I filled out the sizing chart and my radiators equals 158,832 BTUH, and on my boiler it states BTUH INPUT 262500. I don’t experience any other issues - no hammering etc. thoughts?

New owner of 1 Pipe Steam Boiler - learning all I can- no real steam pro in S.W. Michigan - if you know of 1 -let me know.


  • Jamie Hall
    Jamie Hall Member Posts: 23,286
    If it ain't broke, don't fix it. Time to worry about the sizing when and if you need a new one.

    The dry returns should be pitched to drain, but it doesn't have to be radical. Half an inch in ten feet is likely to be ample.

    It's not at all uncommon for the water level to drop slightly when the boiler is steaming, so long as it is reasonably stable. If your dry returns are vented -- as they must be -- the boiler pressure is going to push water back up any drips to balance the steam pressure. Particularly on smaller modern boilers, this may be enough to show -- not to mention the steam which was water and is now out there wandering around in the pipes and radiators.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • acwagner
    acwagner Member Posts: 505
    edited January 2021
    Regarding the size of your boiler--the input value is the gas that goes into the boiler, not what's available for the radiators. The boiler probably operates at around 80% efficiency, so the 262,500x0.8 = 210,000 BTU per hour is available for the system (the rest is lost up the chimney). There's also an allowance for heating up the distribution piping and some extra for startup. Rule of thumb is 33% for that (opinions vary on this). So 210,000x.67 = 140,700 BTU/Hr is available for your radiators. So it looks like you are right sized based on the conventional approach, especially if your piping is mostly insulated.
    Burnham IN5PVNI Boiler, Single Pipe with 290 EDR
    18 Ounce per Square Inch Gauge
    Time Delay Relay in Series with Thermostat
    Operating Pressure 0.3-0.5 Ounce per Square Inch