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How much is 1 PSI?

HarryL Member Posts: 59
More than I thought, that's for sure.

I haven't seen the pressure gauge (0-5 psi) budge this winter and last year was so mild (Boston) that I never really paid much attention to the system. I thought the pigtail was clogged so I cleaned that and the piping attached to it. Still nothing on the gauge as the system cycled. So I popped the gauge off, put some tape around the threads, and blew. I moved the needle to 1.5 PSI or so, but I was surprised how much effort it took. I thought maybe there was a problem with the gauge but after googling around 2 PSI looks about right for the human lungs.

Home owner, 1927 2-story, single family
1 pipe Burnham IN4I, Boston area


  • Jamie Hall
    Jamie Hall Member Posts: 22,877
    Amazing how small a pressure differential a properly functioning steam system works on, isn't it?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,477
    edited February 2021
    How much is 1 PSI? I thought this was a trick question. I would usually say about a buck, two-eighty!
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • lockdown_lou
    lockdown_lou Member Posts: 15
    Apparently 1psi is a lot to my 1-pipe steam system.   I’ve had the 1896 house for two seasons.   18 rads,  new EGH-95 boiler last summer,  all new wet returns, house heats well. 

    I just installed a 3psi low pressure gauge and even on a cold day (20F) at 1 cycle per hour the boiler gets to MAX 0.15 psi, (2.4oz) before the thermostat shuts off.  About 15 min of run time.  House is toasty.  Apparently the new boiler isn’t oversized,  which is nice. 

    So for fun the other night I installed a Big Mouth vent on a slow main and cranked the thermostat from 69 to 74 to test it out and make sure the big mouth closes, and the whole system ran for a whopping half an hour.   The low pressure gauge got to 0.5 psi.  And when I went upstairs into living room,  all the Heat timer varivalves were sizzling hot and leaking and  ALL the packing nuts on the radiators were hissing like hell and dribbling water all over.    So I guess I need to repack everything.   Nothing ever hissed or leaked water before.  And this is at 0.5 psi.

    And here I thought people on this board were nuts when they said vari-valves don’t close correctly.  The maid o mists and gortons didn’t leak at all. 

    It also explains why I use a gallon per week of makeup water in solidly cold weather.  

    Guess it’s really good the system runs at low pressure as it’s going to be a pain to fix all the steam leaks in April!
  • ethicalpaul
    ethicalpaul Member Posts: 5,573
    Blowing into gauges and pressuretrols give a great understanding of the pressures that our systems see. I highly recommend it
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el