Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

LP gas pressure drop

kcopp Member Posts: 4,188
Installing a Combi boiler in a home today.
Fire up the unit and gas pressure is @ 11.1 in wc.
Goes into high fire and it drops to 8.5" wc.
I don't do a huge amount of LP work but that sounds excessive?


  • lchmb
    lchmb Member Posts: 2,997
    edited October 2016
    yes...sounds like either your piping is undersized or an issue with the regulator. (wouldnt want more than .5" drop in pressure)
  • kcopp
    kcopp Member Posts: 4,188
    Piping is 25' on 1/2" should be fine for 125K....
  • njtommy
    njtommy Member Posts: 1,105
    Whats the min max range say in the manual?
  • kcopp
    kcopp Member Posts: 4,188
    7-14 at start... only 1-2" drop.
    NFPA refers to only a 1/2" pressure drop in all the LP stuff.
  • Jamie Hall
    Jamie Hall Member Posts: 21,106
    How big is the boiler and how big is the tank? Any possibility that evaporation rate in the tank is being exceeded by the demand?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • kcopp
    kcopp Member Posts: 4,188
    Boiler is 125K in. Tank is huge... Its a condo w a meter.
  • Zman
    Zman Member Posts: 7,446
    I had a similar problem that drove me nuts for a while. The pressure would drop to 4" to the whole house when the boiler fired up. Any other load would not drop the pressure at all.
    I swapped out the house regulator and it was fixed.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    delta T
  • delta T
    delta T Member Posts: 883
    My money is on the reg. Usually the first thing I go to anymore when I see this problem on LP.

    25' of 1/2 should be plenty for 125k, so you should be seeing a drop of less than .5"