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LP gas pressure drop

kcoppkcopp Posts: 3,355Member
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?


  • lchmblchmb Posts: 2,946Member
    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)
  • kcoppkcopp Posts: 3,355Member
    Piping is 25' on 1/2" should be fine for 125K....
  • njtommynjtommy Posts: 1,104Member
    Whats the min max range say in the manual?
  • kcoppkcopp Posts: 3,355Member
    7-14 at start... only 1-2" drop.
    NFPA refers to only a 1/2" pressure drop in all the LP stuff.
  • Jamie HallJamie Hall Posts: 11,195Member
    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?

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • kcoppkcopp Posts: 3,355Member
    Boiler is 125K in. Tank is huge... Its a condo w a meter.
  • ZmanZman Posts: 5,262Member
    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 Tdelta T Posts: 785Member
    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"
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