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Armstrong ultra 90

rerun123rerun123 Member Posts: 7
i have a armstrong ultra 90 model number guk075d14-3a 75000 btu that i am trying to convert from propane to natural gas i need to know the orfice size for natural gas any help please


  • IronmanIronman Member Posts: 5,825
    You need to get the conversion kit from the manufacturer. There's more to it than just the orifices and unless you're a qualified gas technician, I wouldn't recommend that you attempt it.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • rerun123rerun123 Member Posts: 7
    i have a gas tech and we have contacted armstrong and since it is 22 yrs old they have no information on it this furnace even though it is 22 yrs od has been used very little since i have an outside wood burner i just got natural gas
  • rerun123rerun123 Member Posts: 7
    and yes he can get the valve converted
  • rerun123rerun123 Member Posts: 7
    and by the way it has number 54 propane orfice if that helps
  • SlamDunkSlamDunk Member Posts: 875
    edited October 15
    Armstrong's response is a polite way of saying you need a more experienced gas tech. It is simple math using pressures and btu content to figure out new orifice size. There is even a rule of thumb to ball park it. If your gas tech doesn't know the math, or the rule of thumb, he is under qualified.
  • rerun123rerun123 Member Posts: 7
    thanks for your reply and he might be but he is who i have so f you could pass that math solution on it would help him and really help me i am old and need this done thank you very much for any help you could give
  • rerun123rerun123 Member Posts: 7
    Thanks for all your help for this old retired army vet
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