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  1. #1
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    I am deciding between two contractors for my new A/S or Trane furnace. One says that he will check and adjust the gas pressure on the 2 stage gas valve. The other says that he can do the same but usually does not since it is very unusual to have to modify the gas pressure on the gas valve on a replacement furnace. I would like to know if the gas pressure adjustment is commonly done at start up or is the valve's factory adjustment usually within the acceptable range.

  2. #2
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Check it every time.

  3. #3
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    You must check and adjust the gas pressure, period.
    Karst means cave. So, I search for caves.

  4. #4
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    Thanks for your replies. Is the pressure measured on the supply gas pipe and at the valve? What is the purpose of the pressure check and what is the danger of not checking it? Could someone tell me what should be checked at start up? Do manufacturers require some sort of start up sheet be filled out to qualify for your warranty?

    [Edited by heetseeker on 06-15-2005 at 10:56 PM]

  5. #5
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Check the pressure at the manifold of the furnace. Different gas meters can have different degrees of pressure delivering to the furnace. You must check the gas pressure to ensure it is set to the factory numbers. I have seen furnaces grossly overfired right from the factory. Only takes a minute or two to check. Better safe than sorry.
    "Go big or Go Home"

  6. #6
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Just wondered what even brought this subject up with these contractors. In all the years I have been doing this nobody has ever asked me if I check the gas pressure. I would assume this was only one of many questions asked by you from a list?

  7. #7
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    Trane
    You are correct about me asking a lot of questions. I am trying to decide who I should have install my furnace and heating equip. This forum mentions many things that are a sign of a quality install. So far I have not found a contractor that does a true manual J, has any interest in improving my return ducts, uses nitrogen to braze,uses mastic on ducts, uses a micron gauge or air balances using a flow hood. One of the contractors mentioned that he will check the gas pressure as part of the install so I asked the other contractor if he does also. I would like to know the danger of not checking. Is there startup checklist that every quality install should check?

  8. #8
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    Some furnace manufacturers include a start up check list in the install manual. I know very few contractors who actually use these manuals. (I am guilty on occasion as well). It lists things to check on initial start up, these include checking: fan speed, temp. rise through the heat exchanger, gas pressure, motor amp draw etc... I would say that most furnaces are fine as they are right from the factory but temperature rise should always be checked.
    "Go big or Go Home"

  9. #9
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,514

    Perfect Furnace?

    It is impossible to perfectly duplicate mechanical parts. Burner orifices would have to be drilled under a microscope. Gas BTU's per cubic foot vary all over the country by as much as 10% at sea level and much more above 2000 feet. More important than gas pressure it is critical that a combustion analysis is taken that can varify the actual mechanical operation. Every furnace operates slightly different based on the venting system, the duct system, the BTU's of the fuel and its own mechanical inconsistencies. Nothing is guaranteed until it is checked!
    captain CO

  10. #10
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    While all these things should be checked, I seriously doubt that even 1 in 50 furnaces have there pressure checked or combustion checked. I have almost never seen anyone check out a new furnace to that extent unless there was a problem right out of the box. Unfortunatly as everyone on here knows, a lot of people are way to busy to check up on how good a job was done at the factory. In most cases it is not until after the first PM is done on a unit that gas pressures etc.. are checked. Wish it could be different but that is the way it is.
    "Go big or Go Home"

  11. #11
    Join Date
    Dec 2002
    Location
    peoples republic of maryland
    Posts
    958
    Check it EVERY time, however I've noticed that Trane's (american standard) has been very close if not right on out of the box.
    "The meek shall inherit the earth"
    "he that's walking with wise persons will become wise, but he that is having dealings with the stupid ones will fare badly" Proverbs 13:20
    "Pressure is something people feel when they don't know what their doing". Peyton Manning-superbowl MVP

  12. #12
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,514
    Originally posted by md master
    Check it EVERY time, however I've noticed that Trane's (american standard) has been very close if not right on out of the box.
    Most of the Trane and American Standard Contractors that I have worked with have said these furnaces are off 20% to 25% on their rated outputs when they do a combustion test. But this is fairly standard for most furnaces. It is a safety factor that manufacturers build in because they sell to many that don't have time to do the job right.
    captain CO

  13. #13
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    Thanks for the replies.
    Jim, are the a/s trane furnaces putting out 20-25% less BTU than their rated output. How is this a safety factor? Is this to prevent an overfired condition that increases CO?
    Black Adder,
    I have had my furnace checked many times but no one has ever checked the gas pressure . Is that common in Canada?
    Why is the check of the heat rise important? Is it to keep the HX from cracking at too high a temp? Won't the limit switches protect the HX.
    Is adjusting the gas pressure something that is done on the valve so the burner orifices see less pressure?

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