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Combustion Fumes

that the vent on the gas valve regulator corroded over causing the regulator to fire the burners at street pressure, about 6". Caused the face plate on the HX to crack in a few places. It was a 48TJE unit with White Rodgers gas valve.


  • JimGPE_20
    JimGPE_20 Member Posts: 7
    For our CO experts....

    Just got a call from a client's office building. They said that they had combustion fumes in the office space. Yeah, that got my attention. My wife works there.

    Jumped in the car with my CO Experts CO detector. With the detector in the space with the worst odors, no detected CO after 1/2 hour. Push the button, and it says zero CO, peak zero CO. They had not ventilated the space between when they called and when I arrived.

    Went up on the roof, discharge port on the combustion drafter fan is sooted up pretty badly. None of the other identical units on the same natural gas line is sooted up - this is the only one with soot. All units are on the same gas line within 50' of each other.

    Prevailing wind (about 10 MPH) is blowing the combusion gas directly away from the outside air intake. Odor goes away when you run the fan without the heat on.

    Called Carrier tech service. They said the only adjustment possible for combustion is the gas pressure. No air shutters, for instance, a fact that I visually confirmed.

    Said the gas valve has a built-in regulator. Said the pressure down stream of the gas valve should be regulated to 3.5". Chances are the pressure is too high.

    I have a service guy scheduled for Tuesday to yank the heat exchanger, examine it for leaks, clean it, re-seal the joints between the combusion air and the airstream and adjust the burner pressure.

    And I am leaving my CO Experts detector in the space all weekend.

    Anything else I should be doing?

    This is a Carrier 48TFE005-M-511 HQ, manufactured in 2002.


  • Mark Hunt
    Mark Hunt Member Posts: 4,909
    Not much more

    you can do other than monitor the space.

    It sometimes takes hours, days or even weeks to get a situation to repeat itself.

    Mark H

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • JimGPE_20
    JimGPE_20 Member Posts: 7

    Thank you, Mark. That makes me feel better!

  • Larry Savino
    Larry Savino Member Posts: 63

    I am not positive on the model number but if its the one with the tubeular heat exchanger look for rust hole where the in shot burners hit the first bend in the heat exchanger. we have Found lots of pitted/pourus ones but the unit is designed so that the heat exchanger is on the positive side of the air stream so if it was leaking the blower air would push the flames back intto the heatexchanger causing tthe unit to open on flame role out.

    I know you can never be too safe with CO but if your reading are good I just cant think how this unit could bring CO into the building,Unless it has an economizer on it and one of the other units were calling for heat and exchausting by this unit and it was in a fresh air mode or calling for free outdoor cooling.

    Good Luck
  • JimGPE_20
    JimGPE_20 Member Posts: 7

    I thought of the economizer angle myself. There is one unit that could be blowing some exhaust into the OA intake, but there was good correlation between the unit in question running in heat and having the smell and the unit in question running fan only and no smell. There was no correlation between the smell and the other unit on heat.

    Thanks for the tip - I'll have the field guy start there.

  • David_5
    David_5 Member Posts: 250

    The fumes get drawn in through the economizer or manual fresh air damper.

  • Tom Shekita
    Tom Shekita Member Posts: 17

    Please forgive a novice! Are they sure they are smelling "unburned exhust" or has someone been painting/staining nearby?
  • Empire_2
    Empire_2 Member Posts: 2,343
    Inshot burners

    Provided the heat exchanger is not cracked or pitted, chech the cross over plates on each burner to assure that they are clear. Also pull burner orifice to make sure a spider hasen't built cacoon inside. I have found it before and if you could at least give the exhaust a quick smell with and without fan, that can give you an indication of heat exchanger problems. Since the blower door is next to the exhaust and is really not 100% sealed, the intermittant problem may be getting into the unit that way.

    Just my thoughts.
  • JimGPE_20
    JimGPE_20 Member Posts: 7

    No paint, no stain, (both good guesses) and no, I am not sure it is exhaust. After two days of monitoring, zero CO from a unit that is sooting up, so I am pretty much convinced it is not sucking in exhaust fumes.

    Next best theory, something crawled up into the heat exchanger and died. It is now being incinerated by degrees....
  • JimGPE_20
    JimGPE_20 Member Posts: 7

    Was up on the roof with the service guy today. Gas manifold pressure was twice what is needed. Backed out the adjustment on the regulator and voila! no more fumes. Even the exhaust on the roof smelled markedly better.

    Thanks for all your input.
  • John Starcher_4
    John Starcher_4 Member Posts: 794

    ....we try to out smart ourselves ;-)

    Amazing how many times it's something simple, ain't it?

This discussion has been closed.