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  1. #1
    Join Date
    Jul 2009
    Spokane, WA

    Default CO detected at supply registers

    Back to back inspections where I got CO levels at the registers. I have never found this condition before and have a couple questions. The first furnace is a 80% Armstrong Air. The unit is only 2 years old. So I watched the flame pattern at the time that the blower turned on and the flame pattern changed. Before it was nearly solid blue. After there were flashes of yellow/orange. I took readings at the closest register and got 3 ppm CO. The second furnace is 41 year old Luxaire with draft hood. I got 3 ppm at the closest register as well. So here is my question. Is there any other condition besides a failed(hole) heat exchanger for CO to be detected at the registers? I know that 3 ppm is not a significant amount but this number should always be zero right? I also noticed regarding the 41 year old Luxaire that while taking a reading at the register, the temp of the register itself was 155 degrees. Seams to me that if water temp over 120 is a safety hazard, then a register at 155 would be also, My second question is regarding forced air temp, what is considered the normal operating temp at the registers and at what temp do you call it out as a safety hazard? Also just for my own knowledge, what is failing at the furnace to allow for 155 degree air? Thanks in advance for the help.

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  2. #2
    Join Date
    Mar 2007
    Near Philly, Pa.

    Cool Re: CO detected at supply registers

    These units need professional combustion analysis. I would not get into taking readings at supply registers, which can be useless. Aside from the calibration issue, you don't know what is producing the CO from a reading in a register.

    For one, flue gases can shunt from the burner compartment back into the blower compartment if it is not absolutely air tight.

    Most units publish a maximum supply plenum temp, which is usually in the range of 155-170. Check the rating plate.

    Call for a qualified professional who is certified in CO and Combustion analysis.

    At 41 y/o they got two lives out of that unit.

    Keep the fire in the fireplace.


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