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CO and venting

Bob HarperBob Harper Member Posts: 732
We all play the game of risk. A unit operating with o2 & CO2 in the groove can kill you if you block the chimney, rot out the HX, depressurize the CAZ or any number of things. However, as the potential goes up, society places greater constraints on us. Look at the building codes. As you place hazardous materials in buidlings, the construction and safety features such as sprinklers and forced ventilation escalate. Left alone in containers, these materials may not represent a direct hazard but the codes still require extra protection just in case. So too with combustion a degree.
Explain to me why a gas direct vent fireplace cannot exceed 25ppm air free flue gases while a ventfree gas oven gas hit 800ppm air free. The one more protected against negative forces such as depressurization and wind gusts is slapped with an unfair requirement. Meanwhile, you thought it was the tryptophan from the turkey making you sleepy at Thanksgiving. So, why not lockout the oven at 799ppm? It's all a game we play. The gas utilities have their own tariff with the State that empowers them to do what they want. They can come in and shutdown anything they feel like or conversely ignore whatever they feel like based upon the Just Cause principle, which states they can do what they want Just Cause they feel like it.
Which are you going to TagOut & Lock Out: a furnace that passes a Worst Case Depressurization Test with -5 Pascals in the CAZ and a stack air free CO of 250 or a Cat. I fan assisted furnace with a stack are free CO of 12 but it is common vented with a draft hood equipped water heater. Which poses the greater immediate threat to the homeowner if both vent into masonry tile 'lined' chimneys?


  • MitchMitch Member Posts: 549
    CO and venting

    I am going to be more specific than my last thread that I started.

    1) Gravity boiler with normal co venting properly that
    then has a venting issue (blocked flue unseen terracotta
    section becomes loose and falls accross the breach)
    what happens.

    2) Gravity boiler with high co venting properly with
    no foreseeable venting issues ever (beautiful stainless
    liner and cap).

    #1 will start making high co as co2 changes the o2 ratio. At a minimum the lack of proper draft will change the combustion rate due lack of 02 being brought in.

    This will start making higher levels of co at an excelerated rate filling the house with a deadly gas.

    #2 was always making high co, venting to they sky. Never bothering anyone

    Explain to the home owner why a boiler making high co but venting properly is such an issue even though it has been installed for years and never a problem?

    Stay strict to the topic on this one I do not want to hear about safety's on the equipment.

    The basic premise is a properly vented appliance has not been a problem regardless of co reading. An appliance with a normal co reading will change if the vent becomes compromised so any combustion test is usless if there are changes after the test. Don't give me any "steady state" issue either.

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  • Mark HuntMark Hunt Member Posts: 147
    High CO

    Fuel economy.

    CO is a by-product of incomplete combustion. If the fire isn't right, the customer is paying higher fuel bills.

    Mark H
  • TimcoTimco Member Posts: 2,814

    In my gas cert class, they talked about max allowable levels of CO and NOX. Why knowingly be part of the pollution problem the US has? High CO means something ain't burning right, period. What about windy conditions? Small amounts of high concentration CO being leaked in???

    Working on steam and hot-water systems isn't rocket's actually much harder.
  • Bob HarperBob Harper Member Posts: 732

    If the system is venting properly and there is no ambient CO, then there is no immediate hazard to the occupants. The high CO in the stack represents and increased threat should there be an insult to the venting so you have greater potential for a hazard but none directly.
    The problem with "operating properly" is this is a snapshot in time. Was this determination based on a Worst Case Depressurization test or just walking in and taking some readings? Was it tested in summer or winter? What was the wind speed and direction that day? You see my point? We can never take into account every variable. What is important is to recognize what is reasonable such as in the Worst Case scenario. It is reasonable to assume there will be a day when both the air handler and clothes dryer are running concurrently with the water heater/ boiler/ furnace.
    The ANSI stds. apply to testing in vitro or in the lab---not in the field. There is no legal performance requirement in the codes for combustion equipment to meet certain parameters. Even the issue of testing is not properly addressed in the codes but it should be.

    Mitch, as for 'changes' in the venting, that's why all heater flues should be listed liners, vents or chimneys. Terra cotta tile is an obsolete material that can and does fail regularly. That' why the codes require cleanouts--for planned failure.

    good thread!
  • MitchMitch Member Posts: 549

    You are on my track so why do we shut down a perfectly venting appliance at 401 ppm.

    The 35 ppm has the same risk factor if the venting changes and co2 enters the combustion air as the appliance vents into the room.

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