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  1. #14
    Thanks for all the info, It is a lot easier to troubeshoot a problem with the right info, although I do not understand some of the info that you have stated, I'm hearing that you having a condensing problem in the attic space and that it is also on the inside of the vent and not the outside, how are you confirming that it is condensing on the inside of the flue running through the attic, how can you tell ? if it is running I'm sure you are not looking into the vent and if it is not running and you look in and see moisture then the pipe is getting very cold very fast after shut down, are you sure that this is a double wall pipe ? and is the water heater flue common to this vent maybe we are looking at the wrong appliance ? also are there any bathroom, kitchen or laundry exhausts vented through the attic space or into them. As for the numbers you are reading they are not the best but they are also not the problem seem to be a little short on combustion air. Did you get a CO reading in your attic because in many cases that I have seen where a furnace was emitting fumes with CO into a living space the spaces also had a high content of moisture in the air, comes from burning gas I would also like to know if your house is in a negative pressure go crack your door open slightly hold a kleenex there and see if it wants to drift in or out of the house. Thanks

  2. #15
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    [QUOTE]Originally posted by pipedope

    the high o2 number could also be due to a cracked heat exchanger i haven't seen many gas units run a 6% o2 most of the time it is between 8-11%.
    The O2 number would have to increase after the blower comes on to indicate a breech in the heat exchanger. Unfortunately we don't have access to those readings.
    Pipedope on a furnace that is running 8%-11% O2 it is probably a tad bit underfired.

  3. #16
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    Originally posted by fat eddy
    As for the numbers you are reading they are not the best but they are also not the problem seem to be a little short on combustion air.
    Eddy,how did you determine he was short on combustion air from the readings that were given?

  4. #17
    Join Date
    Dec 2004
    Posts
    21
    Thank you all for your help.
    fat eddy:
    It is double wall b-vent pipe and it leaks in joints in the attic. I have also checked with kleenex and the drift is inbound to to the home.

    davidr:
    what causes the under firing? How to decrease the O2 level?

    I am not sure whether I am still having short cycling. When I monitered it, the fire stays on for only 3 minutes and the blower continues to run for 2 minutes after the fire. so the total cycle is 5 minutes. Is this normal?

  5. #18
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    Originally posted by sanrishi


    davidr:
    what causes the under firing? How to decrease the O2 level?
    Not enough gas. Increase firing rate. Add gas


    I am not sure whether I am still having short cycling. When I monitered it, the fire stays on for only 3 minutes and the blower continues to run for 2 minutes after the fire. so the total cycle is 5 minutes. Is this normal?

    Did the tech check the heat anticipator to see if it was set properly on your thermostat if it is not digital.
    If it is digital it may not be configured properly.
    It could also be that the thermostat is being satisfied,any supply outlets close to the thermostat?

  6. #19
    Join Date
    Dec 2004
    Posts
    21
    davidr:
    my thermostat is digital programmable honeywell thermostat.
    Should I configure the digital thermostat?
    An electrical supply outlet is within 2 feet range. Can it cause anything?

    thank you.

  7. #20
    considering that no wind is blowing it in it would sound as though your home is running in a negative pressure, as for the leaks in the attic I'm assuming that you have condesation leaking through a joint and running down the outside of the pipe, this is not typical of the configuration of a b-vent although not waterproof it is usually a pretty tight connection. both these problems need to be properly addressed a house should never be in a negative pressure and your attic is probably freezing because it is, If you have a fireplace check to see if the damper is shut, then turn off any equipment you may have running that is exhausting air from your house. Check to see if you can find any soure for combustion air entering the furnace room.

  8. #21
    I figured it was short on combustion air, not from those readings. I'm not considering any of those readings other than the stack temp. I have no idea what condition that guys meter was in and if he couldn't get to the problem I am not going to assume that he has ever used that thing with any success or even had it calibrated in this century.

  9. #22
    Join Date
    Apr 2002
    Posts
    11,808
    That high of O2 is consitent with the amount of excess air (162%). It is probably under fired like davidr is saying as opposed to an inducer sucking way too much air.

    As fat eddy says the guy should have clocked the meter.

    It is not that big of a furnace, I would wonder if the anticiaptor setting is wrong or if a cold draft is influencing the thermostat.

    The OP's response to fat eddy says the house is negative, maybe cold air is getting pulled down a wall cavity and influencing the stat.

    Probably has about a six inch b-vent, too much surface area, causing the condensation problem. Vent tables may require a 4 or 5 inch depending on height, water heater etc.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  10. #23
    I'm also not sure if the readings were taken before or after the gas pressure was turned down.

  11. #24
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    Originally posted by sanrishi
    davidr:
    my thermostat is digital programmable honeywell thermostat.
    Should I configure the digital thermostat?
    An electrical supply outlet is within 2 feet range. Can it cause anything?

    thank you.
    I should have clarified what I meant by supply outlet.
    I meant a vent that is blowing warm air from the furnace into your home,sorry for the confusion.
    On the thermostat you should check the installation manual to see if it needs any further setup for a gas furnace.

  12. #25
    Join Date
    Oct 2001
    Location
    Waterford Michigan
    Posts
    2,668
    If he said the firing rate and temperature rise are within manufactures specifications I’d call another contractor for a second opinion.

  13. #26
    Join Date
    Dec 2004
    Posts
    21
    Originally posted by fat eddy
    considering that no wind is blowing it in it would sound as though your home is running in a negative pressure, as for the leaks in the attic I'm assuming that you have condesation leaking through a joint and running down the outside of the pipe, this is not typical of the configuration of a b-vent although not waterproof it is usually a pretty tight connection. both these problems need to be properly addressed a house should never be in a negative pressure and your attic is probably freezing because it is, If you have a fireplace check to see if the damper is shut, then turn off any equipment you may have running that is exhausting air from your house. Check to see if you can find any soure for combustion air entering the furnace room.
    hi eddy,
    I think that you misunderstood what I have said in my previous post. When I tested with kleenex, it was drifting in. So, it means that wind is blowing in. Right? Is this negative pressure?

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