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  1. #14
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    70,417
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    Not piping combustion air to the outside is also one of my pet peeves, but so many techs just don't understand all of the "why's" for things we should be doing, so they cut corners because the equipment manufacturer says they can.

    Outside combustion air for condensing furnaces not only prevents adding to the negative pressure of a house, it prevents contaminated indoor air from being exposed to the heat and condensate of the furnace, greatly reducing ignition issues and corrosion factors.

    The tighter houses are made, the worst it becomes to allow the house to go negative pressure. Bathroom and kitchen exhaust fans, clothes dryers, central vacuum systems, radon mitigation systems, high hat lighting in the ceiling under an attic space, fireplace/stove chimneys and even attic access panels all contribute to negative pressure issues in houses. Outside air is going to come into the house one way or another; why not control and condition it?
    I know! I'm preaching to the choir. I just hope some of the others in the congregation learn more about what we do and why we do it just from our conversation.
    Quote Originally Posted by Hvac talker View Post
    Very good point.

    So many times I see furnaces installed with only the combustion exhaust pipe connected and drawing combustion air from inside the house. That will slightly depressurize the house and potentially bring air from the outside through cracks and crevices where in winter time the humid warm air meets a cold surface and bingo - condensation occurs which can lead to mold formation.

    Don't be lazy and install the second make up air pipe to make it a truly direct vented appliance. Your customer will thank you in the long run.
    Training is important!
    Practical Training is a must!

  2. #15
    Join Date
    May 2019
    Posts
    17
    Post Likes
    Quote Originally Posted by RoBoTeq View Post
    Outside combustion air for condensing furnaces not only prevents adding to the negative pressure of a house, it prevents contaminated indoor air from being exposed to the heat and condensate of the furnace, greatly reducing ignition issues and corrosion factors.
    So true!

    Anyone having a client which has a furnace with a single pipe installation and a flame sensor which fails more often then usually? Check if they store any household chemicals nearby, especially off gassing from laundry softeners are known culprits to cause havoc.

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