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  1. #21
    Join Date
    Dec 2009
    Posts
    12

    Default Re: Forced air furnace burner short cycling

    Installed 1.0x60 nozzle + new t-stat. Bingo, problem fixed! Also, heard from Olsen. They said I can go down to a .85x80 nozzle if I need to and change speeds at fan center (not on motor). I talked to my local hvac supply dealer. He said the ductwork is way out of balance and far from able to handle 145K btu's.

    Everyone is concluding that the primary problem is oversize furnace, undersize ducting, and my current service person.

    Now all I want to do is be have someone check so I can be 100% certain the exchanger is not damaged (that really does scare me alot)

    The new nozzle is really a patch that will get me through the winter. I'll reduct this summer.

    Thank you all for all the help. I am impressed and eternally grateful!

  2. #22
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,808

    Default Re: Forced air furnace burner short cycling

    You're high temperature sensor was working properly, shutting off gas when temp reached 240 degrees, so there should be no damage to the heat exchanger. They are generally set well below the temp that causes damage.

    Glad we could be of some help. Hope you have a warm and comfortable winter with no further problems.
    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  3. #23
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Forced air furnace burner short cycling

    Here's some run sizes, they may help,

    Rounds: inches = CFM
    4" = 50
    5" = 50-75
    6" = 75-100
    7" = 100-150
    8" = 150-200
    9" = 200-300
    10" = 300-400

    Just figure out which ones you using and add them up, the main trunk has to be sized to able to carry enough air to all the supplies. It should also be a reducing trunk to keep pressure within, every two runs and it should reduce to the next size. This will ensure that the last run on the main trunk line will get air. If you need anything else we'll be more than happy to help. Good Luck!!!

  4. #24
    Join Date
    Dec 2009
    Posts
    12

    Default Re: Forced air furnace burner short cycling

    Thank you to all!
    And to all, have a very Happy Holiday!

  5. #25
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Forced air furnace burner short cycling

    Sten ---- you might recheck those figures.
    Example-- 6 inch round = 200 cfm , 8 inch = 400 cfm
    "" an ounce of perception -- a pound of obscure "
    - Rush

  6. #26
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Forced air furnace burner short cycling


  7. #27
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Forced air furnace burner short cycling

    Sten , no offense taken.

    I have also run across that link on the internet and quite frankly didn't pay too much attention to it. I haven't bothered to read it in depth seems to me there was some mention about flex ducting. Perhaps it's a different mindset around these parts considering we concern ourselves with more so with heat and cooling is secondary. Generally we consider high volume delivery and it's not uncommon to use 6 inch rounds for 100 + cfm instead of your 75-100.

    What I posted are the volumes those ducts can handle. Perhaps I should have qualified that.

    Examples ......

    In looking at bypass zoning and with this article http://www.achrnews.com/Articles/Fea...100000f932a8c0____
    Read what volume 6 inch round ducts ratings in the case study.

    In this link to a manufacturer's bypass damper system http://www.ewccontrols.com/duct_sizing.htm note the 8 inch .
    "" an ounce of perception -- a pound of obscure "
    - Rush

  8. #28
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Forced air furnace burner short cycling

    If I read it right you're talking about a bypass, which is different than a supply

  9. #29
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Forced air furnace burner short cycling

    I have my own charts and don't use the ones on the web, I also have a Duct Catalog from FW Webb that has the sizes with the CFMs I posted. I believe Flex Duct is the same

  10. #30
    Join Date
    Aug 2007
    Location
    The Great White North
    Posts
    4,045

    Default Re: Forced air furnace burner short cycling

    Not to beat this topic to death ---- I'm talking about supplies around here are commomly used for higher volumes than you and your chart sizes work with.
    As mentioned 6 inch is in the 100 cfm and up for supplies around here.

    The only reason I mentioned and provided links for the bypass systems is I've been gathering more data on these types of systems. They illustrate the capacities are much more than your charts show.
    Whether or not they are bypass or returns or supplies is irrelavent --- the fact is they will and can be used for higher volumes than you and your charts work with.
    "" an ounce of perception -- a pound of obscure "
    - Rush

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