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  1. #1
    Join Date
    Oct 2012
    Location
    Central IL
    Posts
    18

    Flue pipe quesions

    We did a install of a 100000btu 96% goodman/amana furnace recently and the flue pipe configuration was a little different in my opinion.

    We put a 2" 90 on pointing to the left, it continued 3' and turned up where it was increased to 3" for 2' and made another 90 turn to get out of the house appr 5' horizontal. immediately outside the house we placed a 45 pointing down and glued a reducer on to decrease it back to 2" .

    All of this had good fall, but my question is what are the benefits or problems that could come from this setup if any. Is this something to be concerned about, the flue gasses are condensing as they should be and its not trapping water. Just trying to learn right from wrong.

  2. #2
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,379
    follow the venting tables in the book that came with the furnace. The only way you would know there are problems is to perform combustion test.

  3. #3
    Join Date
    May 2011
    Location
    Oklahoma
    Posts
    361
    The the increase to 3"?

  4. #4
    Join Date
    Aug 2012
    Location
    NE wisconsin
    Posts
    392
    As stated read the book that came with it, it will tell you the correct size for the vent pipes.

    I have seen vents setup similar to what your describing, but they reduced from 3 to 2 to go through the wall because the installers either were to lazy or didn't have a drill to go to 3. That furnace produced high levels of CO.

  5. #5
    Join Date
    Feb 2010
    Location
    Calgary, Alberta
    Posts
    1,010
    Your 2x3" increaser should be as close to the furnace as possible.

  6. #6
    Join Date
    Nov 2012
    Location
    Loveland
    Posts
    18
    Quote Originally Posted by Frosty28 View Post
    We did a install of a 100000btu 96% goodman/amana furnace recently and the flue pipe configuration was a little different in my opinion.

    We put a 2" 90 on pointing to the left, it continued 3' and turned up where it was increased to 3" for 2' and made another 90 turn to get out of the house appr 5' horizontal. immediately outside the house we placed a 45 pointing down and glued a reducer on to decrease it back to 2" .
    All of this had good fall, but my question is what are the benefits or problems that could come from this setup if any. Is this something to be concerned about, the flue gasses are condensing as they should be and its not trapping water. Just trying to learn right from wrong.
    From were the 2" 90 goes to 3" off the furnace will trap water and make your pressures wrong in the flue pipe and cause Flood back. Were you 45 down outside and reducer to 2" (?) snow level problem, ice build up that just sounds all wrong. As said read the venting tables in the installation book.

  7. #7
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,015
    Quote Originally Posted by Coloradotech View Post
    From were the 2" 90 goes to 3" off the furnace will trap water and make your pressures wrong in the flue pipe and cause Flood back.
    If you re-read his thread, it sounds like he turns vertical before increasing to 3".

    Vertical transitons are OK, and will not trap water.
    Instead of learning the tricks of the trade, learn the trade.

  8. #8
    Join Date
    Nov 2012
    Location
    Loveland
    Posts
    18
    Quote Originally Posted by rundawg View Post
    If you re-read his thread, it sounds like he turns vertical before increasing to 3".

    Vertical transitons are OK, and will not trap water.
    you are right I was seeing in my head 3" not 3' on the next part and not reading the rest of it. my bad!

  9. #9
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,379
    Reducers should only be used in the vertical position. At the outside of the house, I like to use a tee on the exhaust. On longer runs, at about 30' I like to start pitching my pipe back down hill.

  10. #10
    Join Date
    Nov 2012
    Location
    Barrie, ON
    Posts
    29
    I can only guess at the model# but they do have a 95% 100,000 BTUH unit that is approved for 2" which is a bit of a surprise. Boosting the size to 3" will reduce the air velocity in that section and the additional reducer at the end will cause a slight backpressure like you'd see in a two-stroke motorcycle. Did a motorcycle mechanic install this one?

  11. #11
    Join Date
    Oct 2012
    Location
    Central IL
    Posts
    18
    Thanks for the replies this site has become almost invaluable (and addicting too ) I asked because I was taught at tech school to increase the size as close to the furnace as possible. I wanted to look at the manual but somehow they disappear before I can see them.

    The increase was done on a vertical run, but the decrease at the termination is what had me curious how it would effect airflow. The comparison to the minbike is a good one I was thinking it would cause a venturi effect, which I think is similar.

    gravity.....
    Use a tee?? Do you position that vertically I assume. Whats the purpose of the tee?

  12. #12
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,379
    If it rains the water falls thru the tee. It's a little harder for kids to throw rocks in the pipe if it's a tee. The list can go on. Yea, the tee goes vertical. I guess it wouldn't hurt if it was horizontal, I've never tried it.

  13. #13
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,315
    I'm pretty sure the code requires that the manual is kept with the furnace. Why or how is the manual disappearing before you can take a look at it?? Are gremlins stealing it, or is the system installed by inept morons??? Okay, I appologise for any blunt remarks, just sounds like someone is not paying attention to detail here??

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