Flue pipe quesions

[Frosty28]

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.

[gravity]

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.

[matt1124]

The the increase to 3"?

[philjafo]

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.

[syndicated]

Your 2x3" increaser should be as close to the furnace as possible.

[Coloradotech]

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.

[rundawg]

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.

[Coloradotech]

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!

[gravity]

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.

[barriefurnacerepair]

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?

[Frosty28]

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?

[gravity]

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.

[wahoo]

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??