I recently had a Lennox A/C and furnace installed. The condensate line drips water into the basement floor drain, as my old one did. But now there's also a little side vent in the line that is also dripping a considerable amount of water, and this side vent just drips the water right onto the floor, causing those wet spots that you see in the photo. It doesn't seem normal. Why would there be one vent that goes into the floor drain and another that just drips it right out onto the floor?

furnace photo with condensate line

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    It's an overflow drain. If (when) your drain line gets clogged, it will flow out of that hole instead. Put a little bleach in the line and try to get it cleaned out Commented Jul 27, 2023 at 3:05
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    Is the pipe glued into the tee? If not, I would rotate the elbow so the end of the overflow is slightly elevated. If it were glued, I would either cut off the elbow and replace it, or just add a 45 degree elbow to the end of the existing pipe.
    – spuck
    Commented Jul 27, 2023 at 15:26
  • Tried to rotate the pipe but it feels glued in. Probably will have to add an elbow of some kind. Commented Jul 27, 2023 at 17:52
  • I'm curious for the HVAC experts here; is this the typical way to do it these days? I've never seen an overflow like this, but my sample size is low. I'm curious about the height of that overflow; it's assuming any clog would form below the tee.
    – spuck
    Commented Jul 27, 2023 at 21:47

2 Answers 2


You have a new AC system. It's making cold air. It also is making the condensation it produces cold, which in turn creates more condensation in the drip line itself.

Simple fix. Add a series of 90 deg. elbows to the end of the overflow stub. (as shown in blue)

This will make any condensate flow back down the discharge line and being farther distanced from the main line it will not produce as much condensate. A little insulation will help too.

In the event that a large amount of water starts dripping from the overflow stub, you know there is a clog. That will have to be addressed.

enter image description here

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    Just a single upward bend, even a gentle one, should be enough to keep normal condensation flowing out of the main drain below. It sounds like this stub is level it tilted downward, causing the problem.
    – keshlam
    Commented Jul 27, 2023 at 13:19
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    @ keshlam, I thought of just an upward elbow. You are right it would probably take care of the problem. However, I was weary of something falling into it. I know not likely, but my experience is, if I drop something it falls into the one small space that you don't want it to go.
    – RMDman
    Commented Jul 27, 2023 at 16:59
  • Valid. Pick your own overkill. Personally I'd just have canted that side stub upward a bit and called it good.
    – keshlam
    Commented Jul 27, 2023 at 19:24
  • @keshlam I attached a 45 deg. elbow with a few extra inches of pipe. Commented Jul 28, 2023 at 20:18

As mentioned, it's an emergency overflow. There's probably an incidental amount of condensate that comes out just from dripping down the downspout—no good way to force it away from that side of the downspout. One way to eliminate the output from there but still retain the emergency operation would be to install a P-trap. I like the clear type, like this: https://rectorseal.com/ez-trap-group/ Easy to see if there's sludge in the trap, and easy to flush. This particular one has a float switch that tells you if it's backed up, but you can get them without the switch.

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