• We have to vent our dryer outside and we will NOT be using any form of flex pipe.
  • The whole thing will be vented with rigid 4" aluminum vent pipe.
  • It is going to take a total 18' of pipe and one 90 degree elbow in order to make it an exterior wall. We have chosen to go to a wall versus out the roof top since we don't want to mess with installing a vent box on the roof. It would also create unnecessary angles that we would rather avoid, and even though the exterior wall is further away, there is no elevation change, etc.
  • Including a diagram to show what I'm talking about...

As long as I connect the pipe sections correctly (with the crimped ends pointing away from my flow source) does it matter how many seams I have? Problem is, I can only get ahold of 5' sections of pipe. No one seems to carry anything longer, even places like Ferguson, etc.


  • I am under the impression as long as I am under 25' I should be fine.
  • I am also assuming that the 90 degree elbow "counts" as 5', so my total run is around 23'.
  • Since the dryer was originally vented into this attic/crawl space about 30 years ago, anything is better than the current set up!

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  • 1
    The manufacturer's documentation should specify the maximum developed length of the pipe, as well as how much to add for each elbow. As for the seams... As long as they're sealed, and don't reduce the area of the vent, there should be no problem.
    – Tester101
    Commented Oct 24, 2016 at 23:21
  • 1
    Make sure the seams don't add lots of drag. Major counter-example: using screws that protrude into the airstream. Commented Oct 25, 2016 at 1:46

2 Answers 2


The number of seams is really not the issue. The length is, but this is probably a better solution than alternatives.

When you put the pieces together, you should arrange that the downstream sections fit over the upstream, so the interior transition doesn't have an edge that lint catches on.

Another subtle thing, would be to try to put a slope down from the elbow to the exit, so any condensation runs out. Avoid any dips. I put aluminum tape on mine to seal the joints and keep it together.


Seems don't matter and in your case i think you are doing your vent with the right material. In your case if you are able to get to them annually to take apart and wash them it helps with saving on electric bill as the dryer becomes more efficient when the venting is clean! Also faster drying time, if you have that soccer mom that needs to stay on schedule!

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