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I'm replacing a gas dryer in a condo that previously had 2 plastic flex pipes and a 5ft aluminum rigid duct.

I planned to replace it with rigid steel. I got most of it dry-fitted correctly, except the end of the run. There's about 2 feet between my new run and the exterior vent. See side-view image below (note: the picture does not show that the exterior vent is a little lower and also to the right):

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The end of the run is in a tight area, in a small 3x3 closet that also contains a circuit breaker. To get through here with rigid steel ducts, I'll need several elbows and short extenders. I'd rather use a bit of semi-rigid flex vent in a small C-shape instead, for ease of installation and less seams.

The red dashed line in my picture represents where the flex duct would go. It would be about 2 to 2.5 feet long.

  1. Is it OK to use flex duct near the end of a run at this length (about 18 ft total)?

  2. (More generally) If a duct is going to require several quick bends and seams in a tight area, is it ever better to use a single flexible duct instead? If yes, how should that determination be made?

Edit: I ended up admitting to myself that I was trying to be lazy and fanangled a few adjustable elbows to cover this gap. I'd still like to know the answer to #2.

  • How high up on the wall is the vent terminus? – ThreePhaseEel Apr 4 '18 at 22:51
  • About 6'9". My run is going between 2 joists; the terminal vent is just under the joints – Scribblemacher Apr 4 '18 at 23:09
  • Is the vent exiting directly above or to the left of the circuit breaker? – mikes Apr 5 '18 at 0:02
  • The vent is beside it, to the right. It's going out a window at that location (the glass was replaced with sheet metal) – Scribblemacher Apr 5 '18 at 11:04
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The drier installation instructions should typically have venting parameters that should be followed. That being said, rigid duct will always flow more air than corrugated flexible aluminum tubing. 4” aluminum flexible tubing flows approximately the same air as 3” hard pipe. All of the little ridges slow down air flow significantly. While a few feet of flexible tubing will probably not drastically reduce air flow I would always avoid it if at all possible. The less resistance the faster your cloths will dry.

  • The instructions said "rigid only" and provided maximum lengths and elbows (I think most/all gas dryers tell you not to use flex duct though because of CO). Your 4" rigid to 3" flex "conversion" is helpful for understanding what using flex in this case would do to the run. – Scribblemacher Apr 6 '18 at 13:02

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