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This is my setup, 1986 built town home. I just purchased a dryer and before connecting it, I decided to inspect the 4" tube going from the dryer, up behind the wall to the crawl space / attic and out of a hole cut from the roof.

dryer setup

This is what I found:

enter image description here

That's just a 12" segment, I kept, it was like this for 12 feet. While I assume, total blockage is bad, I presume that so is even this amount of lint stuck to wall of the tube. (Is that right or did I remove it for nothing?)

Anyhow, they had a aluminum flex duct tube tube going through the wall, but I'm wondering if perhaps it would not be best to replace it with a rigid smooth (without the flex ducting) aluminum tube for the straight section that goes from the bottom the wall behind the dryer into the crawl space. Then at both ends, replace it with new, clean flex duct tubes.

I'm also thinking of adding a secondary lint filter so this doesn't happen again.

Any advice, or what to use is appreciated, I want the safest solution.

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    Depending on where you live, and what building codes are adopted in your area. Rigid duct may be the only code compliant material (International Residential Code (IRC), International Building Code (IBC), International Fuel Gas Code (IFGC)). See this answer for code verbiage.
    – Tester101
    Mar 25 '14 at 14:24
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If possible, you want everything rigid: the connection from the dryer to the wall, the duct in the wall, and the duct in the attic. Sometimes rigid for the connection between the dryer and the wall is difficult to get right with a rigid duct so if you have to go with flexible duct then use the smallest piece practical.

A secondary lint trap is probably not worth the effort. instead, invest you money in a dryer vent cleaning kit, which is a brush with a couple of screw-together flexible rods that you can chuck in to a drill. Clean your duct using this brush once a year.

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    Believe in the power of elbows - the stock rigid vent elbow can be rotated to adjust to angles different than the one it comes home from the store in, so you can get whatever angle you need (so you can adjust a pair to allow you to have a straight run from the ceiling hole to the roof hole, for instance). Also - pay attention to the direction of the joints, and seal them. And if you are in a cold climate, you may want to insulate the duct in the attic to reduce frost build-up.
    – Ecnerwal
    Mar 24 '14 at 20:30
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    If you have to use flexible duct at all, use 2' or less semi-rigid metal duct. The inside wall of the semi-rigid duct is fairly smooth, and will not collect lint as a flexible duct would. The semi-rigid duct is also metal and so will resist burning, unlike flexible duct.
    – Tester101
    Mar 25 '14 at 14:20
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Longneck is right on the rigid venting. This is a must going straight up like this. Also for the issues that you have had it is common sense to put a vent booster on the line. I think the rigid vent will certainly help but if you had that many problems then I would assume that gravity is getting the best of your situation.

If you just replace with rigid venting then you will basically have the same issues but it will fall further down (maybe easier to clean). I have installed the one in the picture a couple of times. I basically turn dryer on and see what kind of force the vent has on the outside. I would guess even after getting cleaned and changed to rigid yours would have very little.

enter image description here

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  • He didn't mention any issues with the dryer functioning - he just inspected the duct and found it covered in lint (which is utterly normal for flex, and one of several reasons not to use flex.) Given that rigid flows air easily a couple of times better than flex (I found some nice research from Texas to support an HVAC answer within the past couple of months) I see no reason to jump on a $176 dryer booster because lint is clinging to flex duct. Only down to 6" but pretty clear: mmmfg.com/pdfs/060601_CC-KW_DuctTechPaper.pdf
    – Ecnerwal
    Mar 24 '14 at 23:47

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