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Question DetailsAsked on 3/3/2016

Dryer venting options

The old vent was run down about 2' then over 15' back up a foot then out to the outside. This way caused the dryer to take longer than normal to dry and I believe for the dryer to fail prematurely. Every thing that I have found tells me I should run the vent up first. But my only option there would be to go up 8' then back towards the front of the dryer out to my back porch and through the roof. I have also seen some thing advise going back towards the dryer and through the roof. Any thoughts on that or should I stuck with the original route?

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2 Answers


You would have to check on the installation instructions in the manual for your dryer, but generally they can handle at least the code maximum - 25' total run of 4" metal duct plus up to an 8 foot transition duct, except that 90's count as 5 feet and 45's as 2.5 feet each. Also, if the manufacturer info says it can handle a longer duct, that controls - some are rate4d to over 100 feet of duct.

So, in your case you had probably two 90's at the dryer - one at the dryer down into the floor, one 2 feet down to horizontal - then 15' run, then a 90, up a foot, then another 90 to outside - plus a hood or louver which runs from 2-5 feet of loss, plus any transition duct from dryer to first 90. SO, in your case looks like 37-40 feet of "duct equivalent length"- (4 90's, 15' duct, hood) - plus any transition duct. Most dryers would handle this total, though some would not. In extreme cases it is possible to put a booster fan in-line, but they should be avoided where possible because they are one more thing to fail, and can also block with lint clumps that break free and move along the line as one large clump.

You want to go the shortest distance (equivalent length) and minimize 90's as much as possible - but actually going up is worse than down - you want to minimize "up" runs as much as possible because that is where lint accumulation builds up. The ideal is down into the floor, then horizontal to the outside.

I would have a Heating and A/C contractor come look at it and give you his recommendation - and I would stay with an in-floor or in-ceiling route if feasible - not all the way to the roof, both because of the lint buildup along the way, but also the attic section would have to be well insulated to prevent condensation buildup which can cause clogging of the lint, plus you geat unsighly and growth-causing lint deposits on the roof.

Couple of other thoughts - if your duct was corrugated tubing type, that is much higher friction and has been known to cause problems with friction and with kinking (and not being fire resistant) - if that is what you have (no longer legal) you should replace it with rigid metal duct if at all possible. Ditto to your transition duct - many times you can eliminate the flex tubing at the dryer and put in hard ducting all the way, tying it down at the floor and shimmed up so it is just the right location to push the dryer up against to hook up after the dryer has been pulled out for maintenance.

Also - you go up a foot then out - is it feasible to change that to straight out, eliminating probably 2 90's and a foot of duct ? That would cut 11 equivalent feet of duct PLUS get rid of the accumulation point for lint that failed to make it the foot up to the exit.

On the dryer failure - basically, unless the dryer duct was plugging up partly with lint, uyour length ducting would not have contributed to failure.

Cost depends on your run direction of course, but $250-600 is a common range, from simple through-joist run to through attic to roof or outside vent - general range.

Answered 4 years ago by LCD


Horizontal metal runs, with as few 90's, as possible is the best. You will still need to clean the dryer duct annually and clean the area in back of the dryer behind the vent connection. I lost a dryer due to clogging in the back of the dryer because I did not know there was a cover I could remove and clean that area. In your case I would consider moving the dryer to a better location.

Source: Poppy Ross

Answered 4 years ago by PoppyRoss

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