Replies

1. 
   Scott | Aug 12, 2010 10:42am | #1

   I don't think eighteen feet of ducting should be a problem. Your appliance docs should tell you the recommended limit and number of elbows that are allowed.

   More importantly, is the ducting all made of metal with all joints taped with foil tape? Where is the lint buildup that you describe?

   If you are absolutely set on adding a booster fan, Fantech makes one, for a couple of hundred bucks.

2. 
   rdesigns | Aug 12, 2010 11:13am | #2

   As Scott says, 18' with maybe two 90-degree bends should not present any problem to any faily new dryer--most will allow much more than that.

   Are you cleaning the lint filter regularly? Is the existing duct made of smooth metal or is it of some corrugated material that creates extra friction?

   A booster fan needs to be interlocked with the dryer so that it runs any time the dryer runs, and it must be accessible for maintenance and inspection. Also, if the booster fan fails, it becomes a major restriction in the dryer duct that you might not know about, and which would cause a lint buildup with possible fire hazard. A booster fan should be your last resort.

3. 
   JTC1 | Aug 12, 2010 01:51pm | #3

   18' should not be a problem, unless as others have said, you are not running in smooth metal pipe.

   My rental house has a dryer which is several years old, the instructions say 70' maximum run in 4" rigid pipe.

   70'! you say......... here comes the "but" - there are "conversion" figures in the installation instructions like a 90 elbow = 15', etc. so 4 elbows and 10' of straight pipe is the maximum - you get the idea. Check your instruction / installation manual.

   I have had the best luck using the 4" rigid aluminum pipe, no screws anywhere, foil tape at all joints including the longitudinal  "snap together" pipe seams. The less air you leak, the more velocity you get.

   Jim

4. 
   Clewless1 | Aug 12, 2010 08:21pm | #4

   No worries ... MAKE SURE it is NOT flex duct. If it is, toss it and replace it w/ rigid ... at least until the last couple feet.

   Just say no to flex duct.

5. 
   billg71 | Aug 12, 2010 10:16pm | #5

   IIRC(and that's chancy these days)...

    I seem to remember that each 90 is the equivalent of 5' of duct run and you're limited to 35' of run by code. So it looks like you're at 28' more or less, plus allowance for a short length of flex which should still get you past the inspector. You said lint built up in the house, do you mean the duct or the house proper?

   The existing 18' equivalent run doesn't seem enough to me to cause problems. If lint's accumulating in the house as it is you've got a sealing or appliance  problem, not a duct problem(assuming the duct was installed right). If it's building up in the duct and the duct is hard pipe properly installed and sealed, it sounds like the dryer just isn't pushing enough air. Maybe your customer needs to clean his lint trap more often or buy a new dryer....

   I agree with the other replies, avoid flex duct for a dryer at all costs!

   HTH,

   Bill

6. 
   user-7660861 | Aug 15, 2010 11:00am | #6

   Dryer Vent

   I have a similar situation and about a 22' run with 2 90's.  Lint build-up was bad, then added an in-line fan from Fantech.  Just need to get power to it as the "interlock" is a pressure differential switch that turns on the fan when the dryer starts up.  It runs on 10 min. cycles and once dryer shuts off, it just runs until the cycle ends.  It works great and is very quiet.  Had it for about 8 yrs, cleaned it twice in that time.  Fantech DBF 110.

   John