Replies

1. 
   The_Tennis_Court_Builder_...on_t | Oct 23, 2000 12:34am | #1

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   I would use smooth metal heat duct and oversize the run to a five inch diameter...You might want to make it accessable too...

   near the dryer stream,

   aj

1. 
   Phill_Giles | Oct 23, 2000 12:46am | #2

   *See these long runs in condo's. Some have booster fans and filters in them in them - maybe check with your HVAC hardward supplier to see what's needed. I recall someone telling me to take care in long runs to allow for expansion and contraction; and, to make sure it's well sound insulated and isolated from the framing or you can get "interesting" sound effects.

1. 
   Tim_Kline | Oct 23, 2000 05:24am | #3

   *b WBA At Your ServiceJosh, Dryer manufacturers have pretty strict rules about this. You should start by checking with the manufacturer on their limitations. I am in the process of venting a Kenmore unit with 4" rigid galvanized pipe. I don't have their specs here, but I can remember from my reading on Friday that you are way over the limit with 38' of pipe and 4 els. I have seen some people install runs like this, sometimes even with vinyl flex, and disregard the dryer manual and my pleas for fire prevention. If you must go this far, check outI have never used their dryer fans, but I can vouch for their high quality bathroom ventilation units.

1. 
   Sami_Kader | Oct 23, 2000 06:25pm | #4

   *Some info from the Uniform Mechanical Code:504.3 Domestic Dryer Vent.... shall be metal and shall have smooth interior surfaces....(except for) approved flexible duct connectors no more than 6 feet in length.504.3.2 Length Limitation. Unless otherwise permitted or reqired by the dryer manufacturer's installation instructions and approved by the building official, domestic dryer vents shall not exceed a total combined horizontal and vertical length of 14 feet, including 2 90 degree elbows. Two feet shall be deducted for each 90 degree elbow in excess of two. Seems to me that you need to have some mechanical boosting for this installation (fantech, etc) and will need to work this all out with your inspector before you buy and install everything. Fantech probably has guidelines for how long of a dryer vent run you can have when using their product. Make sure to insulate well or you will get loads of condensate as the warm moist air from the dryer cools to the attic temperature. I would slope to the outlet of the vent so that any condensate drains away and doesnt corrode the duct as much. Make sure the discharge is not somewhere where a drip would be annoying or dangerous. The fan needs to be accessible for maintenance and tied into the dryer so that it runs whenever the dryer is on. If you just install 38' of vent pipe as stated, it seems to me there is a pretty strong likelyhood of having lint build up in your 8 foot vertical run and eventually possibly cause a dryer fire. Not so good.Good luck!Sami

1. 
   David_Thomas | Oct 23, 2000 09:04pm | #5

   *Here's the table from my dryer installation manual:For a wide-angle or mini-louvered exterior vent hood:0 90's with 30' of flexible 4" duct or 48' of rigid 4" duct1 90's with 22' of flexible 4" duct or 40' of rigid 4" duct2 90's with 14' of flexible 4" duct or 32' of rigid 4" ductExtrapolating to 3 and your proposed 4 90's:3 90's with 6' of flexible 4" duct or 24' of rigid 4" duct4 90's not allowed with flex 4" duct or 16' of rigid 4" ductsubtract 10' for a low-angle exterior vent hoodSo the four 90's plus 38' of rigid 4" is well beyond recommendations for my particular, expensive, modern, GE dryer.AJ has the best idea of using 5" rigid for the 90's and straight runs. That would be same pressure drop as 26' straight of rigid 4" (or 12' straight + two 90's in rigid 4"), well within limits for any dryer. If you use 45's instead of 90's they only hurt you half as much (two 45's equals one 90). Also, if you use two 45's to offset instead of two 90's, you can shorten the length of straight pipe. Although you have to cut oblong holes through the studs or joists to accomodate the 45 angled run. -David

2. 
   Tom_Payne | Oct 24, 2000 05:48am | #6

   *I've used the fantech booster and it works great. You'd never pass inspection without one around here with a run that long. I just cleaned a 20 foot dryer run with my leaf blower and it worked great too!

3. 
   FredB | Oct 24, 2000 06:25pm | #7

   *Josh:For goodness sake, read the installation manual! Everything you need to know is in there. No manual? Talk to the store where you bought the dryer or call the manufacturer. They will give you one. Depending on the dryer you have different constraints.

4. 
   Andy_Engel_ | Oct 25, 2000 07:25pm | #8

   *My dryer vent isn't that convoluted, but it's all of 20 ft. I used a Fantech booster and it's wonderful. The clothes actually dry in about two thirds of the time they took in our old house, where the same dryer vented straight out the wall. Andy

5. 
   Brian_Gale | Oct 25, 2000 08:41pm | #9

   *Josh-Regardless of all the posted info and codes here...call the dryer manufacturer's customer service if you can. I had the same issue (wanted to relocate the unit) so I called Whirpool's customer service (found on internet) with my model number, and they faxed me the info on my dryer from their electronic database. And if you should have a problem in the future with the length/routing/ducting/number of turns you did according to the fax that THEY sent you some recourse may be possible...Also, Whirlpool was extremely helpful, polite, and I had my info within the hour...Good luck!-Brian

6. 
   FredB | Oct 27, 2000 06:42pm | #10

   *Brian:Glad to see your post. At last there is someone else here who sees the wisdom of getting info from the manufacturer.I always wonder about the mind set of someone who posts here about a simple question that is best answered by the people who built the thing in the first place.

2. 
   josh | Oct 27, 2000 06:42pm | #11

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   maybe I missed something in the books. is there a maximum length and number of turns for dryer vents. We are being asked to relocate a dryer and its vent (due to a remodel) and it will have to have 1-90 go up 8 feet and then a combination of 3 more 90,s and about 30 feet of run before it gets out of the house,there will be no more rise.All the 90's will be sweeps . Do we have to have any kind of slope or clean outs enroute? dryer is electric.