How to increase volume flow through 3 inch PVC pipe?

richard904August 7, 2007

I have a contemporary house. The laundry room is at the lower level, and the original owner put in a 3 inch PVC pipe to vent the dryer. There are concrete walls on one side of the laundry room and finished rooms on the other sides. There must be a way to increase the volume flow through the PVC pipe to properly accomodate a modern dryer. It would be big money to re-vent using a proper 4 inch metal duct, and unless by some miracle I could find a real pro I just think there could be a real mess. Ducting experts must have some ideas on this. The Laundry Room forum here does not look at these type of problems, and there were no practical suggestions. Why can someone not just build a box with a blower and filter and use this to enhance the volume flow?

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why do you need to increase the volume flow?

As long as your existing PVC pipe can handle the current dryer output you are fine.

    Bookmark   August 7, 2007 at 6:56PM
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The clothes dryer manufacturers have specifications on the duct work. They want ducting not to exceed a certain length, and they want 4 inch rigid metal ducts. A 4 inch duct has twice the flow capacity of a 3 inch duct. The restriction of a 3 inch duct causes the clothes to take much longer to dry and also stress the fan motor. PVC pipe is known to build up a static charge which causes lint to stick to the surface - thus requiring more frequent cleaning to avoid a possible fire hazard.

For long 4 inch metal ducts there are dryer booster fans. The radon people have fans that go into 3 inch PVC pipes that run continuously.

What I need is something that will essentially double the flow capacity of the 3 inch PVC pipe while the dryer is running. It can sense the dryer fan pressure or whatever and just ram flow through the pipe and be done at reasonable cost. I just cannot believe that duct manufacturers cannot design and custom build devices like this.

    Bookmark   August 7, 2007 at 11:04PM
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"powered dryer vent"

Yahoo or Google this and see what you get. I got 5 hits at the top of the page.

    Bookmark   August 8, 2007 at 7:45AM
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3" PVC was a poor choice for drier venting material. Most manufactures spec. 4" metal with taped joints 15' maximum with 1-elbow. You have what is you have and it is not good. FANTEC produces a drier booster fan for long drier vent runs. This fan is pressure activated and simple to install. I would suggest you call FANTEC, talk to one of their engineers about your problem. Possibly they can help you or make a recommendation. The drier booster fan retails for about $200.00 here on the east coast. Check with GRANGER, they carry Fantec products as well as your local electrical supply house.

Good luck.

    Bookmark   August 8, 2007 at 9:56AM
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I e-mailed FanTech Technical Support, and to their credit, they answered right away. Their booster fan is designed for 4 inch metal ducts. They feel that a 3 inch PVC pipe is too restrictive, and will not recommend their booster fan for my application. However, in this whole world, there must be some engineer who can spec out a solution that will pump enough air through the PVC to exhaust the dryer properly. This would be safer and cheaper than someone tearing up half my house to install the proper duct work. I will not comment about contractors who would use 3 inch PVC to exhaust a dryer.

    Bookmark   August 9, 2007 at 1:06PM
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I suspect they spec 4 inch ducts to cover most contingencies - Long runs, elbows, changes of direction and the use of flexible ducting which has lots of non-straight sections

To get the most from a 3 inch duct, elininate all of those 'issues' - Shortest possible run, as straight as possible and eliminate all elbows or changes of direction

If you have a 3 inch hole in the wall and you could position your dryer immediately in front of it with a straight run only a foot or two long with no bends or elbows, I'll bet it would vent just fine

A 2 foot section of 3 inch vent pipe would flow more air than a 10 or 15 foot flexible 4 inch line full of bends and elbows


    Bookmark   August 9, 2007 at 3:52PM
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Sounds like you are trying to get 16 ozs. of water in an 8 oz. glass. It's not going to happen.

Do it right or don't bother doing it at all.

    Bookmark   August 12, 2007 at 8:56AM
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I think someone brought up using a condenser dryer on the laundry room forum. I think that would be the best fix in your situation. Why would you want to spend a lot of money on possibly unsafe fixes if you can just stop worrying about that pipe alltogether. A condenser dryer is made for laundry rooms that don't have a (proper) vent. They are not as efficient as vented dryers, but then all your other fixes might be worse than that...and more expensive.

    Bookmark   August 13, 2007 at 8:40AM
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