# Exterior Ductwork for a Dryer vent



## NailedIt (Jun 19, 2009)

I was just talking with my local building official about needing 12" above the "accumulated snow depth" requirement for venting. Adding turns to your vent reduces the efficiency of the vent. I wrestled with this issue in trying to get my new dryer location to vent at the back of the house, as opposed to next to the front entry. Each 90deg turn reduces the length of the vent run you can have by 5', so generally I would think yes you ought to be able to do that, though I've never seen anything like that outside in plain sight.


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## lappin_jeff (Sep 22, 2009)

Thanks for the reply! Do you think it would be safe to use pvc for the exterior portion and standard metal 4" duct work for the interior?


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## Jacques (Jul 9, 2008)

most people use the flush mount hood with the 4 flappers-this then vents straight out instead of down.


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## lappin_jeff (Sep 22, 2009)

...I wouldn't be able to get the bottom of the vent more than 4" from the ground. Is there some way I could use a couple of elbows to get me the 12" from the ground clearance...

I cant flush mount to the house because of clearance problems. That's why I need the elbows. What my question boils down to is, Can I use PVC to do it? It would only be on the outside portion, the rest of the run would be standard 4" metal. Would there be condensation issues? Would I have to include a drain of some sort? Is there some type of Z-Flex (tankless water heater type duct) that would work better?


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## Jacques (Jul 9, 2008)

you need a dryer hood on the outside of the house-regardless if it's 4"" or 4'. if nothing [adding mulch,snow,etc] will reach the 4" mark and your local code allows that clearance, use the flapper style. why mix the pvc with the metal? just use the dryer metal ducting all the way. the pvc to the outside won't allow you to put a hood on it[not sized for that]...how longs the entire run?? look up your dryer and see max length recommended [5']each 90*..you could come out of the house and then go up the wall put a 90* on it and then the hood--this will look terrible but you could do it.


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## Gary in WA (Mar 11, 2009)

Ask your local B.D. as the code says "DUCT TERMINATION *End outside* in back-draft damper and no screws (1501.1 2437.3)
You may want to ask them on this, end outside- *not continue outside then end outside*..... The condensation would be tremendous and instant for moist heated air with fabric particles cooling off from the long run out anyway, hitting air that would be over 100 degrees different... then to hit an 90* elbow, short pipe and another elbow. I cleaned one that had 2 els and 30' of pipe, had a 1-1/2" hole for air after 20 years use. Read the specific brand ducting recommendations also, they vary greatly: http://www.appliance411.com/faq/dryer-vent-length.shtml
Be safe, Gary


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## NailedIt (Jun 19, 2009)

Would an insulated chase built around the duct solve the condensation issue? If the length of duct, # of turns, clearance, and aesthetics align, etc... The one I just replaced was previously, ahem... vented into the crawlspace for 30 years via a pvc pipe. The pipe had popped off inside the wall so the lint was expelled, along with the moist air, into the wall cavities, ceiling, and crawlspace. Fortunately there aren't any rotted joists or mold issues. I have a 27' run with 2 bends via 4" steel duct with a louvered cover.


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## Gary in WA (Mar 11, 2009)

The latest code specifies* smooth metal inside* 1501.1 Flex duct (maximum 8') can only be used inside at the dryer with no concealed flex connectors (must be metal). NO screws in airflow. *25' maximum duct run* minus for elbows. Male ends of duct must face direction of airflow. Longer length OK if manufacturer instructions permit. 4" minimum ducting. End outside in backdraft damper &* no screens*. *Booster fans no longer* accepted. Longer radius 45* and 90* as per ASHRAE accepted. 
I would ask your B.D. about a chase as a lot of people may have a similar situation. The newer houses are putting the laundry room back on an outside wall, where they used to always be. 

Be safe, Gary


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## lappin_jeff (Sep 22, 2009)

Thanks For all the great posts! Haven't sorted what exactly I'm going to do yet but you have definitely given me a lot of great info.


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