# Does a dryer vent need to be insulated?



## cbzdel (May 11, 2010)

I installed a 4" rigid dryer duct running under my house in the crawlspace and then vented to the outside. Should it be insulated? I replaced ductwork that went vertical into the attic and out the roof which was not very efficient, but I can say it was insulated where it ran though the attic space.

Thanks in advance!


----------



## SeniorSitizen (Sep 10, 2012)

cbzdel said:


> I installed a 4" rigid dryer duct running under my house in the crawlspace and then vented to the outside. Should it be insulated? I replaced ductwork that went vertical into the attic and out the roof which was not very efficient, but I can say it was insulated where it ran though the attic space.
> 
> Thanks in advance!


I suspect the insulation in the attic duct was installed to aid in the prevention of condensation within the pipe during colder weather.

Whether your crawlspace duct needs insulation depends some on whether the pipe will drain condensation water to the outside. Keep in mind the dew point temperature of the exhaust air within the pipe constantly changes as the clothes dry, with the DP temperature being very high at the beginning of the cycle and much lower at the cycle's end. 

Insulation will allow the pipe to raise and maintain a temperature above dew point sooner in cold weather therefore allowing the duct interior to be dried at an earlier point in the cycle, so yes if it were mine, I would insulate.


----------



## jogr (Jul 24, 2007)

It's not required by code in my area but your local code may be different. Yours was probably insulated in the attic because the moist exhaust may have been condensing and dripping back down the duct in the winter when the attic was cold. 

If your crawlspace is cold in the winter you might get similar condensation but if you slope the duct to the vent it shouldn't accumulate. If it's level or sloped slightly upward then condensation might accumulate in the duct.


----------



## cbzdel (May 11, 2010)

What would be best to insulate it with? In my attic, it was just insulated with fiberglass insulation wrapped around it, is that the best, or is there something better available for dryer use?


----------



## Ron6519 (Mar 28, 2007)

They sell insulated tubes that will sleeve over various sized ducts. Big box stores sell them as well as HVAC and plumbing supply stores.


----------



## user_12345a (Nov 23, 2014)

If the crawlspace is not heated and below room temperature, you should insulate the pipe to prevent condensation.


----------



## cbzdel (May 11, 2010)

I went to both of the big box stores in my area, and both have never heard of anything called an insulation sleeve. They showed me pre-insulated flexiable ductwork for like bathroom exhaust vents but nothing that could be used for ridgid ductwork. Both stores recommended I purchase just a typical fiberglass insulation and wrap the pipe.

Does anyone have a good link for a 4" duct sleeve that I could order online?


----------

