I live in Houston, TX (Very Hot, Very Humid). In the summertime, my dryer is dripping with water, when not in use. I do not have overly excessive drying times.

My dryer is vented via an unfortunate run of over 25 feet with two elbows. It exhausts through the roof. Dryer is in the center of the first floor, so the vent goes up to the second floor, runs through the ceiling/floor, comes out in an attic and through the roof. The attic is unfinished, with temps well over 120F on an average summer day in Houston.

My guess is that I have hot moist air pouring down my dryer duct, hitting my nice cool air conditioned dryer and condensating.

Initial google searches have pointed me at the Fantech DBF110 which is a booster fan that you install on your duct run. I'm not certain this is going to solve my problem, as it doesn't run constantly, only when the dryer is running.

Would I get more bang for my buck by insulating the duct and trying to seal it up? Any recommendations on materials if that's the case (thermal blanket, just wrap fiberglass, other)?


As Eric suspected, I didn't have a working flap on my dryer vent. So I bought one and gave it a test run and I wasn't happy with how little the flap opened from the pressure on the dryer. So, I installed the booster fan as suggested by Doresoom as well. We had a few hot humid days after that, dryer stayed dry. My clothes drying times are pretty low too, 30-45 mins.



Fan pic is before I cleaned up the electrical, looks a little neater now. The ideal install for that fan is with the bracket on a stud, unfortunately there was no good way to attach a stud and avoid cutting a new hole in the roof. Luckily the fan is pretty light.

  • I'm confused. You're dryer is on the first floor and the vent goes up and then through a crawl space? Do you mean an attic space?
    – aphoria
    Aug 11, 2010 at 19:03
  • Yes, sorry. I have an attic over my second story that I call the attic and a little overhang (from the roof pitch) that's on the second story that I have to crawl into. Nothing under the house :) Aug 11, 2010 at 20:10

3 Answers 3


Usually a dryer vent will have a spring loaded flap where it exits the house to prevent outside air (and bugs, rodents, etc) from coming in through the pipe. If you are getting airflow from outside through your vent pipe, it sounds like either you don't have one or it isn't closing. I would check that first.

  • +1 It's very likely that this isn't closing correctly. Sometimes wasps like to build nests in this sheltered spot.
    – Rob Napier
    Aug 12, 2010 at 16:49
  • Got on the roof last night. No flap at all, just a birdhouse looking thing to keep the rain out. I'm ordering one of these and hopefully my roofing skills are up to snuff. bathroomfanexperts.com/product.php?product=174479 Aug 12, 2010 at 18:13
  • My problem is the same but the situation is just the opposite, I have a very short (less than 12" 30cm run and there flap (plastic) is closing. Any ideas? Or should I make this a question of its own?
    – Duston
    Aug 21, 2021 at 13:30

Depending on the type of duct you have, 25 feet and two elbows may be near or over the length limit for dryer vents without a booster fan. This website lists the limits.

  • Thanks, I'll probably do that next, I'm sure the family won't complain if clothes dry faster. Aug 12, 2010 at 18:14

I have seen this when the inside was kept cold by the AC, the moist air from outside would condense in the vent and come into the dryer. The dryer vent trap door would not seal completely. It is possible you have rain coming in,past the dryer vent trap door (if there is one). I would suggest having the builder move the vent low and out the wall instead of the roof. Try removing the vent from the dryer and placing the vent pipe in a bucket and see if you get water especially if it is raining. If you can look up the pipe and see if you can see daylight, if it is a big open circle (assuming round duct) the vent trap door is missing or stuck open.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.