Clothes Dryer Vent Leaks in Ceiling

DEAR TIM: I live in a condo on the ground floor. My dryer is located in a closet in my bedroom. My dryer duct is routed from the back of my bedroom out into my living room ceiling where it connects to the dryer vent. Lately I have noticed a leak in my living room ceiling. The plumber found the dryer vent to be leaking at the elbow. What could be causing this? Please help, I'm living with a large hole in my ceiling and am unsure what to do. Alexandra N., Bedminster, NJ

DEAR ALEXANDRA: The leak is being caused by condensation that is forming either inside or outside of the actual clothes dryer vent pipe. That part of the pipe is getting cold and the very moist hot air from the clothes dryer is turning into liquid water as it gets closer to the exterior of the condominium's exterior wall. To stop the leak, you must keep the entire length of dryer vent pipe nice and warm.

To do this job correctly, you may have to enlarge the hole in the living room ceiling to expose the entire length of the dryer vent pipe. This may seem radical, but the drywall repair person can fix a larger hole in just about the same time as it takes to fix the small one created by the plumber who discovered the source of the problem.

I have found that it is often best to vent fans and dryers through the roof. I urge you to watch this video of mine to see how easy it is to install the correct vent-cap flashing on a roof. Have no fear - if done right you will have no leaks.

First, you need to caulk around the hole in the exterior wall where the dryer vent pipe exits your condominium. I'm willing to wager that cold air is leaking in this location and it allows the exhaust pipe to get cold. But only perform the caulking if the correct exhaust pipe is installed.

Clothes dryer vent pipes should be made from smooth, rigid metal dryer duct of at least 4 inches and no longer than 25 feet. Be sure that you have a minimum amount of 90 degree bends in the pipe. Each 90 degree bend produces the same amount of resistance to air flow as ten linear feet of straight pipe. Most clothes dryers limit the total length of vent pipe run, so you must pay attention to this installation requirement. You can find this information in the clothes dryer instruction manual.

If you use either of the metal pipes, tape all seams with real heating and cooling duct tape. This tape is meant to be used on steel or aluminum ducts. Do not confuse it with the common gray duct tape sold in all hardware stores and home centers. Heating and cooling duct tape has special adhesives and often a very shiny outer surface.

The final step it to completely insulate the outside of the clothes dryer vent pipe as it travels across the entire living room ceiling to where it exits your condominium. The insulation must be expertly installed and no part of the metal vent pipe must be exposed. You can use regular fiberglass insulation for this task. If you simply want to fill the entire joist space cavity with insulation, that will work. If you want to just wrap the pipe with thinner insulation, be sure you use the special duct tape to keep the insulation tight around the dryer vent pipe.

Once you have performed all of this work, it is time to repair your ceiling. Be sure there is plenty of insulation in the ceiling joist cavity near the outside wall. If you decide to just insulate the pipe, then be sure to completely fill the cavity with fiberglass insulation extending back four feet from the exterior wall towards the center of the room. This will block the cold from entering the ceiling cavity where the clothes dryer vent pipe is located.

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