If you’re planning to direct your dryer vent into a bucket of water next to the dryer, the IRC has one word for you: “Don’t.” You must terminate your dryer vent outside the building, according to section M1502 of the IRC. This also means that you can’t blow the dryer exhaust into the attic or the crawlspace. This regulation prevents lint from building up indoors and creating a fire hazard and warm, moist air from promoting rot and mold. The regulation prohibits screens at the outdoor vent termination — they collect lint which eventually blocks the vent.
Vent Material and Length
Running corrugated plastic ducts through the crawlspace may seem like a convenient venting solution, but it doesn’t comply with the code. Section M1502 requires that vents be constructed of smooth metal ducts fastened without screws that extend into the vent and collect lint. It is better to join the pipes with foil-backed duct tape. The vent should be as straight as possible, and the code sets a limit of 25 feet on its length. If you have to install bends, you should reduce this limit by 5 feet for every 90-degree bend and 2 1/2 feet for every 45-degree one.
According to the International Association of Certified Home Inspectors, the IRC defers to dryer manufacturers in specifying such details as the length of the vent and the number of bends it can contain. Some manufacturers design their machines to work with much longer vents. The IRC also leaves it up to the dryer manufacturer to specify the diameter of the vent hose to use. It allows homeowners to use one 8-foot length of flexible pipe to transition from the dryer to the exhaust pipe. This length of flexible pipe must remain visible and accessible so it can be removed and cleaned.