Dryer Vents in Mobile and Manufactured Homes

The Federal Rule That Governs Manufactured Homes

A manufactured home is built to a federal standard written by HUD, and the dryer rule sits in 24 CFR 3280.708. Its first paragraph says every gas and electric clothes dryer is exhausted to the outside through a moisture and lint exhaust duct and a termination fitting. The next paragraphs add three limits that matter under a home: the duct is never connected to any other duct, vent or chimney; it shall not terminate beneath the manufactured home; and its joints are never made with sheet metal screws or other fasteners that reach into the duct.

The standard also covers homes that left the factory without a dryer. In that case the maker provides a roughed-in opening through the wall or floor with removable caps inside and out, designed to limit air leaks and keep out water and rodents, plus written instructions for completing the duct to the same rules. That capped hole is often the starting point when an owner adds a dryer later.

Why the Duct Has to Clear the Skirting

When a dryer exhausts down through the floor, the duct enters the crawl space between the floor and the ground, which the skirting closes in. A duct that simply stops in that space is terminating beneath the home, which the federal rule forbids. Warm, wet, lint-heavy air then fills an enclosed space under the floor, where it soaks insulation and the underside of the floor and leaves lint behind.

GE's installation instructions spell out the fix: if the dryer is exhausted through the floor, the exhaust must not terminate beneath the mobile home, and the termination must be securely fastened to the home's structure. Maytag says the vent is fastened to a noncombustible portion of the home and ends outside. In practice the duct runs under the floor to the skirting and passes through it to a hood with a damper on the outside face, or it exits through a side wall above the skirting instead.

• Floor exit: duct down through the floor, across under the home, out through the skirting to a fastened hood
• Wall exit: duct straight out through the side wall above the skirting line, often the shorter route
• Either way: 4 inch metal duct, no screws into the airstream, hood with a working flap

Air In, Not Just Air Out

A dryer has to draw in as much air as it pushes out, and a small laundry closet holds little air. GE's instructions call for an opening with at least 25 square inches of free area to bring outside air into the dryer room. Maytag asks for openings, such as a nearby window, at least twice as large as the dryer's exhaust opening. Without that, a dryer in a small laundry closet runs short of air, and drying slows. Maytag also requires a 4-wire power connection for an electric dryer in a mobile home, and GE asks that gas dryers be fastened to the floor with the maker's kit.

What to Look for Under the Home

The Consumer Product Safety Commission notes that plastic and foil duct traps lint more easily and is prone to kinks and crushing, which can greatly reduce airflow. Under a home, where nobody looks for years, a crushed hose is easy to miss. You can check the outside end safely from the yard while the dryer runs. Crawling under the home is a different job: tight spaces, insects, wiring and uneven ground make it a place to send a crew rather than go alone.

• A duct that ends in the crawl space, with a pile of lint on the ground below it
• A plastic or foil hose running under the floor in place of metal duct
• A section that has sagged, been crushed or pulled apart at a joint
• A hood on the skirting with its flap missing, stuck open or blocked by soil and plants
• Wet insulation or a musty smell near the laundry end of the home
• Signs of animals nesting in or around the duct

How a Failed Under-Home Duct Is Put Right

The repair usually starts by removing the old hose and any lint pile under the home. A new 4 inch metal duct is run from the floor collar, supported so it cannot sag, and joined with clamps rather than screws, which 3280.708 forbids inside the duct. It is carried out through the skirting, or rerouted through a side wall if that is shorter, to a hood fastened to the structure. Finally the makeup air opening for the laundry room is checked. That is the work our dryer vent repair visits cover.

The hose behind the dryer has its own limits, described in how long should a dryer vent hose be. A dryer in a garage or carport room follows the building code instead of the HUD standard; see how to vent a dryer in a garage.

Family-owned and local, we send an experienced crew that follows the duct from the dryer to the skirting before recommending anything. Proudly American, we start with a free inspection under and around the home and give you a written estimate before any work.