- A typical 12-pound load of laundry weighs about 20 pounds when it emerges from the washer, meaning that a dryer has to dispose of about a gallon of water with every load. Because of the moisture, exhausting the dryer to the outside is recommended since indoor exhausting can cause mildew and other problems.
- There are several types of ducting materials available. They are listed below in order of preference:
- Rigid metal (aluminum or galvanized steel) - preferred
- Flexible metal (shown at right)- acceptable
- Flexible thin foil- unacceptable
- Flexible plastic - unacceptable
Facts To Consider
Underwriters Laboratories standards 560 and 2158 for clothes dryers require that all dryers listed must specify all metal dryer venting unless otherwise tested. A UL 181 label does not apply to dryer venting. Underwriters Laboratories Inc., an independent testing agency that helps set national safety standards, requires that dryer manufacturers
"include explicit instructions specifying that
only rigid or flexible metal duct should be used for exhausting, unless the appliance has been investigated for use with nonmetallic duct."
Maytag and other major dryer manufacturers recommend against the use of plastic flexible duct.
Although plastic flexible duct (cheap and easy to install) might seem like just the thing for exhausting a dryer, it isn't. This type of exhaust duct, which resembles a plastic-covered slinky toy, is not recommended for several reasons.
And as if that
weren't reason enough...
Safety Commission estimates there are over 15,000 clothes
dryer fires each year in the United States, amounting to
$96,000,000 in estimated property damage. Lack of
maintenance is the leading cause of dryer fires, and
LINT is the leading material to ignite. These fires
can be caused by failure of mechanical and/or electrical
parts within the dryer itself, improper materials being
put into the dryer, and insufficient airflow as a result
of improper installation.
- Read and follow the manufacturer's installation instructions.
- If at all possible, use 4-inch diameter rigid aluminum or rigid galvanized steel duct. Do not use smaller duct. If flexible metal duct must be used, use the type with a stiff sheet metal wall.
- Do not use flexible duct with a thin foil wall. Never use plastic flexible duct.
- Do not exhaust the dryer into any wall, ceiling, crawl space or a concealed space of a building, gas vent or any other common duct or chimney.
- Keep exhaust duct as straight and short as possible. Exhaust systems longer than the manufacturer's recommendations can extend drying times, affect appliance operation and may collect lint. These recommendations may vary somewhat for different brands and should be referenced when installing the dryer.
- The exhaust hood on the outside of the house should have a swing out damper to prevent backdrafts and entry of wildlife.
Never use an exhaust hood with a magnetic damper. The hood should have at least 12 inches of clearance between the bottom of the hood and the ground or other obstruction. The hood opening should point down.
- Never install a screen over the exhaust outlet
Builders & Contractors Note-
Do your clients a favor and do NOT install the laundry room in the
middle of a structure. This will require special venting considerations
for the dryer & usually results in poor dryer performance due to
vertical runs. Try and plan the laundry room to be on an exterior wall
if possible. New dryers will only carry the air & lint for about 18
feet, not including elbows and bends.
If your floor plan does not provide for external-wall venting, consider
installing an eave-vent system. A typical installation can be seen
remediate a roof-top vent run & cut several feet off of your exhaust run by
installing a simple Eave Vent for your dryer. It
won't have to run nearly as far, plus the exhausted lint will be directed
away from the house.
Just as a point of interest, a customer
sent the following:
As you suspected, clogged venting turned out to be the problem after all-- not in the 8 feet of aluminum exhaust piping from the dryer to the ceiling, nor at the elbow, nor in the first 5 feet of the conduit in the plenum that my shop vac hose could reach, but rather in the balance of the 28 feet total carry to the external wall vent.
The duct cleaning guys ran rotobrush brush agitator powered by en
electric drill as far as they could reach (23 feet). The drill rig clogged and shut down twice. Both times they retrieved the apparatus, they pulled out large 3-4 liter clumps of lint. Then, one of the men took the giant hose attached to their huge HEPA filtered collection device and pressed the end on the ceiling, surrounding the exposed portion of the elbow. After about 10 seconds of suction almost nothing appeared in the clear tube. The guy said, "I guess we got it all," when suddenly a series of really huge lint clumps -- equivalent in volume to about two sweatpant/sweat shirts sets, we found out later -- came whooshing down the pipe. Several of these large clumps were quite heavy from dampness.
The operator held the end of his flexible tubing flush to
the ceiling for about two more minutes, retrieving several more "minor" clumps of lint the size of two-liter soda bottles, before the suction ceased producing any more material.
Now the AutoDry sensor performs to spec, and a set of towels dries in 45 minutes, while normal laundry loads take considerably less time. I suppose we have also eliminated a potential fire hazard from our home.
I'll probably have the duct cleaning guys back in a few years, providing their apparatus extends the entire 28 feet. Some stuff may remain at the end where their rotobrush couldn't reach, although I now see steam pouring forth from the external wall vent when the dryer is in operation.
Without your advice, I doubt I would have concluded that the clog might be in the ceiling conduit, but thanks to you I had eliminated all other plausible avenues.
Thanks again and best regards",
How Dryer Vents Can
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