Dryer Vent Safety - Cravens Home Inspection Tulsa

Dryer Vent Safety - Cravens Home Inspection Tulsa
Dryer Vent Safety
The #4 leading cause of house fires is blocked dryer vents; which results in over 12,000 dryer vent fires
each year. Reduced air flow caused by restricted dryer vents resulting in high temperatures in the
dryer creates a huge fire risk.
When homeowners fail to perform regular maintenance on their dryer vents, they can become clogged. If a
spark from the dryer reaches this clog, the trapped dust and lint can ignite.
Clothes dryers evaporate the water from wet clothing by blowing hot air past them while they tumble inside
a spinning drum. Heat is provided by an electrical heating element or gas burner. Some heavy garment loads
can contain more than a gallon of water, which during the drying process will become airborne water vapor
and leave the dryer and home through an exhaust duct (more commonly known as a dryer vent).
A vent that exhausts moist air to the home exterior has a number of requirements:
It should be connected. The connection is usually behind the dryer but may be beneath it. Look
carefully to make sure it’s actually connected!
It should not be restricted. Dryer vents are often made from flexible plastic or metal duct, which may
be easily kinked or crushed where they exit the dryer and enter the wall or floor. This is often a
problem since dryers tend to be tucked away into small areas with little room to work. Vent hardware
is available which is designed to turn 90° in a limited space without restricting the flow of exhaust
air. Restrictions should be noted in the inspector’s report. Airflow restrictions are a potential fire
One of the reasons that restrictions are a potential fire hazard
is that along with water vapor evaporated out of wet clothes,
the exhaust stream carries lint – highly flammable particles
of clothing made of cotton and polyester. Lint can
accumulate in an exhaust duct, reducing the dryer’s ability to
expel heated water vapor, which then accumulates as heat
energy within the machine. As the dryer overheats,
mechanical failures can trigger sparks, which can cause lint
trapped in the dryer vent to burst into flames.
This condition can cause the whole house to burst into
flames! Fires generally originate within the dryer but spread
by escaping through the ventilation duct, incinerating trapped
lint and following its path into the building wall.
House fires caused by dryers are far more common than generally believed, a fact that can be appreciated
upon reviewing statistics from the National Fire Protection Agency. Fires caused by dryers in 2005 were
responsible for approximately 13,775 house fires, 418 injuries, 15 deaths, and $196 million in property
damage. Most of these incidents occur in residences and are the result of improper lint cleanup and
maintenance. Fortunately, these fires are very easy to prevent.
The recommendations outlined below reflect
International Residential Code (IRC)
EXHAUST guidelines:
M1502.5 Duct construction.
Exhaust ducts shall be constructed of
minimum 0.016-inch-thick (0.4 mm) rigid
metal ducts, having smooth interior surfaces
with joints running in the direction of air
flow. Exhaust ducts shall not be connected
with sheet-metal screws or fastening means
which extend into the duct.
This means that the flexible, ribbed vents
used in the past should no longer be used.
They should be noted as a potential fire
hazard if observed during an inspection.
M1502.6 Duct length.
The maximum length of a clothes dryer exhaust duct shall not exceed 25 feet (7620 mm) from the dryer
location to the wall or roof termination. The maximum length of the duct shall be reduced 2.5 feet (762 mm)
for each 45-degree (0.8 rad) bend and 5 feet (1524 mm) for each 90-degree (1.6 rad) bend. The maximum
length of the exhaust duct does not include the transition duct.
This means that vents should also be as straight as possible and cannot be longer than 25 feet. Any 90° turns
in the vent reduce this 25-foot number by 5 feet since these turns restrict airflow.
A couple of exceptions exist:
The IRC will defer to the manufacturer’s instruction, so if the manufacturer’s recommendation
permits a longer exhaust vent, that’s acceptable. An inspector probably won’t have the
manufacturer’s recommendations, and even if they do, confirming compliance with them exceeds the
scope of a General Home Inspection.
The IRC will allow large radius bends to be installed to reduce restrictions at turns, but confirming
compliance requires performing engineering calculation in accordance with the ASHRAE
Fundamentals Handbook, which definitely lies beyond the scope of a General Home Inspection!
M1502.2 Duct termination.
Exhaust ducts shall terminate on the outside of the building or shall be in accordance with the dryer
manufacturer’s installation instructions. Exhaust ducts shall terminate not less than 3 feet (914 mm) in any
direction from openings into buildings. Exhaust duct terminations shall be equipped with a backdraft
damper. Screens shall not be installed at the duct termination.
Inspectors will see many dryer vents terminate in crawlspaces or attics where they deposit moisture, which
can encourage the growth of mold, wood decay, or other material problems. Sometimes they will terminate
just beneath attic ventilators. This is a defective installation. They must terminate at the exterior and away
from a door or window! Also, screens may be present at the duct termination and can accumulate lint and
should be noted as improper.
M1502.3 Duct size.
The diameter of the exhaust duct shall be as required by the clothes dryer’s listing and the manufacturer’s
installation instructions.
Look for the exhaust duct size on the data plate.
M1502.4 Transition ducts.
Transition ducts shall not be concealed within construction. Flexible transition ducts used to connect the
dryer to the exhaust duct system shall be limited to single lengths, not to exceed 8 feet (2438 mm) and shall
be listed and labeled in accordance with UL 2158A.
In general, a home inspector will not know specific manufacturer’s recommendations or local applicable
codes and will no be able to confirm the dryer vent’s compliance to them, but will be able to point out issues
that may need to be corrected
Annual dryer vent cleaning is a safe and affordable way to reduce your risk of a house fire. Not to mention,
it will reduce the amount of time it takes to dry a load of clothes. A dryer with a blocked vent can take 3 to 4
times as long to dry a load, therefore increasing the amount of energy and money.
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