Dryer Booster Fans White Paper

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A new name for Dryer Booster Fans
uch preferences often result in longer duct runs with multiple bends
and turns that impair dryer efficiency and interfere with a builder’s ability to
meet building code. A properly applied dryer booster fan, preferably one that
meets the latest UL Standard, may be the only solution that makes everyone
happy – including the home inspector and the local fire chief.
The 2012 International Residential Code (IRC) is pretty specific when it
comes to dryer exhaust venting. The maximum length for dryer exhaust duct
cannot exceed 35 feet from the dryer location to the wall or roof termination.
Each elbow reduces this maximum allowable length by 5 feet since the
restricted airflow that these fittings create is more than the same length
of linear duct. Manufacturers also have their own specifications for duct
length, so contractors should refer to the manufacturer’s instructions, as
well, to make sure the dryer duct length does not exceed a particular model’s
capability. Given these restrictions, it is highly likely that dryers located in
interior spaces will exceed either the IRC or the manufacturer’s limits on
duct length.
No builder wants tell a homeowner he or she can’t have the laundry room
located where they want. Rather than disappointing the client or simply
keeping his fingers crossed that the building inspector won’t notice the extra
long exhaust duct, a builder may decide to install a device that compensates
for the added restriction in an overly long duct in order to maintain airflow,
thus assuring that hot, moist, and lint-laden air is safely exhausted to the
outside. These devices, commonly known as “booster fans”, incorporate a
pressure-sensing switch that automatically turns the fan on when the dryer
is energized and helps overcome the resistance created by the additional
duct.
For years, these fans have been applied with great success in homes with
excessively long dryer exhaust duct runs. And many homeowners, once
burdened with long dryer cycles and perpetually damp clothes, have been
delighted with the results.
“Driers, Fires and Codes, Oh My…!”
As common as the need is for this type of device, and as frequently as
“dryer booster fans” are applied in the field, a lot of misunderstanding exists
regarding whether or not they are allowed per common building codes.
The short answer is, yes they are, except in rare cases where local
jurisdictions have specifically amended their own code to exclude them. The
IRC has never prohibited the use of auxiliary fans to facilitate dryer exhaust,
so why is there so much confusion over the application of a product that
solves such a common problem? The answer involves a complex chain of
events that begins with the fact that clothes dryers are a leading cause of
home fires.
It is virtually undisputed that the primary cause of dryer fires is lint build-up
in the dryer cabinet—mostly due to homeowners’ failure to routinely clean
the lint trap. Nevertheless, safety concerns over the product erupted when
the Consumer Product Safety Commission (CPSC) launched an investigation
in 2005 into the fire safety of clothes dryers. Although dryer booster fans
have never been implicated as a precursor to clothes dryer fires, it was
discovered through the investigation that the Underwriters Laboratory (UL)
standard under which they were tested was inadequate. The test standard
(UL705) did not specifically explore the safety of such fans in a dryer booster
application. While UL set to work to implement more specific testing
procedures, the IRC temporarily dropped all reference to dryer booster fans
from the code—hence the industry confusion.
UL has since developed a supplement to UL705 that does specifically address
the safety of fans used to facilitate proper dryer exhaust and has given
the product a new name, Dryer Exhaust Duct Power Ventilator (DEDPV).
Consequently, when the IRC releases its 2015 building code, it will include
provisions for the specific use of DEDPVs.
In the meantime, dryer booster fans that have yet to achieve DEDPV
designation are still allowed in many if not most jurisdictions throughout the
United States by virtue of Section 104.11 of the IRC, which states:
"The provisions of this code are not intended to prevent the installation
of any material or to prohibit any design or method of construction not
specifically prescribed by this code, provided that any such alternative has
been approved. An alternative material, design or method of construction
shall be approved where the building official finds that the proposed design
is satisfactory and complies with the intent of the provisions of this code,
and that the material, method or work offered is for the purpose intended, at
least the equivalent of that prescribed in this code".
Distinguishing Features of DEDPVs
While fans of another name may be installed in dryer booster applications
(at least for now) UL has announced that all “DEDPV” products manufactured
after July 31, 2012 must comply with the new supplemented requirements of
UL705 for sale in the US market.
The new UL testing standards for DEDPV products are quite complex and
have been adjusted to pertain exclusively to the operation of ventilation fans
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