Mechanical
Benefits of Double-Wall, Insulated
Duct and Fittings
Damage
Protection
Our sheet metal outer shell protects the insulation from damage during
construction and maintenance. In outdoor applications, it protects the
insulation from damage caused by sun, wind, rain, snow, oxidation, and
other environmental factors.
Internal
Erosion Protection
High airflow velocities and turbulent air streams can erode internal insulation.
The sheet metal inner liner in our double-wall duct and fittings protects
the insulation. For applications where fiber erosion is of special concern,
we can supply ACOUSTI-LINE™ insulation with an erosion-resistant
acrylic coating. Our standard double-wall duct has been tested at an independent
laboratory according to UL-181 standard duct testing procedures for impact
and erosion resistance at an internal airflow velocity of 10,000 feet
per minute. These tests showed no evidence of insulation erosion and,
according to UL-181, our double-wall duct is rated for airflow velocities
up to 4,000 feet per minute.
Antimicrobial
Coatings
McGill AirFlow offers two types of antimicrobial protection with our double-wall
duct and fittings. ACOUSTI-LINE insulation is available with an acrylic
coating formulated with an antimicrobial agent that is EPA registered.
The coating resists the growth of fungus and bacteria, as determined by
tests in accordance with ASTM C 1071 and ASTM G21 and G22. For added protection
against microbial growth, the coated surface can be cleaned according
to the procedures detailed in the North American Insulation Manufacturers
Association (NAIMA) Duct Cleaning Guide. Our double-wall product line
is also available as SilverGuard™ duct and fittings. SilverGuard™
ductwork is pre-coated with an antimicrobial compound. It is a second
line of defense in the control of bacteria, molds, mildew and other fungi
found in HVAC duct systems. The inner wall of the outer shell and both
walls of the inner shell can be coated.
Low
Friction and Dynamic Pressure Loss
The inner liner in a double-wall system presents a uniform cross section
for airflow, resulting in nominal pressure losses essentially equal to
those of single-wall duct and fittings. Since sheet metal screws used
in the assembly of double-wall duct are hidden in the insulation, they
do not project into the airstream where they can increase pressure loss.
We install insulation in our double-wall duct and fittings at the factory,
reducing your field-installation time by eliminating the job of applying
external insulation. The components of a double-wall duct system are joined
by specially designed double-wall slip couplings and fitting collars.
These have an extended inner collar so that the inner liners can be mated
before the outer shells are mated. This two-step assembly procedure eliminates
alignment problems during installation. For more detailed information
about installation, refer to our Installation of Double-Wall Duct and
Fittings brochure.
Fire
Safety
The sheet metal walls of our double-wall duct and fittings are noncombustible
and not prone to penetration by fire. The surface burning characteristics
of the insulation are equal to or lower than the acceptable maximum values
given in the National Fire Protection Association (NFPA) standard 90A.
Automatic
Expansion Joint
The inner liners of our double-wall duct and fittings slip fit together
and do not need to be securely attached to each other. They are free to
expand and contract at the slip-fit joint, providing an automatic expansion
joint when there are temperature changes inside the duct system.
Appearance
Double-wall duct and fittings are ideal for use in architecturally exposed
applications. The sheet metal outer shell has a uniform, finished appearance,
and it can be painted to match or complement its surroundings. Externally
insulated duct systems have unattractive surfaces that are susceptible
to damage and difficult to paint.
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