ASHRAE Journal - May 2014 - 98

Column Hvac applications
Dan Int-Hout

The Deal About Duct Lining
By Dan Int-Hout, Fellow aSHRae

The ASHRAE MTG-EAS (Energy Efficient Air Distribution Systems Committee) in their
circulated draft (see my March column, "High Performance Air Distribution Systems"
March 2014) questioned the inclusion of lined duct sound attenuation in room noise
calculations. Presently, room sound levels in manufacturer's catalog typically include
5 ft (1.5 m) of lined duct, which could lead to overestimated sound levels.
All VAV terminal unit manufacturers rate performance
of their products with exposed fiberglass insulation;
some may rate them with other types of linings, such as
foil-faced, polymer, perforated wall, or solid wall liners.
While the units may not be rated by every supplier, the
acoustical adjustments for the different linings are available within most manufacturers' selection software. In
fact, AHRI will likely make these acoustical adjustment
values "publicly available" in the near future.
Except in a few locations in the U.S. or where prohibited, such as hospitals, using duct lining is common
practice. Some individuals (well-intentioned, of course)
have banned exposed fiberglass, citing it as a health concern. Making a reasonable deduction, one would assume
that if lining is prohibited in the ductwork that it would
be prohibited in the VAV terminal units as well. This is
not always the case.
For those occasions where liners are prohibited, acoustical calculations for the space need to include proper sound
data for VAV terminal units. Only a few manufacturers
provide values in printed catalogs for unlined duct and
unlined (or non-exposed) VAV terminal units. Their selection programs, however, can facilitate this determination.
So what is the big deal about duct lining?

Facts about Fiberglass Insulation
While there are some widely known facts about fiberglass liner and its applications, you may be surprised
to learn just how much misinformation there is in the
market today. Here, we break down the facts.
n
While fiberglass insulation on the skin does tend to
itch, by itself, it is actually not a health hazard. The fibers
are in fact too large to be ingested into the alveoli of
the lungs and do not have the jagged edges of asbestos,
which causes mesothelioma.
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Duct insulation is required to pass rigid duct erosion

test standards. ASHRAE Standard 62.1-2013 states:
5.4 Airstream Surfaces. All airstream surfaces in equipment and ducts in the heating, ventilating, and air-conditioning
system shall be designed and constructed in accordance with the
requirements of the following subsections.
5.4.1 Resistance to Mold Growth. Material surfaces shall
be determined to be resistant to mold growth in accordance with a
standardized test method, such as the "Mold Growth and Humidity
Test" in UL 1813, ASTM C 1338 4, or comparable test methods.
Exception: Sheet metal surfaces and metal fasteners.
Note: Even with this resistance, any airstream surface that is
continuously wetted is still subject to microbial growth.
5.4.2 Resistance to Erosion. Airstream surface materials
shall be evaluated in accordance with the "Erosion Test" in UL
1813 and shall not break away, crack, peel, flake off, or show evidence of delamination or continued erosion under test conditions.
Exception: Sheet metal surfaces and metal fasteners.
n
Take note of the listed exceptions in the above excerpt:
"Sheet metal surfaces and metal fasteners." These exceptions are listed because the oils left on sheet metal duct
during fabrication have been shown to support mold growth.
That's right, bare sheet metal can support mold growth;
fiberglass insulation on its own, however, cannot.
n
Extensive studies by insulation manufacturers and
the Thermal Insulation Manufacturer's Association
(TIMA) show that when glass fibers become detached,
they do so almost immediately (at initial system startup)
and pose no risk of detachment over time.

Mold Growth and Fiberglass
n
Fiberglass has the ability to trap dirt, which left at the
right conditions, may support mold growth. Sheet metal

Dan Int-Hout is a chief engineer at Krueger in Richardson, texas. He is a member of
SSPC 55, SPC 129 and consultant to SSPC 62.1.

ASHRAE Journal - May 2014

Table of Contents for the Digital Edition of ASHRAE Journal - May 2014