Sorting out the options in fiber glass duct insulation

Key concepts Fiber glass insulation is used in HVAC systems for temperature, noise, and condensation control, and energy conservation. Four primary types of products are duct liner, duct wrap, duct board, and flexible fiber glass ducts.


Key concepts

Fiber glass insulation is used in HVAC systems for temperature, noise, and condensation control, and energy conservation.

Four primary types of products are duct liner, duct wrap, duct board, and flexible fiber glass ducts.

Studies show fiber glass insulation does not contribute to microbial growth and has a positive impact on building IAQ.

For more than 40 yr, fiber glass insulation has been used as a component in air duct systems to maintain comfort and indoor environmental quality. HVAC fiber glass insulation is specified for four primary reasons:

- Temperature control -- Delivering heated or cooled air at a temperature level best suited to building needs

- Acoustical control -- Absorbing noise generated by air handling equipment and by air moving through ducts

- Condensation control -- Preventing condensation that could damage insulation and other HVAC system components

- Energy conservation -- Reducing HVAC system operating costs and energy use by lowering heat loss or gain through air duct walls.

More than 99% of all HVAC insulation products use fiber glass technology. The material remains an optimal choice in terms of safety, cost-effectiveness, and performance.

Types of insulation

There are four basic types of HVAC insulation products: duct liner, which is used in the interior of sheet metal ducts; duct wrap, which is used on the exterior of sheet metal ducts; fiber glass duct board, which is used to fabricate duct; and flexible fiber glass ducts.

1. Duct liner. Fiber glass duct liner products come as flexible blankets or rigid boards of fiber glass insulation. Either a coating or a fibrous mat may form the airstream surface. Liners are offered in a variety of thickness and density combinations from 1/2­2 in. Their tough airstream surface resists puncturing, tearing, and surface wear during fabrication, installation, operation, and cleaning.

Most duct liners contain an EPA-registered biocide to make them suitable for IAQ-sensitive jobs. Although most liner products are intended for application in square and rectangular ductwork, products specifically designed for round duct are available.

2. Duct wrap. Fiber glass duct wrap is applied to the outside of sheet metal duct. It is a blanket-type thermal insulation composed of glass fibers bonded together with a thermosetting resin. Duct wrap can be used for both round and rectangular duct. It normally has a vapor-retardant facing of foil scrim kraft (FSK) or vinyl. Unfaced duct wrap insulation is also available when vapor-retardant facing is not required. Rigid board insulation with reinforced FSK or all-service jacket facings (ASJ) are used as exterior insulation on large metal ductwork.

3. Duct wrap. Fiber glass ducts are fabricated from 1, 11/2, or 2-in. thick boards. The boards consist of insulation materials made from resin-bonded inorganic glass fibers. The outside surface of the board has a manufacturer-applied reinforced aluminum/FSK laminate facing that serves as an air barrier and water vapor retardant. Some products are available with mat-faced or coated airstream surfaces. Many contain a safe, effective EPA-registered biocide to protect against the growth of mold and mildew. Surfaces on these enhanced products can be easily cleaned using industry-approved methods.

4. Flexible fiber glass ducts . Flexible fiber glass insulated ducts consist of a spiral-wire-reinforced inner air core wrapped with fiber glass insulation and jacketed with a vapor-retardant reinforced foil or plastic film. These ducts provide an efficient, economical way to connect trunk ducts and room diffusers or registers. Flexible fiber glass ducts should be used in restricted lengths.

Effect of insulation on IAQ

A number of myths about the safety of fiber glass insulation have arisen over the years. Most question the impact of the material on a building's indoor air quality (IAQ) levels. It is unquestioned that the presence of water in HVAC systems is what contributes to mold growth. And mold is no more likely to grow on fiber glass than on any other surface in the duct system.

A study conducted by Duke University backs up this claim. Researchers examined the role of such environmental factors as temperature, humidity, airflow, operating hours, and presence of liquid in the enhancement of microbial growth in a ventilation system. They consistently found that microbial growth is greatest in wet zones, such as areas close to cooling coils, mixing boxes, and places where cold air mixes with hot, humid air and creates condensation.

Keeping the surface temperature above the dew point can greatly reduce the wet conditions that contribute to microbial growth. Fiber glass insulation can help control condensation, inhibit mold growth, and positively contribute to a building's IAQ.

Some specifiers have suggested that microbes use the binder and glass in duct liner as a food source and that microbial infestation can cause duct liner to degrade. A Harvard University School of Public Health study indicates this is not the case. The binders are not a nutrient for mold and do not amplify growth.

Others believe that glass fibers erode from the interior surface of fiber glass duct liner and board and become an irritant to workers. Study results from 25-yr ago are consistent with current research. The World Health Organization has declared that fibers do not have an adverse health effect on building occupants. The University of Nevada-Las Vegas also looked into the amount of exposure to occupants from manmade vitreous fibers when fiber glass insulation was used in air handling systems. That research confirmed that fiber erosion is not a significant issue.

Ensuring that an HVAC system continues to provide efficient, quiet air delivery, occupant comfort, and cost-effectiveness is best ensured with regular system maintenance. High-efficiency filtration is very important, as are regular inspections, adjustments, system balancing, and the draining of cooling coil trays.

-- Edited by Jeanine Katzel, Senior Editor, 630-320-7142,

The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
Pipe fabrication and IIoT; 2017 Product of the Year finalists
The future of electrical safety; Four keys to RPM success; Picking the right weld fume option
A new approach to the Skills Gap; Community colleges may hold the key for manufacturing; 2017 Engineering Leaders Under 40
Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
The cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Power system design for high-performance buildings; mitigating arc flash hazards
VFDs improving motion control applications; Powering automation and IIoT wirelessly; Connecting the dots
Natural gas engines; New applications for fuel cells; Large engines become more efficient; Extending boiler life

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
This digital report explains how plant engineers and subject matter experts (SME) need support for time series data and its many challenges.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me