Common questions and answers about fiber glass insulation

- What factors should be evaluated before deciding to line or wrap air duct? If ductwork is located in a high traffic area where damage could occur easily, duct should be lined to protect the insulation.
By David Tomchak March 1, 2000

What factors should be evaluated before deciding to line or wrap air duct?

If ductwork is located in a high traffic area where damage could occur easily, duct should be lined to protect the insulation. Liner should also be used if acoustics, particularly concerns about cross talk from one office to another, are a problem. Depending on the density and thickness of the liner and length of the duct, ductwork with interior insulation can absorb anywhere from 50% to nearly 100% of the sound passing through it. In addition, it affords superior thermal control.

If thermal or condensation control is the concern, duct wrap is a better choice. Wrapped duct does not enhance sound attenuation, but does help deliver air at the desired temperature. In a heavy industrial setting in a cold climate, wrapping may be an option, although many plants use bare sheet metal for air handling because the industrial processes already generate heat into the workplace.

What are turning vanes in an HVAC duct system?

In an HVAC duct system, turning vanes assist the flow of air around 90-deg elbows to minimize pressure loss. Although many turning vanes are made of metal, molded acoustical fiber glass vanes are also available. They are manufactured with a specially treated exterior surface designed to eliminate the potential for fiber erosion and mold growth.

What is performance testing?

A performance test enables a technician to identify leaks and other performance problems. During the test, the duct system is pressurized while a calibrated fan simultaneously measures the flow of air through the fan and its effect on the pressure within the duct system. The tighter the duct system, the less air is needed from the fan to create a change in the duct system pressure. Testing procedures are available to measure leaks to the outside or total duct leakage.

Should sealants and encapsulants be used on HVAC duct systems?

Sealants and encapsulants that coat and seal duct surfaces are intended to prevent the release of dust and dirt particles into the airstream. However, little documentation exists on the effectiveness of these materials. Questions remain about whether the sealant materials deteriorate over time, whether or not they alter the surface burning characteristics or acoustic properties of the insulation, and about the potential toxicity of the products should they catch fire.

Can heating and cooling equipment be downsized with properly insulated ducts?

Plant engineers often oversize HVAC equipment just to be safe. However, in a retrofit, a properly insulated and maintained duct system may enable a plant engineer to reduce the size of the previously specified equipment.

What is the difference between rotary and textile fiber glass insulation?

The two most common processes used in manufacturing fiber glass insulation are rotary and textile. They show a nominal difference in performance properties on paper, but their installed performance characteristics are nearly equivalent. Textile fibers perform well in thermal and acoustical applications and provide a strong and durable insulation product. Rotary fibers provide incremental R-value (thermal resistance) and noise reduction coefficient (NRC)-value improvement over textile.