Outlines UL 181A approved closure systems, recommended methods of reinforcement, support, and damage repair.

Includes a detailed job inspection checklist.

From the Preface
The North American Insulation Manufacturers Association (NAIMA) presents this Standard as a recommended method of fabricating and installing air transmission ducts in buildings using fibrous glass material as specified herein.

Rectangular ducts covered by this standard are designed to operate at 2" w.g. (500 Pa) static pressure or less and 2'400 feet per minute (12 m/sec) internal air velocity or less. Other duct configurations have been qualified for higher pressures and/or velocities.

Fibrous glass duct products are designed for use in comfort heating and cooling systems operating at internal air temperatures not less than 40 degrees (40 degrees C) and not greater than 250 degrees F (121 degrees C).

Underwriters Laboratories Inc. Standard for Closure Systems for Use with Rigid Air Ducts and Air Connectors UL 181A incorporates key provisions of the UL 181 Standard, as well as additional provisions developed by NAIMA and various closure material manufacturers. The resultant standard provides the means for assuring the contractor and building owner that the selected closure system will, when properly applied, perform within varied environmental conditions.

NAIMA acknowledges SMACNA's Fibrous Glass Duct Construction Standards, Fifth Edition, 1979, as a basis for the scope and content of the present document.

This standard was developed using reliable engineering principles and research, plus consultation with and information obtained form manufacturers, contractors, testing laboratories and others having specialized experience. They are subject to revision as further experience and investigation may show is necessary or desirable. Construction and products which comply with this standard will not necessarily be acceptable, if when examined and tested, they are found to have other features which impair the result contemplated by these requirements.

Dimensional data on 2" (51mm) thick fibrous glass duct board, with an R-value of 8.7 (RSI of 1.53), not having been widely used until recently, was not provided in previous editions of this standard, including the Fourth Edition (2001). This revised Fifth Edition includes thermal, acoustical, and dimensional data for 2" (51mm) duct board. For specific information relation to 2" (51mm) duct board only, refer to publication number AH-136.

The North American Insulation Manufacturers Association assumes no responsibility and accepts no liability for the application of the principles or techniques contained in this standard. In particular, NAIMA makes no warranty of any kind, express or implied, regarding merchantability or fitness for any particular purpose, in connection with the information supplied herein. Authorities considering adoption of this standard should review all federal, state, local and contractual regulations applicable to specific installations. This standard is not intended to preclude alternate methods and materials of fabrication, closure, reinforcement and support, when such methods and materials can be documented as providing equivalent performance.

A Note about the Use of Metric (SI) Units in this Standard
Two forms of conversion are used in this document:

• Critical fabrication dimensions, where accuracy is essential for correct fabrication, are converted from U.S. (IP) units (inches) to the nearest whole millimeter. Example: 2" = 102mm, 20" = 508mm.
• Where accuracy is not critical, or where dimensions are given as approximate, nominal or minimum/maximum, inches are rounded to the nearest 10mm SI value. Example: 2" = 100mm, 20" = 510mm.