This Third Edition of the SMACNA commercial metal and flexible duct construction standards is another in a long
line dating from the 1950s. A quick overview of the changes is provided in the front of this manual.
SMACNA expresses appreciation to the many who have offered suggestions for constructive improvement in the fabrication and installation of duct systems. Suggestions for future improvement are welcome. Special thanks is given
to those who volunteered their time, gave special knowledge and struggled with development of a consensus that
would reflect the needs for a diversified industry. Although standardization intrinsically involves selection, no intention of discrimination against the use of any product or method that would serve a designer’s need equally or better
exists.
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