How do you know that the duct you fabricate and install will hold up under normal use? Could superimposed loads, structural stress or even normal pressurization cause the ducts to leak or collapse?

A standard that includes laboratory test procedures for the evaluation of hvac air ducts has been lacking. But a new standard has arrived, ANSI/ASHRAE/SMACNA Standard 126-2000 that may solve some of these shortcomings.

SMACNA director of technical services John Stratton said this work was a long time coming, and will prove useful to the industry. He says having ANSI status means the resulting document will be seen as "very credible."

The foreword to this document states: "A standardized set of comprehensive tests can be used to make sure products meet minimum structural requirements, as well as to allow products to be compared to each other. SMACNA's "Hvac Duct Construction Standards - Metal and Flexible," has a chapter on testing but it is not as extensive as the new standard. Stratton predicts, although it is ultimately up to the committee, that the next edition of the SMACNA document will incorporate this information.

The standards project committee SPC126 was formed to develop standardized methods of testing to determine the strength and durability characteristics of hvac ducts under various loading and environmental conditions. To the committee's knowledge, no other publication covers all of the structural and durability tests as comprehensively as this standard, although individual tests are covered under other standards. The intent of this standard is to cover any duct shape and material.

According to the standard, "Structural testing determines the strength of a duct assembly under internal and external loading. Leakage tests are conducted to evaluate containment of flow and to determine the effect of individual tests or a series of tests. Deflection under pressure simulates the internal pressure loading on an installed hvac system. Deflection under superimposed loads determines the resistance of a duct assembly to deflect due to insulation, a snow load, and other types of superimposed loads."

The cost of Standard 126-200 is $32. It may be purchased through ASHRAE at 404-636-8400 or online at www.ashrae.org.

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