SMACNA 1143: First Edition; 7th Printing: January 2003

FOREWORD

SMACNA has published a procedure for leakage testing of so-calledmedium and high pressure ductwork since January 1965. It appeared in Chapter 10 of the high velocity (later high pressure) construction standards and in Chapter 8 of theBalancing andAdjustment ofAirDistribution Systems Manual of 1967 vintage. In the 1970's energy conservationmeasures led to a decline in the use of truly high pressure commercial HVAC systems. Now, greater concern with the amount of leakage in systems of less pressure has evolved.

New research in the leakage rates of sealed and unsealed ductwork has disclosed a need for a bettermethod of evaluating duct leakage. European countries introduced an evaluation approach using the surface area of the duct and the pressure in the duct as the basic parameters. SMACNA has concluded that this approach is far superior to the arbitrary assignment of a percentage of fan flow rate as a leakage criteria. The surface area basis highlights the effect of system size and is now the keynote of new SMACNA duct leakage classifications. It is expected that in the future industry will have correlated leakage classes with performance of particular sealant methods used on individual joint systems.

Leakage testing on job sites disrupts productivity, is costly and is generally not as beneficial as onemight expect.Relatedly, industry fails to recognize the extent that equipment that is inserted in-line in duct leaks. Few ratings for this are published. Designers must account for equipment leakage separately from duct leakage allowances as they evaluate system leakage. SMACNAencourages designers to specify equipment leakage control and to rely on prescriptive sealing of ductwork asmeasures thatwill normally lead to effective control of leakagewithout the need for extensive leakage testing.

Application of the information and guidance herein should facilitate design, improve system performance and reduce the difficulty of testing and balancing newly installed systems. SMACNAexpressed appreciation to all of thosewhose knowledge and effort led to the introduction of this new publication.