Air leakage in ducts has been identified as a major source of energy loss in residential buildings. Thirty to forty percent of airflow leaks in and out of ducting systems in residential buildings, and most of the duct leakage occurs at the connections to registers, plenums or branches in the air distribution system. The seminar reports on a recent study, which is a continuation of previous studies conducted by the Energy Performance of Buildings group, whose objectives are to develop new test methods for duct sealant longevity, evaluate different sealant types (e.g., tape, mastic, aerosol), facilitate the development of consensus standards (e.g., ASTM), and technology transfer. Two high temperature longevity tests were conducted. The first test involved the aging of common ”core-to-collar joints” of flexible duct to sheet metal collars, and sheet metal ”collar-to-plenum joints” exposed to continuous 200 Deg. F (93 Deg.C), 90 Pa circulating air. The second test consists of baking duct tape samples in a constant 212 Deg.F (100 Deg.C) oven following the UL 181B ”Temperature Test” requirements. These tests showed that the duct tape performance in sealing joints depends on the joint's geometrical dimensions; it gets worse as the number of dimensions required to describe the joint increases (1-D to 3-D). 1-D joints are the easiest to seal with duct tape, and thus the least to experience failure. However, these type of joints are rarely seen in installations. 2-D joints, such as the flexible duct core-to-plenum joints tested in this study, are less likely to fail than 3-D joints, as the shrinkage could have a positive effect in tightening the joint. 3-D joints, such as the common collar-to-plenum tested in earlier studies and this study as well, are the toughest to seal, and therefore the most to experience failure. This is essentially caused by the shrinkage of the duct tape backing that results in the peeling of its rubber-based adhesive off the sheet metal. The UL 181B baking test results showed that the failure in the duct tape joints can be attributed to the type of combination of the duct tape and the material it is applied to, as the duct tape behaves differently with different substrates.