California Institute for Energy and Environment (CIEE)

Duct leakage is a major source of energy loss in residential buildings. Most duct leakage occurs at the connections to registers, plenums, or branches in the duct system. At each of these connections, a method of sealing the duct system is required. Typical sealing methods include tapes or mastics applied around the joints in the system. Field examinations of duct systems have shown that taped seals tend to fail over extended periods of time. The Lawrence Berkeley National Laboratory (LBNL) has been testing sealant durability for several years using accelerated test methods and found that typical duct tape (i.e., cloth-backed tapes with natural rubber adhesives) fails more rapidly than other duct sealants. The test results for collar-toplenum connections showed that the current UL testing and certification program is not sufficient for indicating durability and many tapes showed significant failure when testing using UL 181B procedures. The current study focused on evaluating UL181B-FX duct sealants on round flex duct to sheet metal collar connections that placed less stress on the joint to be sealed. After two years of testing, the flex-to-collar connections showed little change in air leakage, but substantial visual degradation from some products. A surprising result from the testing was that most of the clamps used to mechanically fasten the connections failed during the testing. This indicates that the durability of clamps also need to be evaluated to ensure longevity of the duct connection. Testing also included advanced tape products being developed by major manufacturers on a collar-to-plenum connection as used in previous studies. The advanced tape performed better than previously tested cloth backed tapes and failed after about 60 days of testing. During this study we completed an ASTM standard (E2342-03) for evaluating the durability of duct sealants using the collar-to-plenum connection.