The efficiency of air distribution systems has been found to be 60-75% or less in many houses because of insufficient and/or poorly installed duct insulation and leaks in duct systems. Properly designed and installed duct systems can have efficiencies of 80% or more for little or no additional cost, potentially saving a homeowner $50-200 or more per year in heating and cooling costs.

“Is it OK to use duct tape?” The answer is simple: “A duct repair should last as long as the ducts themselves.” Consequently, that rules out most types of duct tape that one can normally purchase for duct sealing. The fabric-backed, rubber-based adhesive duct tape that can be bought at the neighborhood hardware store will fail rapidly when subjected to the conditions of temperature, humidity, and pressure normally encountered in ducts. Only UL approved tapes (marked clearly on tape) are approved but they MUST be applied to clean, dry surfaces or they could fail.

The best general answer for sealing is a special UL Listed (not just UL Classified) adhesive paste called mastic (preferably one that is specially formulated for duct repair). UL Classified mastic tests mainly for problems relating to fire, whereas UL Listed mastic tests for many things, of which the most important for our purposes is co-adhesion (holding ability and elasticity).