Gaps in heating and air-conditioning ducts can be sealed with almost any kind of tape, with only one surprising exception--duct tape, according to researchers at the Lawrence Berkeley Laboratory. Max Herman and Iain Walker tested a variety of sealing materials, including clear plastic tape, foil-backed tape, mastic, injected aerosol sealants and many different kinds of the ubiquitous duct tape under conditions that simulate the heat encountered in ducts, which are often in very hot attics.
"Of all the things we tested, only duct tape failed. It failed reliably and often quite catastrophically," said Sherman, whose results were reported in the July/August issue of Home Energy. They conclude that duct tape's glue is destroyed by heating. Full results are at http://homeenergy.org/898ductape.textd.html