Duct tape may be a handy tool for fixing just about anything, but it's not the right choice for sealing ductwork. Despite its name, general-purpose adhesive tape was never intended for use in HVAC ducts. If you tried to use it, it would likely fail. Adhesive tape has many uses, but wart removal is one that comes to mind - not sealing air ducts! The tape can stick to even the toughest surfaces and withstand a lot, but it doesn't hold up well to extreme temperature changes in air ducts.
Over time, the adhesive weakens and eventually falls off. When it comes to sealing air ducts, putty sealant and aluminum foil tape are better options. In 1998, researchers at the Lawrence Berkeley National Laboratory (LBNL) conducted a 3-month experiment to see if adhesive tape, along with 31 other sealants, could withstand the typical conditions found in air ducts. The results showed that aluminum adhesive tape (also known as “roll adhesive tape”) is easier and less messy, but it tends to fail faster due to delamination and dirt and grease in the ducts.
If you're using putty to seal joints in fiberglass plate ducts, use fiberglass mesh tape for all joints. Adhesive tape works better on round ducts than on the sharp, uneven corners of rectangular ducts. You don't need an airtight seal between the grille and the cover if the cover is sealed to the plaster and the duct system is relatively airtight. Professional air conditioning tapes can stand up to the test of time, but they tend to be more expensive than putty sealants. To simulate typical conditions in air ducts, warm air (167 °F) and cold air (53.6 °F) were forced through several air ducts, each using a different type of sealant to keep the air inside.
The color of adhesive tape was changed from military green to silver so it would match the ducts. When sealing boots on attic floors with putty, use fiberglass mesh tape for all joints. And when sealing foam plate to a concrete stem wall, make sure you use a material made for ducts or call a professional HVAC technician. Investing in the right materials will save you from having to repeat this cycle.
