Duct tape may be a handy tool for a variety of tasks, but it's not the right choice for sealing ducts. Despite its name, general-purpose adhesive tape was not designed for use in HVAC ducts. If you try to use it, it won't work. It's not the right material for the job.
Adhesive tape is strong and can stick to even the toughest surfaces. But it doesn't hold up well to extreme changes in air duct temperature. Heating cycles can cause the adhesives on the adhesive tape to break down over time. The tape will weaken and eventually fall off.
Putty sealant and aluminum foil tape are better options for sealing air ducts. Don't be fooled by the name “duct tape” - it's not suitable for this purpose. Researchers have found that it allows too much air to escape or simply falls off after a few weeks or months. Rather than repeating this cycle, invest in a material manufactured for ducting or call an HVAC professional.
Hardcast recommends using Foil-Grip butyl tape with ducts, duct plates, or flexible galvanized steel ducts. If your indoor air is too dry, this could be a sign that there are a lot of leaks in your house and that hermetic sealing work is needed. Your technician will be able to seal all leaks in your duct system (even those in hard-to-reach sections). They'll also be able to clean and isolate them to increase efficiency and improve indoor air quality.
It's important to use the right product in the right place. After World War II, when the real estate market was booming, adhesive tape was made available to civilians and some manufacturers began selling it for connecting heating and air conditioning ducts. In 1998, researchers at Lawrence Berkeley National Laboratory (LBNL) conducted a three-month experiment to see if adhesive tape, along with 31 other sealants, could withstand typical air duct conditions. The results showed that it didn't work.
If your ducts are different from standard ones, you may need to replace the boots or seal the gaps with spray foam, putty, or canned adhesive tape. I used duct putty to seal the boots to the attic floors and then sealed the boots to the ceiling of my living room (before reattaching the grills). To match the ducts, the color of the tape was changed from an army green to a silver color. It works better on round ducts than on rectangular ones with sharp corners.
However, if your grill is sealed with adhesive tape and you need to replace it, you'll need to re-caulk it. If you're using putty to seal joints in fiberglass plate ducts, use fiberglass mesh tape for all joints. It's essential to use the right product for sealing ducts. Don't rely on adhesive tape - it won't hold up over time.
Invest in materials designed specifically for this purpose or call an HVAC professional for help.
