Gaps in joints and at connections in your ductwork can cause your heating and cooling bills to increase by as much as 20%*. They can also allow air contaminants to enter the home. Sealing your ducts is the best way to fix the problem permanently.
When sealing your ducts, the recommended materials include duct sealing mastic, UL-181 aluminum tape, and high quality caulking or foam sealant. Mastic is the most effective material to seal all types of ductwork and can be purchased in tubs or caulk tubes. Mastic looks like drywall joint compound and dries in hours. It sticks well to most surfaces and requires little preparation.
For larger gaps, a fiberglass mesh tape serves as a backing, and is then covered with mastic. Mastic and better grades of duct tape can be purchased from heating and air conditioning supply houses which cater to commercial contractors. These better-grade tapes cost more than standard products. However, cheap tape is no bargain as it can lose its seal within months.
* Source: ENERGY STAR® -www.energystar.gov