The most common place for duct leaks to occur is where the duct penetrates the sheet rock at the ceiling. The top photo is of one that is unsealed. I see ducts like this that have been sealed in other places including those subsidized by power company sealing programs.
Many people seal the least leaky areas and are therefore mostly just reinforcing the duct. If the average size of these leaks at the ceiling is 1/8 inch times the perimeter of the duct box and the average or small house has 8 ducts... This adds up to about 36 square inches. Imagine how much energy is wasted by a 6" by 6" hole in your A/C duct !
Many people seal the least leaky areas and are therefore mostly just reinforcing the duct. If the average size of these leaks at the ceiling is 1/8 inch times the perimeter of the duct box and the average or small house has 8 ducts... This adds up to about 36 square inches. Imagine how much energy is wasted by a 6" by 6" hole in your A/C duct !
The right way to do it is to dig in the insulation and expose the leak first. Then seal with a latex based sealant that has fiber in it. as shown in the second photo.
