I am working in my unfinished basement to seal our duct work to prevent the leakage of air from the gaps. There are a few larger gaps and many smaller. In talking to one local HVAC company, they use mastic. Another uses more tape than mastic. Code locally seems to use either foil tape OR mastic.
I have tried searching multiple places and cannot find a solid reason to use one over another. I am leaning towards foil tape since I have more experience with it. Does anyone have any advice on this?