I've been sealing the ducts in our basement with mastic. I've done a decent job, but I'm trying to find every leak in the basement, where it's accessible.
For instance, I stand on the ladder in one area and I feel cold air with the a/c running. But, I can't figure out where it's coming from, and there are ducts on three sides of me, all within a foot of my head. If I hold up a 1 ply torn corner of a Klennex it flutters a bit but I can't determine which direction, let alone specifically where so I can throw a little more mastic there.
Everything I've read online is about testing leakage to get a number, etc. but I just want to know where exactly in the basement any leaks that are left are from.
I've thought about an incense stick, but am hoping for something with no chance of burning anything, something I can pick up and put down repeatedly with no worries.