I'm seeing a crack in the corner of the ducts. Can I just tape it shut with boxing tape or is there a better way to do it?
Also, one register in an unfinished area is turned off but I can feel it leaking air. I looked inside and there's clearly a gap letting air past too. Can I also just cover the register in reflectix and tape that shut too or is there a better option? Thank you :)
I have to confirm that mastic plus aluminum tape is the way to go. The mastic will help fill the gap and protect the tape from drying out and peeling away. Be sure to clean it thoroughly so the tape will stick long term. Be generous with the tape as over time it may begin to fail. Mastic is doubly important if you have condensation issues. And if that is the case, or the duct work is in unconditioned space, you should consider insulating and covering the duct work.