When Pat went down into his crawl space to see if he could improve his duct sealing and reduce leakage, he found that the duct joints were sealed with duct tape that had long since become brittle and ineffective.
He also found the duct in the picture below -- a duct cap that had completely opened up due to a failure of the tape holding the cap in place. Amazing!
Check your ducts! and seal them properly -- there are two choices:
Duct Mastic is a thick paste like
material made for sealing HVAC ducts. It gives a high quality and long
lasting seal. This is
UL 181 approved duct tape. This is a tape made for sealing ducts, and will generally last much longer that ordinary duct/duck tape. However, this report indicates that even UL181 approved tapes may have a short life.
I would use the duct mastic -- its a bit messy, but not bad just applying it with your hand wearing a cloth glove. Don't rely on mastic or tape to keep ducts from separating, use screws to keep the ducts from separating, and mastic to seal.
This article from the Green Building Advisor site has a lot of in depth information and advice on sealing ducts....
Gary Mar 14, 2008