[cabmandone]

Today is the day we find out what the mystery stuff is! Wooo Hooo.

BTW Wayne, if ya get a chance post the A/C Model number and the High Fire rate for the furnace. I think I can put to rest a lot of assumptions by knowing these two things. I could tell you more if I knew the total number of supply registers and the corresponding duct size for each. If you're wondering where I'm going here, the rule of thumb is 6"=100cfm 7"=150cfm 8"=200cfm on the supply side. If add up the cfm for your supply, the return duct needs to be able to draw that much back. The big thing to know would be the exact size of that drop duct coming from the crawl space down into the bottom of the furnace and exact size of the flex duct. Again the variable being how kinked the duct is in the points you have pictured.