The ductwork in our 30 year old house has started coming loose where it comes up through the floor. It's nailed to the subfloor, but in several places, the nails have come loose, leaving gaps of an inch or two between the duct and the subfloor. This lets bugs into the house and probably isn't too good for our heating and air efficiency.
What's the best way to re-hang the ductwork and remove these gaps? How much do I need to worry about breaking something while repositioning the 30 year old ducts?
The portion of the duct that goes to each supply vent is hung by one or two nails each on the left and right sides. The nails have either come loose from or gradually tore through the plywood subfloor and fell out, or the nail gradually tore a hole through the duct (so it's still in the subfloor and the duct is hanging beneath it).
I hope that I'm using these terms correctly. Here are some photos.
Note the nail hanging on the left after it came out of the subfloor. There's another nail on the left (not visible) that's still in the subfloor, but the weight of the duct pulling on the nail apparently caused a vertical tear through the duct, letting it fall. There's a 3/4" vertical gap on the left between the duct and the subfloor and a smaller gap (but still enough to let in a draft) at the top where the duct no longer fits properly because it's hanging off the left.
Another supply vent. The nails have fallen on both sides, so this duct is apparently supported by nothing in particular, leaving about 2-3" vertical gap all around. The subfloor looks pretty worn, so I'm not sure that nailing it on each side as was done before would work very well.