On Mon, 18 Jun 2007 07:35:09 -0700, DerbyDad03
wrote:

When the AC is being used, my basement tends to get about 5 degrees
cooler than the first floor. The basement is used for laundry, storage
and my workshop, so it doesn't need to be that cold.

Here's my idea: Cut a hole in my return trunk, near the floor, to
recapture the cooler air and send it back upstairs. I'd install a
filter and design it so it could be easily sealed up in the winter.

So, if this isn't a ridiculously bad idea, how would I go about
determining the correct size for the opening?

I like the idea.

Just provide both a supply and return to the basement and your other
rooms should be cooler. By supply, I mean to allow the supply to the
nearest room to enter the basement before being sucked back to the
evaporator.