I have a 2 1/2 story house with only 1 return air duct. It is located at the end of the house, downstairs. With no place for the warm air to go, the upstairs stays 6-8 degrees hotter than downstairs. What can I do to get more uniform cool air distribution? Thanks

There is 2 approaches to this. You can try to fix it, or you can demand the previous owner fix it. I am sure the building codes demand adequate returns. How old is this house? This sounds like bad workmanship to me. If it is relatively new, talk to the builder. I don't think it is right to pay a fair price for an older house, and then force the seller to make it like new. On the other hand, there is a limit to non functional systems a buyer is stuck with. Talk to the previous owner/builder. If you don't like the answers, talk to the local building inspection/code enforcement officials. If you still aren't getting answers you like, then call a lawyer.

Installing returns is much easier before the house is drywalled. It is possible the returns are at least partly there, but somebody carelessly drywalled over them. If the original prints or drawing are available, it might be as simple as cutting some holes in the right places and installing grates. If the air return ducts are under the house, running ducts down from the second story will be tough. You can use an empty cavity in an interior first floor wall. Cut a hole into it from the top, and add a grate. Then cut a hole into it from the bottom, and duct it to the return air. If there is a second story wall where you want the duct, cut a hole in it at the bottom, and reach in and cut into the wall cavity, covering the hole in the wall with the grate. You may want to start with the easiest places first, and quit once the air circulated well enough. Good luck.

Thanks for the info. The house is 30+ years old