I recently had a conversation with my HVAC contractor. I asked him if there is a way to use the cool air in that pools in our basement. He told me that I could unscrew the cold air return vents and tape cardboard to the back of them. If I block all of the air returns, except those in the basement, the cool basement air will circulate to the upper floors. I'm anxious to try this trick next summer. It makes a lot of sense, but I'm surprised it isn't used more frequently. Hopefully it saves a lot of money.I’ll let you know.