Seal ducts and close basement doors.

Many homes with central heating have ducts which run through the attic and crawl space. If the seams in these ducts are leaky, especially in the attic, they can draw in hot summer air which flows into the house, creating more of a load for air conditioners. Minor duct repairs are easy to accomplish, and usually involve folding or crimping the tin edges with a pliers. Ducts in unconditioned spaces, however, should be sealed and insulated by qualified professionals using the appropriate sealing materials.

Air ducts which lead to your basement should also be shut off, as this part of your house usually cools itself naturally. Keep the door to the basement closed, as cool air will settle down to the basement where it isn't needed.