Is your air conditioner or heating unit blowing into the attic ?

Many homes have developed leaks in the ductwork, causing your heated or cooled air to blow into the attic. Duct leakage can be as high as 25 percent, without any obvious signs. Ducts either come loose and separate at connection points, or they can develop holes and leaks in the seam areas. 

Despite the name, however, don't use duct tape. Duct tape gets very dry in hot attic conditions and tends to deteriorate. A better solution is either foil adhesive tape, or a substance called mastic that you apply with a paintbrush.

The foil adhesive tape is pretty much what it sounds like...a roll of aluminum foil with a very strong adhesive backing on it.  A picture of several rolls is shown to the right.

Also pictured are containers of mastic, as well as a section of duct that has been repaired with the mastic paste.  The mastic is available in a caulk-style tube, or in bulk quantities in a bucket.