The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with hot air
Empty, exaggerated talk, as in That last speech of his was pure hot air. It is also put as
full of hot air, as in Pay no attention to Howard—he's full of hot air. This metaphoric term transfers heated air to vaporous talk.
[ Late 1800s