From Longman Dictionary of Contemporary Englishhot airˌhot ˈair noun [uncountable] things that someone says that are intended to sound impressive but do not really mean anything or are not true The theory was dismissed as a lot of hot air.
Examples from the Corpus
hot air• Today, however, most recommendations are known to be hot air and tail-covering platitudes.• Too much hot air and not enough plan.• You think this stuff about flying is a lot of hot air. 