"Blowing hot air" is an idiomatic expression that means someone is saying something without meaning or simply lying. There are various other synonyms that can be used instead of this phrase. For instance, you might say that someone is "talking nonsense" or "spouting off." Alternatively, you could describe them as "spinning tall tales," "exaggerating," or "rambling." Another great synonym for blowing hot air is "empty rhetoric." This term emphasizes the lack of substance in what someone is saying. Using any of these phrases will help you sound more nuanced and precise when describing people who talk a lot without actually saying anything of value.