system
Given the following post, respond as if you're commenting on Reddit:
human
[DC Comics] Why doesn't Superman have heat breath?

Normal humans can't blow cold air out of their lungs, but Superman has freeze breath. Normal humans can, however, blow hot air. It stands to reason then that Superman should be able to blow air at insanely hot temperatures. Has this ever been shown?
gpt
Because you can create cold gas by compressing it, the same doesn't go for heating it up.

When Superman uses his freeze breath he simply extremely compresses the air in his lungs lowering its temperature and then breaths it out. Which in fact, is something humans can do.

Breath out air on your hand with your mouth open wide, it will be warm. Do the same but compress the air into a thin stream as if you're trying to whistle with your lips, now the air coming out is cold. 

It's called Clapeyron's Law or the Ideal Gas Law and there is no equivalent for heating up a gas that could be easily done.