The hot air charm is an unnamed spell which fires off a jet of hot air from the end of the caster’s wand. Casting the spell involves a complicated wand motion (OP21).
“She pulled out her wand and gave it a complicated little wave so that hot air streamed out of the tip; she then pointed this at her robes, which began to steam as they dried out.”
References from the canon
- Newt Scamander - 1927 – used the charm to dry Jacob Kowalski’s “rain soaked clothes” with a blast of “warm magical air.” (CG).
- Hermione used this charm to melt snow and dry off her snow-covered robes (OP21).
- Dumbledore used something similar on Harry's wet robes, but the spell he cast instantaneously made the robes warm and dry and didn't involve any wasted wand motion (HBP26).