What about for indoor temperature?

Question

If "Il fait chaud" is only for outside, how would you say, "It is hot" when indoors, meaning the temperature of the room you are in?

Answer

Bonjour Melisa,
«Il fait chaud» is French for it is hot, whether indoors or outdoors. Here is a link written by Laura:
https://www.lawlessfrench.com/vocabulary/weather/
and of course by Aurélie that is noted with your question above.
My French teacher uses the same expressions whether we are in the classroom or outdoors to express the observation about the weather, le temps or the weather forecast, la météo.
To the best of my knowledge, there is NOT a separate vocabulary for discussing the temperature inside a building; however, there may be some expressions that are unique to being inside since the wind isn't blowing indoors, il ne fait pas du vent à l'intérieur.
J'espère que ma réponse vous aiderait.
Bonne chance et bonne continuation dans vos études en français, la langue de Molière et qui a été utilisé par le monde français depuis l’époque d’Hugues Capet