I don't know how F is implemented but in a lot of stack languages printing to the terminal isn't really a side effect. Every function takes the state of the entire world as it's one and only parameter and returns a new world.
Also heats up the room.
Exactly. If the program won't read it (the printout) back, or unless it is designed specifically to sense the heat, then, strictly speaking, it's not a side effect (in the particular sense in which a side effect may reflect on the program execution).
Yet it prints stuff to the terminal.