(as) hot as fire
Extremely and uncomfortably hot in temperature. On summer days in Texas, when it's hot as fire outside, there's nothing quite like a tall glass of sweet tea. I hate working in the theme park during the summer because it's as hot as fire in the costumes they make us wear.
*hot as fire
and *hot as hellvery hot; burning hot. (*Also: as ~. Use hell with caution.) I'm afraid Betsy has a high fever. Her forehead is hot as fire. It's as hot as hell outside. It must be near 100 degrees.