(as) hot as blazes
Extremely and uncomfortably hot. On summer days in Texas, when it's hot as blazes 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 blazes in the costumes they make us wear.
hot as blazes
Also, hot as hell. Extremely warm, as in It was hot as blazes in that room, or I'm hot as hell and would love a cold shower. The first of these hyperbolic similes dates from the mid-1800s, the second from the early 1900s.