Nope not sex.. nor body heat.. but an action fire.. a burning bush.
Inferno, by Dante Alighieri
Obviously there’s some serious heat in this widely-read 14th century epic poem about hell. Wrongdoers are trapped in flamingtombs, plunged into rivers of boiling blood, immersed in individual flames, the soles of their feet burned. In the inner ring of the seventh circle, those violent against God or nature must lie on the burning sand while flames rain down upon them:
“Had there only been some shelter from the fire
I would gladly have cast myself down in their midst,
and I think my teacher would have indulged me.
As it was, since I would have been seared and baked,
fear overcame the good will that made me
hunger and thirst to embrace those men.” (Canto XVI)
The English Patient, by Michael Ondaatje
There may not actually be anything hotter than almost burning to death in the desert.
“I fell burning into the desert. They found my body and made me a boat of sticks and dragged me across the desert. We were in the Sand Sea, now and then crossing dry riverbeds. Nomads, you see. Bedouin. I flew down and the sand itself caught fire. They saw me stand up naked out of it. The leather helmet on my head in flames. They strapped me onto a cradle, a carcass boat, and feet thudded along as they ran with me. I had broken the spareness of the desert.”
The Great Gatsby, by F. Scott Fitzgerald
It is in the unbearable heat of the hottest day of summer that Daisy invites Gatsby, Nick and Jordan to lunch, and Tom realizes that his wife is in love with someone else, leading to his explosive confrontation with Gatsby.
“The next day was broiling, almost the last, certainly the warmest, of the summer. As my train emerged from the tunnel into sunlight, only the hot whistles of the National Biscuit Company broke the simmering hush at noon. The straw seats of the car hovered on the edge of combustion; the woman next to me perspired delicately for a while into her white shirtwaist, and then, as her newspaper dampened under her fingers, lapsed despairingly into deep heat with a desolate cry.”
You can read the rest of the selections here Burning Books: The Hottest Scenes in Literature