Years ago I worked in an office where the oversized computers we used to run EMS CAD software ran so hot that they provided enough heat to fill the room in the winter, making the office pleasantly toasty.
Another old device that generated plenty of excess heat was traffic lights with incandescent bulbs. But it turns out, as snowbound municipalities are just now discovering, that that excess heat was very useful for melting accumulated snow. Now that everyone's switched over to cooler-running LEDs, snow tends to pile up and obscure the lights, leading to a situation that's annoying at best and dangerous at worst.
For now, local governments are coping by sending crews out in snowstorms to clean the lights off with compressed air and brushes, as no one's yet stepped forth with a design-related fix.
And as the mercury continues to drop, I wish I had some of those old EMS boxes in my apartment right now--when it gets chilly in here I could run CAD, ask the machine to calculate a volume, then sit back and enjoy a blast of warm BTUs.