I don't technically have in-floor heating. But between my squirrel infestation last year and whatever chewed the hole into the corner of my bedroom floor, I doubt the 50-year-old ducts are in great shape. So all of the heat that leaks out of them essentially creates - radiant flooring! Ta-DA! (Kind of nice, since there is only one heat vent upstairs anyway)

(Ducts are b/t first and second floors - I don't have a/c, so I can't figure out why they did that. The first floor is never going to be warm.)