People often say heat rises, but that’s not entirely true. While hot air weighs less than cold air and will naturally rise, heat travels in all directions; from hot to cold. Heat flows between substances when there’s a difference in temperature. If you leave a 32°F ice cube sitting in a 69°F room, heat from the room will transfer into the ice causing it to melt. If both the ice cube and the room are both 32°F, no heat transfer will take place. Theoretically can extract heat from a substance until absolute zero, -459.67°F (−273.15°C) where all molecular motion would stop.