If for no other reason, the heat in the pipe will rise to the highest point and that is probably the roof.
Heat does not rise! Heat travels from high temperature to low temperature. Gravity is not involved! Hot air rises because the denser cold air is pulled down by gravity. If the roof was colder than the building, would the cold fall to breaker panel? RANT OFF
Sorry, thermodynamics and nuclear power are triggers for over explinations.