The point is that the pipe is never full, because the waste water runs down the walls. Nothing's going to settle in a vertical pipe. When the pipe leaves the h

The point is that the pipe is never full, because the waste water runs down the walls. Nothing's going to settle in a vertical pipe. When the pipe leaves the heat exchanger and goes back to wiggling around the building on the way to the sewer, then sure, go back to sizing pipes based on thinking about settlement and other things.