All of the hot water radiators on the second floor of our house (1929 construction) have a valve, then a tee on the same side of the radiator. The water comes in from the vale, through a center passage of the tee and into the radiator. I assume the cold water is then forced out through the outer passage of the tee and down the return pipe. Is this an old type of monoflow tee? Does anyone know why are the second floor radiators like this, and the first floor ones have a feed pipe on one side and return pipe on the other?