Abstract: A valve for controlling temperature and for water balancing in a zone in a water based heating/cooling system. The valve comprises a housing having a water inlet port and a water outlet port. An internal wall with an opening is positioned between the ports so that when the opening is closed, water flow through the housing from the inlet port to the outlet port is prevented. A plug having predetermined flow rate characteristics is releasably secured in a receptacle in the housing. The plug is constructed and positioned to move with respect to the opening, between open and closed positions, respectively permitting and preventing the flow of water through the housing. A pressure tap is positioned in the housing on the inlet port side of the wall and another pressure tap is positioned in the housing on the outlet side of the wall. The taps, during operation of the valve, permit a determination of the pressure differential between the inlet port and outlet port when the valve is in open position.