 This specialized type of tee fitting is used primarily in pressurized hydronic heating systems, to divert a portion of the flow from the main line into a side branch connected to a radiator or heat exchanger.The diverter tee is designed to allow flow to continue in the main line, even when the side branch is shut down and not calling for heat.Diverter tees have directional markings which must be heeded; a tee installed backwards will function very poorly.