Eemab #Eemax IFR 3-4 Inline Flow Restrictor 3/4'' Connections Supplied with 2.0, 3.0, 4.0 and 5.0 Gpm Insert, This insures optimal temperature output and Overall performance Installed on the outlet connection of the tankless water heater Limits the maximum volume coming out of the unit to a specified flow rate Prevents the exit temperature from cooling to quickly