Hot water recirculation with a tankless heater

A tankless heater only fires when water flows, so the first gallon to a far tap is the cold water sitting in the pipe. A recirculation pump moves hot water back toward the heater on a timer or on demand, so it arrives faster. Some heaters have a pump built in; others take an add-on pump at the heater or under the far sink. Every tankless heater has a minimum flow to fire, so the pump and piping must follow the heater maker's recirculation instructions.