Why there is a wait at all
A tankless water heater stores nothing, so when a tap opens the unit fires and heats water that then has to travel through the pipe to the fixture. The wait is the travel time for the cold water already sitting in the line to clear. A storage tank has the same travel time on a long run; its advantage is that the water in the pipe was heated earlier, not that it arrives faster.
Recirculation attacks the travel time, not the heater. It keeps warm water moving through the line so that a tap opens onto warm water sooner. It does not make hot water unlimited, and it does not change the winter flow limits of a tankless unit.
The two plumbing arrangements
The traditional loop uses a dedicated return line from the farthest fixture back to the heater, with a pump moving water around it. It works well but needs pipe that a finished house may not have.
Where a return line cannot be run, a crossover valve at the farthest fixture connects the hot and cold lines under the sink so the pump can push water through the cold line back to the heater. This is easier to retrofit but depends on the fixture's plumbing and needs the valve installed correctly, with the relevant check or code requirements respected. Either arrangement is a plumbing change, priced as part of the installation.
Tankless recirculation
Tankless units approach recirculation in two ways. Some have a built-in pump and internal logic: Navien's NPE-A2 series publishes a recirculation feature with the pump inside the unit, so the loop needs the return path but not a separate pump on the floor. Others use an external pump controlled by the unit or by its own timer.
Rinnai documents recirculation on its condensing tankless series and reserves a diagnostic code for recirculation-related faults, which is one reason the loop is commissioned and tested rather than left to chance. Whichever arrangement is used, the unit needs a return path and the controls need to be set so the pump is not running around the clock.
Controls and the honest cost
Recirculation controls fall into three families: a timer that runs the pump at set hours, a temperature control that keeps the loop warm, and an on-demand control that starts the pump only when someone calls for hot water. The choice decides the gas use. A timer set for the morning and evening peaks costs far less to run than a temperature control holding the loop warm all day.
A recirculation loop is not a saving. It trades gas for convenience, and the estimator on this site itemizes it as an adder rather than folding it into the base price, so the cost of the loop is visible before the work is approved.
When recirculation is worth it
Recirculation earns its place when the wait is long and frequent: an ensuite at the far end of a large house, a kitchen far from the mechanical room, or a home where several taps are used through the day. On a short run, or where the heater is central, the wait may be a few seconds and the loop adds equipment and gas use for little gain.
The honest answer at an assessment is to measure the run and the actual wait before recommending a loop. Where the wait is caused by a fixture or a blocked line rather than distance, the fix is different, and the diagnosis comes before the equipment.
What CANRO does
CANRO Heating & Cooling assesses recirculation as part of a tankless installation or conversion, and publishes hot-water recirculation among its services. Whether a specific home suits a dedicated return line, a crossover valve or a built-in-pump unit is decided at the assessment, because it depends on the plumbing that already exists.
Written estimates for installations are free, and the recirculation allowance is shown separately so it can be accepted or declined on its own.