In practical terms, the amount of hot water produced by tankless water heaters will vary with incoming water temperatures.

Incoming water temperature is an important, but frequently overlooked, variable in the sizing of a tankless water heater.

Ultimately, customer satisfaction with any type of water heater depends on proper sizing: making certain there is an adequate supply of hot water to meet not just one or two, but all the various needs of a given application - residential or commercial.