When a hot water tap is turned on, cold water flows through the tankless hot water system. The water passes through pipes inside of the system that are heated electrically or by gas burners. Although the hot water won't run out, the flow rate might be a bit limited. Tankless water heaters normally deliver hot water around a rate of two (2) to five (5) gallons per minute. Electric models tend to not have as good of a flow rate as the gas versions.
