An easy free solution. Turn on all the sink hot faucets and the shower in the bathroom. In 30 Sec you get hot water. Turn off the sinks and step in the shower. The tankless systems have a low and a high demand heat setting. With only the shower running it will be in low demand and take about 2 minutes to get hot water. With the sinks on, it will be in high demand. With flow restrictors, its probably a gallon of water in either case.
Some people remove the flow restrictors which has the same effect as shifting the heater into high demand from what I hear.
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