High Flow Showerhead:3.0--4.0gpm

Dishwasher:1.0--2.5gpm

Laundry Machine: 1.5--2.5gpm

Well You need to convert this into gallons per minute to find the right size water heater to you. Although water heaters that have lower circulation rates are generally much cheaper, I would not advise cutting any corners when it comes to choosing size. The water can move from warm to cold and will not remain at a constant temperature if the water heater is too small. On the graph above I've supplied a general idea of the flow rate in gallons per minute that the normal household appliances use. This should only be used as a manual; real usage could vary for your house. Just add up the maximum gpm you will need at once and you are going to have the size of the tankless water heater you need for your dwelling.

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