How to determine what size tankless water heater you need

For a home with 1 bathroom, we recommend 6-7 GPM; 2 bathrooms, 8 – 9 GPM; and 3+ bathrooms, 9-11 GPM. In our experience, smaller 4-5 GPM units are suitable for studio apartments and small one bathroom homes or other application specific needs.

Comparing a 3.2 GPM tankless water heater to a forty gallon tank type heater is possible. For example, if a tankless unit produces hot water at 3.2 gallons per minute, this rate of flow will run a 40 gallon tank type heater out of water in only ten minutes. Tankless heaters do not store water.

There are two factors that need to be considered when sizing a tankless water heater: Flow Rate (GPM): How much hot water you will need at any given time. Temperature Rise (ΔT): The difference between the incoming cold water temperature and the desired temperature.