Step 1: Maximum GPM Flow Rate Desired:
Step 1. How many hot water application would you like run at one time? Look at the chart to the right for the applications that call for hot water and much water they use per minute or ( GPM) , base on the applications you plan on running at one time your water heater must heat that much water per minute.
For example 2 showers, an average shower will produce 1.6 -2 GPM of water each minute. So you would need a tankless water heater that can handle 4 GPM of hot water every minute if you plan on running two showers at once )
Once you have gone over step 2 and 3 you may find you will not have enough power to run two or three applications at once. As a Tempra 24 owner in the winter we can only do 1 shower or 2 bathroom sinks at one time
Step 2: Incoming water temperature & temperature rise
Step 2: Identify the temperature rise needed to produce enough hot water. (Average Hot Water Temp is 105F-115 F )Look at the color chart of North America to find the average winter incoming water temperature in your region. Then identify how hot you want your water to come out of your shower. To get your temperature rise take your desired hot water temp minus the incoming water temp = temp rise.
Example 55 °F entering water 105 °F hot water temperature 110-50= 55 °F degree temperature rise
Step 2A : Temp Rise & Max GPM Chart
The following chart illustrates the maximum flow rate that can be achieved based on temperate rise. step 1 &2
This chart is based on a 240 volt voltage (Not 208 v) and the suggested electrical serviced needed to support the water heater (if you don’t have suggest power in show in step 3, step 2A chart not valued)