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Choosing the right Tankless Electric Water Heater for your home.

Choosing the right Tankless Electric Water Heater for your home.

In deciding on a Tankless Electric Water Heater there are three main factors.

1) First is determining what application/install you are going to use the unit for.
For most instances:

180 °F – “High temperature sanitizing” commercial dishwashers
140 °F – “Low temperature” commercial dishwashers
120 °F – Residential Whole House Tank Replacements; Commercial kitchen sinks including 3-compartment sinks
105 °F – All point of use handwashing including public handwashing; Standard shower temperature
60 °F to 90°F – Safety showers and eyewashes. Consult your Safety Engineer for a specific temperature.

2) Find what your incoming water temperature is for your state. This varies and is an important step in making sure you purchase the correct unit. The below map reflects general water temperatures

Now subtract step one from step two.


Tankless Electric Water Heater


If you are trying to reach 105 degrees for handwashing and you live in Nebraska with an average incoming water temp of 47. You will need a unit that will allow for a TEMPERATURE RISE* of 58 degrees.

105 - 47 = 58 degrees

(Temperature Rise means the total temp needed to heat the water to your desired temperature)

3) Determine total gallons per minute (GPM) needed for your application:

List the number of hot water devices you expect to use at any one time. Then, add up their flow rates (gallons per minute). This is the desired flow rate you'll want for the demand water heater. 


Bathroom Faucet  0.5 - 1.5 GPM

Low Flow Kitchen Faucet 1.0 - 2.5 GPM

Shower  1.5 - 2.0 GPM

Bathtub 4.0 -  Higher GPM

Dishwasher 1.5 - 3.0 GPM

Washing Machine 1.5 - 3.0 GPM


For our purposes we are going to use the previous Temperature Rise of 58 degrees.
We will be using this for a point of use on a Bathroom faucet using 1 GPM.



Each Brand may require different power needed to operate at this level.
For ONE Bathroom Faucet using 1.0 GPM and needing to reach 58 degrees. Find the 1.0 GPM column and follow it down to the closest 58 degree temperature.


See the examples below per brand.


SR-40/208 or the SR-30/277 

Tankless Electric Water Heater


SPEX8208 or SPEX75

Tankless Electric Water Heater





Tankless Electric Water Heater



If it will not produce the desired flow rate and temperature rise to get to a comfortable hot water handwashing temp. of 105°F, then choose another model with more kW and amps, and ensure that you can supply it with the required electrical capacity

It is acceptable to use estimates or approximations for water temperature and flow rates. However, the more accurate the calculation, the better the performance of your tankless electric water heater in operation.

Under sizing your heater will cause no hot water or shortages during peak demand times; oversizing will result in unnecessary heater purchase expense and excessive installation costs


Related Articles:

Choosing the Right Rheem R-TEX Electric Tankless Water Heater


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