Stiebel Eltron Tankless Water Heater Model Selector
Note: This chart indicates all of the models that would be appropriate for each region based on the average expected incoming water temperature in the winter months and a desired flow rate of roughly 3 gallons per minute (GPM). Where multiple models are listed as appropriate, selecting a larger model will provided higher flow rates for more demanding applications. Your incoming water temperatures may differ from those assumed by this chart depending on your water source, location, season, and climate. To confirm your model selection, please measure your required flow rate and incoming water temperature, and compare to the maximum flow rate chart futher down this page.
|Flow Rate in
GPM at 60 PSI
|Typical Shower||1.5 to 2.0 GPM (Max. 2.5 GPM)|
|Typical Bath Tub Faucet||2.0 to 3.0 GPM|
|Bathroom Vanity Sink Faucet||0.5 to 1.5 GPM|
|Kitchen Sink Faucet||1.0 to 2.2 GPM|
|Clothes Washer||1.5 to 3.0 GPM|
Determining which model of Stiebel Eltron Tankless Water Heater will work best for your application is based on 3 factors:
- your incoming water temperature
- the maximum flow rate you desired
- desired features
- the electrical service available
Incoming Water Temperature
In general, the colder the incoming water temperature is in your region, the more powerful your tankless water heater needs to be to heat the water to your desired temperature.
We have created a handy map and chart (on the right) to help you select the an appropriate tankless water heater model based on the average expected winter incoming water temperatures in each climate region in North America, an output water temperature of at least 105 degrees F (hot enough for all domestic applications), and a water flow rate of at roughly 3 gallons per minute or more. If more than model is listed for your climate zone, you can select one of the larger models for more demanding applications with desired flow rates greater than 3 gallons per minute. Also, keep in mind that the incoming water temperature in your area may vary depending on your water source, location, elevation, and season. You will also need to confirm that your home has enough electrical service to support the selected model - see below.
Maximum Flow Rate Required
Determining your home's flow rate requirement is a simple task and can aid greatly in sizing a tankless water heater to your application. Most families and small businesses will only demand one major hot water use at a time (shower, bath, etc.) as the water pressure typically makes it difficult to run multiple high-flow applications at the same time. Accordingly, a maximum flow rate of about 3 gallons per minute (GPM) is sufficient for most residential applications. The chart to the right will give you some guidelines as to the flow rates of common water demands. It is important to note that the flow rates of these applications will vary due to water pressure and other factors. Accordingly, you are encouraged to test you actual flow rates in your home for a more precise model determination. To calculate the exact flow rate of each application in your home:
1. turn on the faucet and time with a watch how long it takes to fill a one gallon container (in seconds)
2. divide 60 by the number of seconds it took to fill the 1 gallon container - ex. a shower that takes 40 seconds to fill a one gallon container has a flow rate of: 60 divided by 40 seconds = 1.5 gallons per minute
Repeat for other faucets, showers, and applications in the home or business.
You can use the results to determine what applications you will be able to run simultaneously (at the same time) based on the maximum output of each model as per the chart below. In warmer climates, it is possible to use one of Stiebel Eltron's more powerful models (Tempra 24, 29 & 36) to run flow rates of up to 8 gallons per minute and still achieve a comfortable output temperature suitable for a shower or virtually all other domestic needs. However, in northern climates, your flow rate expectations should be significantly lower (up to 3.5 to 4.0 GPM), depending on your incoming water temperature.
If your flow rate desires exceed the capabilities of the largest model, you may still find it desirable to "go tankless" to obtain the other benefits of tankless water heating (save energy and operating cost, save space, etc.), however, you will have to adapt your water usage to meet the flow capacity of the heater. Fortunately, the vast majority of homeowners and businesses can be fully accommodated by an appropriately-sized tankless water heater. If you are in doubt, please give us a call and we will help you evaluate whether a tankless water heater is a good choice for your application, and help you select an appropriate model. For large demands, you may also be able to install more than one heater in series or parallel or create 2 separate water heating zones and supply each with its own heater.
The following chart illustrates the maximum flow rate that can be achieved with each model based on a 105F output temperature (240 volt power input). If your home or business has less than 240 volt power (208v for instance), your maximum flow rate will be lower. Please download the Stiebel Eltron Tempra Brochure for maximum flow rates based on 208v input) Note, most people shower or bathe at a temperature of between 98 and 104F.
Simply look up your incoming winter water temperature (color-coded based on the map above) and desired flow rate to determine your model recommendation. Don't forget that incoming water temperature may change throughout the year depending on the season. You can expect significantly higher flow rates during the summer months in most regions due to the warmer incoming water temperature.
|Incoming Water Temperature|
|Tempra 36 /
Tempra 36 Plus
|3.8 GPM||4.1 GPM||4.5 GPM||4.9 GPM||5.4 GPM||6.1 GPM||7.0 GPM||8.2 GPM||9.8 GPM|
|Tempra 29 /
Tempra 29 Plus
|3.0 GPM||3.3 GPM||3.6 GPM||3.9 GPM||4.4 GPM||4.9 GPM||5.6 GPM||6.5 GPM||7.8 GPM|
|Tempra 24 /
Tempra 24 Plus
|2.5 GPM||2.7 GPM||3.0 GPM||3.3 GPM||3.6 GPM||4.1 GPM||4.7 GPM||5.4 GPM||6.5 GPM|
|Tempra 20 /
Tempra 20 Plus
|2.0 GPM||2.2 GPM||2.4 GPM||2.6 GPM||2.9 GPM||3.3 GPM||3.7 GPM||4.4 GPM||5.2 GPM|
|Tempra 15 /
Tempra 15 Plus
|1.5 GPM||1.6 GPM||1.8 GPM||2.0 GPM||2.2 GPM||2.4 GPM||2.8 GPM||3.3 GPM||3.9 GPM|
|Tempra 12 /
Tempra 12 Plus
|1.3 GPM||1.4 GPM||1.5 GPM||1.6 GPM||1.8 GPM||2.0 GPM||2.3 GPM||2.7 GPM||3.3 GPM|
|Suitable only for small point-of-use applications (a single sink for instance).|
|Suitable for homes with modest hot water needs and that use flow restricted showerheads. Very careful measurement of your actual water flow rate and incoming water temperature is recommended before making a final model determination. Please call us for assistance if you are unsure.|
|Best model choices for general whole-house water heating demands. Areas indicating a maximum flow rate of 4.0 gallons per minute or more are generally satisfactory for running 2 showers at a time with standard showerheads.|
Stiebel Eltron currently offers two Series of Tempra tankless water heaters, the standard Tempra series and the Tempra Plus series. The primary difference between the 2 lines is that the Tempra Plus models feature Stiebel Eltron's exclusive Advanced Flow Control technology. This technology automatically adjusts the flow of water if the unit's sensor's detect that the flow demand is exceeding the heater's capacity at the current temperature setting. This feature is especially useful in colder climates and applications where the electrical service is not large enough to permit the installation of a larger model. It is also desirable where high output temperatures are required for temperature critical applications (commercial dishwashers, etc.) where flow rates are not always predictable and maintaining a temperature is more important than maintaining flow rate.
All Tempra Plus Series models also feature a full digital temperature setting display. This features is currently available only on certain Tempra Series models (see models specifications for details).
Choosing which option is best for your needs is largely only a choice of personal preference and budget. Either model series is satisfactory for general residential applications.
Available Electrical Service
Your final consideration when choosing a model of Stiebel Eltron tankless water heater is the availability of suitable electrical power to service your water heater. All models of the Stiebel Eltron tankless water heater require single phase 208 to 240 volt power. Since an electric tankless water heater works entirely on demand, it must transfer a massive amount of energy instantaneously to the water. Accordingly, tankless water heaters have a high peak electrical load even though they will substantially reduce your overall electricity consumption. Consideration must be given to the number of AMPS of electrical service your home has to support the operation of the heater and other concurrent electrical needs. While most homes have enough power to accommodate a whole-house electric tankless water heater, some do not (even some newer homes do not have enough power). We highly recommend that you confirm that your home or business has enough power capacity before you make any final decisions regarding model selection. It is easy to do and could help avoid disappointment or unexpected installation costs.