7 Things You Must Know Before Buying a Tankless Water Heater

Before you go out and buy that new tankless water heater there are a few things you should know, so that your family doesnt end up with cold water and you end up with a rising energy bill and the cold shoulder.

In this Tankless water heater buying guide, we will help you learn about things like what kind of fuel makes the most sense for your hot water heater, as well as several other factors like unit sizing, and location. We’ll also show you how to understand the effects of flow rate and determine how ground water can effect your tankless buying decision. By the time you finish, we hope you have the tools and knowledge to to making a better informed purchase.

Fuel or Energy Source

The first step in deciding what type of tankless heater you should use is to determine the fuel source. You need to decide between a electric style unit such as the Bosch Tankless Water Heater or the Titan Tankless line, or the gas powered models like the Rheem Tankless Water Heater as well as the Rinnai line of Tankless Heaters.

Tankless Unit Size, Location and Demand

You must determine what  your unit is expected to do. Is it going to be for heating one shower (single point usage), a entire bathroom (multi-point usage) or an entire house (whole house usage)? You should take a walk around your home and visualize where you could best put a tankless heater. Look in a bathroom and imagine where gas pipes, water pipes and electrical power will need to run. Would an electric model work best or can I get gas to that room? Do the same thing in the basement or mud room make a plan before you buy.

How to Determine Flow Rate

Next you will need to determine how many points of usage the unit will be required to provide for. Each faucet has its own flow rate requirement. Review the chart below to give you an idea of what different faucets in different parts of your home require.  You can learn more about flow rate and how to determine flow rate from your own faucet.  Flow Rate and Why Its Important.   The chart below is a handy guide to help you determine how much total GPM (gallon per minute) you need from your tankless heater.

  • Bathtub 2.0 – 4.o GPM
  • Shower 1.5 – 3.0 GPM
  • Kitchen Sink  1.0 – 1.5 GPM
  • Laundry Tub  2.5 – 3.0 GPM
  • Dish Washer  1.0 – 3.0 GPM

Effect of Ground Water Temperature

How to figure out your ground water temperature-To determine the actual water temperature you can purchase a reliable thermometer from your local hardware store. Open the cold water tap in the sink closest to your water meter or well. Let the cold water run for a couple of minutes before doing the test.  Next depending on the sensitivity of your thermometer hold it under the water flow for two minutes or longer if needed. Then read the results. Write this number on a scratch pad for later use. Its that easy you now know your ground water incoming water temperature. Ground water temperature is a very important number to know. Read more about Ground Water Temperature and its importance at  Ground Water Temperature.
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Understanding Temperature Rise

Now that you know the ground water temperature it is time to determine the required temperature rise. This is the difference between the incoming cold water temp and the temperature at the shower head, sink, or wherever you need hot water. Below are two examples of temperature rise based on gallons per minute flow.

The Titan SCR2N-100

Temperature Rise Chart (° Fahrenheit) above your ambient temperature

Flow Rate

1.0 GPM

1.5 GPM

2.0 GPM

2.5 GPM

3.0 GPM

3.5 GPM

4.0 GPM

Temp Rise









Tempra 24 Plus

Temperature Rise Chart (° Fahrenheit)

Flow Rate 1.0 GPM  1.5 GPM 2.0 GPM 2.5 GPM 3.0 GPM 3.5 GPM  4.0 GPM
Temp Rise 164° 109° 82° 66° 55° 47° 41°

You will notice in the above samples the comparison between flow rate and rise in temperature. This will help you decide how large a tankless heater you need or if you should consider smaller single unit models.

Buying a tankless water heater takes a little more homework then you standard tank model. If you take the time to ask the right questions and run a few simple tests on your home water supply you will find that you will have a fantastic continuous hot water supply and you can enjoy it more by knowing you are saving money and energy. And no cold shoulder from the family. Once you have your information gathered you might take a look at the Top Rated 2011 Tankless Heaters for more information about the best of the year tankless water heaters.

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