How To Choose a Tankless Water Heater

Written by: Erica Spangler
Design Specialist
(800) 375-3403

Tankless Water Heaters create water on demand, so you’ll never run out of hot water. Check out the many tankless water heater options and features available when you are ready to make the switch to energy and space efficiency.

How a Tankless Water Heater Works

Hot a Tankless Water Heater Works
  1. Turn on the hot faucet or start your laundry and the tankless water heater instantly creates hot water.
  2. The incoming water temperature determines how much heat is needed to reach your desired temperature.
  3. When you turn off your faucet or the laundry is completed, the tankless water heater shuts off.

Benefits of a Tankless Water Heater

Tankless Water Heater Saving Benefits

40% Decrease in Utility Costs

Tankless Water Heater Energy Benefits

Energy Efficient – ENERGY STAR Options

Tankless Water Heater Heats Faster Benefit

Faster & Unlimited Hot Water

Tankless Water Heater Smaller in Size

Smaller Than Standard Hot Water Heaters

Fuel Type

Electric Tankless Water Heater


  • Uses an electric power source
  • Each tankless water heater has an unique electrical requirement
  • Has a lower output and a higher use of electricity

Generally, they can only supply one major application at one time. Consult an electrician before purchasing.

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Gas Tankless Water Heater


  • Requires a gas line and a supply of either natural gas or propane
  • Can supply more hot water and more applications

Gas can be installed indoors or outdoors, but, generally work better indoors in very cold climates.

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Make sure to select the correct tankless water heater based upon your gas source whether it is natural gas or propane. A solar powered pump is also an option for an alternative energy source.

Important Considerations

Ground Temperature Infographic

Ambient Ground Water Temperature

  • Average temperature of your ground water
  • Necessary to determine how much your ground temperature must rise to reach the desired hot temperature

You will notice that many tankless hot water heaters list performance data that notes the flow rate, or gallons per minute (GPM), to temperature raise ration. Make sure to know your ambient water temperature so you can choose the correct tankless water heater for ideal water temperature.

Practical Flow Rate

  • Determines how the tankless water heater will raise the water’s temperature
  • Continuously outputs water, measured in GPM

Condensing vs. Non-condensing


  • Recovers more than 85% of the gas than a regular tankless water heater would typically vent out
  • The warm exhaust gases transfer to the incoming water preheating it before the primary heat source

These are usually more affordable and tend to use fewer components. Condensing reuses the steam so it can be vented through pvc piping.


  • Units do not make use of the lost heat
  • Heat is vented out

These units require a special vent and the condensate created must be handled. The non-condensing units are typically more expensive and require additional components. These push gas through stainless steel piping outside.


Use this table to determine which size tankless water heater you need:
Tankless Water Heater Power Table
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