Selecting The Right Size Tankless Water Heater

Selecting The Right Size Tankless Water Heater

Tankless water heaters, also known as on-demand water heaters, are increasingly become more and more popular. A tankless water heater only heats water that is needed and does so quickly.

If you’re like many homeowners, you’re probably thinking of making the switch from a traditional water heater to a tankless water heater.

Step One

To start, figure out the estimated flow rate and temperature rise you’ll need. There’s a big difference between providing heating water to a whole home vs. just a single bathroom.]

Figure out how many appliances and fixtures you’ll want to run and their total flow rate.

Finally, add up their flow rates, using gallons per minute. This will determine the flow rate you’ll want for your tankless water heater.

Tankless Water Heater Flow Rates

How much hot water do you use at any one time? It’s highly unlikely that you’ll be running multiple showers at once. A shower and at least one sink is more realistic. Here’s a quick depiction of different fixtures and their range of water usage and average water temperatures:


  • Tub: 4.0 GPM, 102 degrees Fahrenheit
  • Shower: 2.5-3.0 GPM, 104 degrees Fahrenheit
  • Washing Machine: 2.0 GPM, 120 degrees Fahrenheit
  • Dishwasher: 1.5 GPM, 110 degrees Fahrenheit
  • Kitchen Sink: 1.5 GPM, 110 degrees Fahrenheit

Step Two

Make sure to calculate temperature rise. Subtract the incoming water temperature from the desired temperature you want from your fixtures.

Most people will want their water heated to about 105-115 degrees Fahrenheit. On the low end, you’ll need a tankless water heater that produces a temperature rise of 55 degrees Fahrenheit.

For help finding the right tankless water heater for your needs, contact A-Abel for help and a free estimate.