Installing a Tankless Water Heater? Make Sure It’s Sized Right

There are a few different names for tankless water heaters, including “demand water heaters,” but their chief feature is right in the name – they do not require a tank to ensure a continuous supply of hot water in the home. As a matter of fact, the tankless characteristic is its main advantage. Since they heat water instantly, there’s no hot water tank that ever runs out, even after the three teenagers each take a shower right after the other one. If you’re looking to replace your water heater, tankless just might be the way to go.

How to Size a Tankless Water Heater

Since tankless water heaters are rated by the maximum possible temperature increase at a certain flow rate through the unit, it will be necessary to determine the flow rate and the temperature increase for the water-heating application you have in mind. Then follow the steps below:Tankless Water Heater Installation Planned? Make Sure It's Sized Right

  • List your hot water-using devices and their gallons-per-minute flow rate. The flow rate through your tankless water heater should be greater than the total of these devices’ flow rates. If you have three hot water uses that each requires a flow rate of 1.5 gallons per minute, the total flow rate needed is 4.5 gallons per minute.
  • To calculate the temperature increase, subtract the water temperature input to the heater (basically tap water temperature) from the desired output temperature. The default incoming is 50 degrees, and the normal desired output is 120 degrees. For example, if you needed your 50-degree water heated to 140 degrees on the output side, you would need a water heater capable of generating a 90 degree temperature increase.
  • In the home example from above, you have determined that you need a tankless water heater that can handle a flow rate of roughly 5 gallons per minute, and produce a 90 degree temperature increase.

Contact Us

At Geisel Heating, Air Conditioning and Plumbing, we’ve been serving Northeast Ohio for more than 75 years, and we’ll be glad to help with any home comfort issues you might have. Please contact us to discuss your concerns.

Our goal is to help educate our customers in Cleveland, Ohio about energy and home comfort issues (specific to HVAC systems).  For more information about tankless water heaters and other HVAC topics, download our free Home Comfort Resource guide.

For those Do it Yourselfers who would rather take control of your own indoor comfort, you can shop our online store for replacement parts, products and accessories!

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