Sizing A Tankless Water Heater? Best Understand Flow Rate And Temperature Rise

Tankless water heaters are quickly earning an excellent reputation for providing continuous, convenient hot-water flow, nice energy savings, life spans nearly double of storage heaters and great flexibility in installation locations.

Before sizing a tankless water heater, it’s good to know its basic operation. Tankless water heaters deliver hot water on demand by heating water as it’s pumped through the unit en route to the hot-water outlet. There is no storage tank, which accounts for its high efficiency — up to 50 percent over storage-tank water heaters. Whole-house tankless systems utilize electricity or gas burners for heating water. Smaller electric-heated units can be located near hot-water outlets.

Sizing A Tankless Water Heater

There are many variables for sizing a tankless water heater, including flow rate, temperature rise, heating source compatibility and your specific preferences for energy efficiency, fast hot-water supply and installation location and costs. Two primary factors make clearer the overall interaction of variables: flow rate and temperature rise.

  • The flow rate of a water outlet is the gallons per minute (GPM) supplied. The flow rate for an entire household is the maximum GPM used at one time. For tankless water heaters, the flow rate is GPM of hot water supplied in relation to temperature rise.
  • Temperature rise is the total degrees by which incoming water must be heated to reach the desired hot-water temperature. For instance, if your incoming water temperature is 58 degrees, and your desired hot-water temperature is 120 degrees, your temperature rise is 62 degrees.

Once you’ve determined flow rates and temperature rise, you design a tankless system specific to your home and needs. For instance, if you’ve decided that energy efficiency and quick hot-water supply are most important, you would want a series of smaller tankless units installed near the hot-water outlets. If you have a smaller household that uses less water, then you might go with one whole-house tankless unit for cheaper installation.

By working closely with a heating and cooling professional, you’ll have an efficient tankless system to meet your needs. Contact us at Overland Park Heating & Cooling today.

Our goal is to help educate our customers 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.

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