How To Size Your New Water Heater — Tankless Or Conventional

Before you purchase a new tankless or conventional water heater, you first need to determine the correct size to meet your hot water needs. An oversized water heater will use excess energy, and an undersized water heater will cause unnecessary deficiency of hot-water availability.

In a tankless system, estimate hot water usage by adding up the flow rates, or gallons per minute, of each hot water device you expect to use in your home at the same time. This will give you the total flow rate for the system. Flow rates for fixtures made after 1992 have been set by federal regulation to use no more than 2.2 gallons per minute. Installing low-flow aerators to your fixtures will reduce the water demand in your household, and are good way to not only save water, but save on energy costs associated with hot water usage.

After determining the total gallons per minute, or GPM, next determine the temperature rise, which is the difference in temperature from the incoming water and the hot water temperature you wish you use. For example, the most common temperature rise for most residential applications is 70 degrees, taken from a point-of-use temperature of 120 degrees minus an incoming water temperature of 50 degrees. Using the GMP and the temperature rise numbers, you can determine which tankless water heater will meet your home’s needs.

For sizing a conventional tank hot water system, estimate your peak hour demand, which is the hour of the day you expect to use the most hot water at once. This ensures that when demand is at its highest, the tank has enough hot water ready for distribution. For example, if you expect your family to take three showers and the dishwasher to run at the same time in the morning, the total gallons used in these activities would be your peak hour demand. The system you choose should be able to adequately serve your peak hour demand, in order to avoid hot water shortages.

For more information or questions about water-heater systems, installation or replacements, please contact Sobieski Air Conditioning.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). Sobieski serves Wilmington, Delaware and the surrounding areas. Visit our website to see our special offers and get started today!

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