A tankless water heating system, also sometimes referred to as a demand or instantaneous system, is often a more economical choice when compared to a standard storage tank style water heater. Sizing a tankless water heater system will help you determine the number of tankless heaters you will need to maintain the same water heating capacity that you’re currently receiving from your traditional system.

Tankless water heaters are rated by the maximum temperature rise that can be delivered for a given flow rate. Most municipal and well-based water systems start with a water temperature of about 50 degrees. To reach a temperature of 120 degrees (the typical temperature coming out of a hot water tap), there would need to be a 70-degree temperature rise. Most gas-fired tankless heaters can deliver a temperature rise of 70 degrees at a flow rate of 5 gallons per minute, while electric heaters can deliver this temperature at a rate of 2 gallons per minute. A higher temperature rise can be attained by lowering the flow rate or using additional heaters on the same line.

To calculate your needs, the first step is determining the maximum flow rate that your system will have. If you intend to run multiple hot water outlets at the same time, you will need to calculate the total flow rate from each fixture you intend to use and then add them together. For example, if you have a shower head that uses 3 gallons of water per minute and a sink faucet that uses .75 gallons per minute, your system will demand 3.75 gallons of hot water per minute. A single electric tankless heater may not suffice, and adding low-flow fixtures might also be suggested.

For help determining whether tankless water heaters are right for your home or for tips on sizing a tankless water heater, contact the pros at Stack Heating & Cooling. We’ve proudly served homeowners throughout greater Cleveland since 1976.

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.

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