Tankless water heaters are one of the more recent developments in home water heating. They are far more efficient than traditional holding tank systems, with the potential for significant energy savings for homeowners with limited water needs.
However, most experts agree that even homeowners with larger water requirements can generate high energy savings when they install one unit for each hot-water outlet.
Understanding how tankless water heaters work can help you determine if a single unit or multiple applications will suit your hot water needs.
Flow Rates
There are two types of tankless water heaters: Electric and gas. Most electric water heaters deliver a flow rate, or the amount of hot water it can generate, between 2 to 3 gallons of hot water per minute, while gas units deliver double that amount.
To determine your hot water needs, you will need to calculate the maximum flow rate necessary. The best way to do this is to add the flow rates of all the home fixtures that might be used simultaneously. For instance, if one tankless water heater were to provide water for a shower and a dishwasher at the same time, the flow rate (even with a low flow showerhead) would exceed the capacity of an electric heater. In this case, two separate installations would generally be required to meet flow rate demands.
Temperature Rise
The temperature of the water as it comes out of a particular application is also critical. You see, the water coming into your home is set at a pre-determined temperature, usually 50 degrees. So, your tankless water heater will need to raise that temperature, depending on the application.
Typically, an appliance like a dishwasher or clothes washer requires hotter water, and a temperature rise of about 90 degrees. For all other applications, such as sinks and showers, a 70 degree temperature rise is adequate.
Selecting A System
It’s important to work with a professional to correctly size a tankless water heater for flow rates and temperature rise. In general, to utilize a tankless system for the entire home requires that several units are installed to accommodate your water heating needs.
For more expert advice about tankless water heaters and other issues related to home comfort, please contact us at T.F. O’Brien Cooling & Heating. Serving Long Island, we’re always happy to help.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about other HVAC topics, download our free Home Comfort Resource guide.
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