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Riddle: How does a hot water heater not waste energy? Answer: When it’s properly sized. The water heater -- or water heaters -- in your greater Cincinnati home should have the capacity to easily meet your home's high-demand-period needs yet operate efficiently without wasting energy -- or water.

Need sizing for a combination water/space heating system? See your HVAC contractor about your specific situation.

How to size your water heater
Tankless units are rated by the maximum temperature rise they can efficiently achieve at a certain water-flow rate. Calculate requirements for whole-house water heating and/or remote heating, such as for a bathroom in a guest house.

• Flow rate: Estimate how many hot water fixtures (sinks, showers, appliances) you expect to use at once, and total the flow rates in gallons per minute.
• Temperature rise: Subtract incoming water temperature from the necessary output temperature. A rule of thumb is to assume input water is about 50 degrees. Water heated to 120 degrees is normally fine for household use.

Continuous water heaters are generally capable of a range of input temperatures. A 70-degree rise can generally flow at a rate of 5 gpm with a natural gas on-demand water heater and 2 gpm with electric heating. Lower inlet temps and flow rates may put out cooler water at distant fixtures. It’s possible to adjust the output temperature via thermostat-controlled systems.

A solar water heater's storage capacity and collector area must efficiently handle at least 90 percent of a home’s summer hot-water requirements. Solar heating-system experts can take measurements to figure your system needs and size.

For storage tank and heat-pump heating, the first hour rating is key to determining the amount of hot water the heater can put out hourly. Select a unit with first-hour ratings that reach within 2 gallons of peak-hour needs.

Have questions about how to size your water heater? The professionals at Apollo Home Heating, Cooling and Plumbing are happy to help. Visit our website, or call us for solutions to your hot-water needs.

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