How Do I Select a Tankless High-Efficiency Water Heater?

High-efficiency tankless water heaters can provide an endless stream of hot water.

High-efficiency tankless water heaters can provide an endless stream of hot water.

When it's time to select a water heater, high-efficiency tankless systems offer some obvious advantages: an endless stream of hot water, energy efficient operation and equipment that outlasts conventional units by many years. Before you can decide which make or model fits your budget, it's important to first assess how your household uses hot water, and then determine how the different types of tankless systems might best meet your family's needs.

How Tankless Water Heaters Work

As soon as you turn on the hot water, a flow sensor kicks the tankless water heater into action. Its burner sends up to 200,000 BTU of heat to a heat exchanger, which instantly increases the water's temperature as much as 77 degrees. A larger tankless unit can supply up to 4 gallons of 120-degree water per minute, which should be sufficient for feeding one or more WaterSense showerheads, or operating the dishwasher and washing machine at the same time (See Reference 1, 2).

Whole-House Gas Tankless Water Heaters

The most important consideration in selecting a whole-house tankless unit is its capacity in gallons per minute (gpm). A shower will use between 1.5 to 2.5 gpm of hot water, the kitchen faucet may use a similar amount, a dishwasher will consume about 1.3 gpm and the clothes washing machine about 3.5 gpm. It's important to select a tankless unit that can supply enough hot water to meet a household's expected use. A family of two would probably find a small capacity high efficiency tankless water heater sufficient if they are willing to schedule their showers and appliance use for different times. A larger family might prefer larger capacity Energy Star unit that would allow two showers to operate at once (See Reference 2).

Electric Water Heaters

While there are whole-house electric tankless water heaters, the most common application for high-efficiency electric models is for point-of-use installation under a kitchen or bathroom sink. These units provide hot water instantly and are ideal for room additions or outbuildings such as living quarters above a garage space. A 2.0 gpm model can supply a bathroom sink and a shower that's fitted with a 1.5 gpm showerhead, or handle the needs of a kitchen sink and dishwasher (See Reference 3, Page 2.2),

Tankless Tax Rebates

Tankless water heaters have a higher initial cost that conventional water heaters, but there may be tax incentives in your area for installing a high-efficiency, energy saving model. In Oregon, for instance, homeowners may qualify for a 25 percent tax credit against the price of a tankless water heater that is at least 82 percent efficient. In some communities, your local energy company may offer rebates that lower your utility bill when you purchase and install selected high-efficiency water heaters (See Reference 4).


About the Author

Mike Matthews is editor of Green Building Product News, a national publication that covers sustainable innovations in building and remodeling, and he has spoken at national conferences on green building. He has also served as founding editor of "Paint Dealer" magazine.

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