Does An Electric Tankless Water Heater Make Sense?

David Voros owns a vacation home that isn’t used frequently, but every so often the house sees a lot of guests. What, he asks, is the best way of providing enough hot water for a crowd?

Voros sketches out these parameters in a recent Q&A post: very cold incoming water temperatures, a limited amount of space for a tank-style heater, and limited availability of gas. The house has photovoltaic panels, and Voros would like to avoid running another exhaust pipe through the building envelope.

For all of those reasons, he’s drawn to an electric tankless water heater. Whether that’s a good idea is the basis for this Q&A Spotlight.

Electric models need a lot of juice

The cost of operating a tankless water heater won’t be any more expensive than operating a tank-style heater, GBA Editor Martin Holladay says, but a tankless model will need an oversized electric service, and that can be expensive to install.

“There are also disadvantages for the local electric utility, since it has to provide high-current electricity in short bursts,” he adds, “but you may not care about that.”

Dana Dorsett adds some particulars: a whole-house tankless draws more than 25,000 watts of electricity and needs a 150-amp, 240-volt breaker. The total electrical service for many houses is less than that, he adds. A typical tank-style water heater draws less than 5,000 watts, and it will have relatively low standby losses. And when Voros is away, a tank-style heater can simply be turned off.

Dorsett also points out some of the potential rate implications for Voros, who is a solar customer.

“In many locations, utilities are struggling to recover their infrastructure costs, particularly on low-use or net-zero electricity houses with solar,” he says. “The concept of applying ‘demand charges’…

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