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Q: We are ready to gut our children's bathroom. They are getting to the ages where they'll be showering more often, and our 80-gallon electric water heater isn't enough to allow for five showers in a row. We are considering a separate hot water source for their shower.

I've read about instant heaters, but a plumber recommended we get a second 80-gallon tank, which I think is overkill and would be too expensive.

We have been told the electric tank-less models aren't satisfactory performers. We do have propane for our fireplace and grill, so that's an option.

What is the best option?

A: I'm not sure any system - conventional or on-demand, gas or electric - will be able to provide enough hot water for five showers in a row, but that's just the skeptic in me, since I'm usually third in line with a 50-gallon water heater.

There are differences of opinion among plumbers, who appear to favor conventional storage heaters, and the electric and gas on-demand manufacturers. A "neutral" source of information, the Department of Energy, says:

Demand water heaters heat water directly; they avoid the standby heat losses of storage water heaters.

When a hot water tap is turned on, cold water travels through a pipe into the unit where a gas burner or an electric element heats the water. With a demand water heater, you don't need to wait for a storage tank to fill up. However, its output limits the flow rate.

Typically, demand water heaters provide hot water at a rate of 2 to 5 gallons per minute; gas-fired ones have higher flow rates than electric ones. Yet even the largest gas-fired model cannot supply enough hot water for simultaneous, multiple uses in large households.

To overcome this problem, you can install two or more demand water heaters, connected in parallel for simultaneous demands of hot water. You can also install separate demand water heaters for appliances, such as a dishwasher.

For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24 to 34 percent more energy efficient than conventional storage-tank water heaters. They can be 8 to 14 percent more energy efficient for homes that use about 86 gallons per day.

You can achieve even greater energy savings, 27 to 50 percent, if you install a demand water heater at each hot water outlet.

Send questions to Alan J. Heavens at Volume prohibits individual replies.