What is the best option for this situation?
Answer: 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 the third in line with a 50-gallon water heater.
The answer depends on whom you speak to. I have no preference either way, but our present "standing" heater doesn't seem to be a major expense, compared with the sump pump in the spring or basement dehumidifier in the summer.
There are differences of opinion among plumbers, who appear to favor conventional storage heaters, and the electric and gas on-demand manufacturers, who seem more interested in emphasizing the drawbacks to their competitors' products than in helping consumers.
A "neutral" source of information, the U.S. Department of Energy, says the following:
Demand water heaters heat water directly; they avoid the standby heat losses associated with storage water heaters.
When a hot water tap is turned on, cold water travels through a pipe into the unit. Either 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 with enough hot water. However, its output limits the flow rate.
Typically, demand water heaters provide hot water at a rate of two to five gallons per minute - those that are gas-fired produce 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 clothes washer or dishwasher.
