Like the metric system, soccer and Capri pants for men, tankless hot water systems have never been fully embraced in the United States despite decades of popular usage in Europe and Asia.
For those not familiar with tankless hot water units, they heat up water on demand, as opposed to a hot water tank, which constantly heats up water even when it's not being used. Because tankless units just heat up incoming water, they can supply an endless amount of hot water, whereas hot water tanks can run of hot water temporarily.
If you are intrigued by the idea of endless hot water but aren't quite ready to ditch the hot water tank, Eternal by Grand Hall gives you the best of both worlds. A hybrid hot water heater, Eternal is primarily a tankless unit, but it also has a small hot water tank built into it.
At the 2008 Builders' Show I talked with Paul Home, product manager from Eternal, who explained to me that Eternal's small hot water tank preheats water so that the tankless system doesn't have to expend as much energy heating the water to your desired temperature. And this allows the Eternal to provide consistent and high water pressure (the reason for this is because the more a tankless unit has to raise the temperature of water, the less water pressure you'll receive).
I also spoke with a tankless hot water representative from Takagi who-not surprisingly-seemed quite confident that we'll be seeing more and more U.S. homes with tankless units. He noted that today's tankless systems are able to provide the amount of water pressure the U.S. market demands, and that it is consumers — not builders — who are getting educated and getting intrigued by what these units offer. (Note about water pressure from tankless units: Most provide between 2.5 gallons per minute (gpm) to 10 gpm, which is enough for most people's needs, but not everyone's.)
Besides the endless hot water tankless units provide, they are considered a green product because they are more efficient than most hot water tanks. This can save you money on heating costs in the long run, although the initial cost of a tankless unit can be twice as much as a standard hot water tank.
And this could be the bottom line when it comes to tankless hot water in the U.S.: Despite its advantages, the initial cost of tankless units will make plenty of people opt for the less expensive hot water tanks we've always used. When the price is right, tankless might have a chance. Until then, it'll always have Paris (and Tokyo and Rome and plenty of other cities across the globe).