Go with the Rinnai, you wont be sorry with a good installer.

I currently have a Takagi TK3 and have used on-demand in my past residence and my current vacation cottage.

In all I have used these heaters for almost 20 years with great success.

The cold water sandwich is typical in a cheaper unit such as the Bosch. I have never experienced one myself, perhaps due to thermostatic balancing shower valves.

Hi,
If you use 20 gallons per person per day, your water heating requires about 45000 BTU/day. With a 65% efficient conventional gas heater this would be about 0.72 therm of NG, with an 85% efficient tankless heater, it would be about 0.53 therm per day. The saving is about 0.2 therm per day -- at $2 per therm, this would be a bit less than 50 cents a day, or $180 per year saving (you can check what you pay per therm on your gas bill).
So, for the extra $750 you might save around $180 a year, and you would also reduce your CO2 emissions correspondingly. The savings go up as NG prices go up. You also get a water heater that will likely last more than twice as long.

I don't understand the comment above about venting. The tankless heaters use an extremely safe vent system, and in any case there is no connection between the vent system and the potential for explosions.

Gary

Dan, Please stop posting disturbing unrelated propane explosions at a factory/distribution plant and attempting to relate them to residential applications. Makes no sense.

Double wall vent pipe "special venting" is completely unrelated. Double wall galv/alum "b-vent" has been used for many years. Just because the higher efficient water heaters, furnaces, fireplaces, wall heaters, and so on require SS due to higher combustion efficiencies has NO correlation with safety, and definitely canÂt be tied to explosion risks.

BTW, the on-demand water heaters can be vented 30'+, just wouldnÂt make sense with the cost of venting materials and combustion clearances.

carolb....if you are in a southern clime, you may want to consider a heat recovery unit on your A/C-heat pump...Hot water for free is better than even paying a little.....

Gary