i installed a navien gas i have very hard water i was always changing the heating elements on our electric water heater have experienced no problems with gas on demand.Yes in the winter our daughter does take incrediably long showers nowI want one in my home, but am afraid that since the water will not be softened/treated, that since Tulsa has a hard water, it would foul the heat exchanger! I have access to this http://www.quietside.com/Quietside/index.php?option=com_content&view=article&id=51&Itemid=96 at cost, as we have started to sell them, but am hesitant because of the water hardness. It does vent with PVC so it appears to be super efficient.