Dear Coach: You honestly don't need the complexity of two water heaters. One properly sized gas tankless unit will supply all the hot water you need. If you must have high volumes of hot water in bursts, I can suggest a system for you, but most homes are served perfectly, with one simple unit. You will also see savings on your gas bill because you won't be storing large volumes of hot water 24hrs/day, just waiting to be used. If I can be of further assistance, please contact me at 1 800 851 9891. Sincerely, Brian Wood.