My CC had the 2 water heaters and it's my understanding that it was for faster recovery since one larger heater has the same element as the smaller (10 gal. vs 20 gal.) so recovery time for the 2 smaller heaters was twice as fast as the one larger one. One of mine sprung a leak and I replaced the two with one 10 gal. heater and haven't known the difference. I think that the two heaters was overkill.