Installing two hot water heaters. I installed them in parallel with exactly the same length of pipe between them on the hot and cold sides. These tanks supply 14 showers and 10 sinks. We were running out of hot water before both tanks were spent of their hot water.(not quite balanced right…one still had hot water in it). Another plumber decided to change my installation and hooked the tanks up in series. I don’t think this is correct. One tank is doing all the work. I’d like to know if I should of installed balancing valves or circuit setters to make both tanks funtion correctly or is the series set-up correct? Thanks in advance.