50 gallon is NOT the max according to Cal Energy commision--
"I should've been clearer about my response - I was speaking of new construction only. The information you've taken from the CF-1R-ALT is actually an error and it is in the process of being revised. This rule only applies when you are adding one or more new water heaters, not replacing a water heater.
A replacement water heater is subject only to the mandatory measures. You may reference Standards Section 152(b)1.G. The standards are found at http://www.energy.ca.gov/title24/2008standards/.