Personally speaking, as a person who uses a rheostat/dimmer for a single leo in a single tank, I would not use one of these for a "rack". If you're going to control the temperature of multiple enclosures from a single unit you're probably going to need a thermostat. Otherwise you'll be risking some real inconsistencies in temperature from one cell to the next. It takes me constant attention to make sure my temps are right with a rheostat and if I had more to take care of I'd be using a thermostat.