I keep a 125 reef. During the winter the temp in the room hovers around the lowish to mid 60's. I run 2 slightly underrated heaters on a controller with the probe in the overflow section of the sump and the heaters in the return section. The theory is that if one heater fails in the on position, the tank won't heat up too quickly, and if one fails in the off position, the tank won't cool down too quickly. In either case, my controller will alert me if my temp goes out of acceptable range. As of right now, my temp stays dead on 79 degrees.
As far as the warmer months go, the controller should shut down both heaters if temp goes above the set level and alert you if the temp rises too much. If temps in the room generally run in the mid 80's during the summer, you'll likely have to run fans over your display and/or sump to keep the temp down particularly when the lights are on.
Hope this helps.
