4 400 watt metal halides, 6 250 watt metal halides, 8 110 watt VHOs, large return pump, two large skimmer pumps, one 12,600 BTU split AC unit running 24/7, one 10,000 BTU window AC to keep my room icy cold at night, a 4 ton home AC unit that is a few years old (14 SEER), and a pool pump running. Our last bill was $577, but this next one will be a doozy with the last two weeks over 100 degrees each day.
I would reckon that your old AC unit is an energy hog and the summer heat is the reason it is running all the time. The calculator takes given values and works with them, simple math. What each electrical device actually uses in your aquarium could be seen with a killawatt meter. Welcome to the jungle
By the way, us Ameren folks are actually rewarded for using more electricity in the other 8 months, hence the discount over 750 kilowatt hours, gotta love that
