Exactly...that's the only reason I went with the closed loop to the water heater. Peace of mind is a huge factor with planning a big reef tank. And aren't monster plug in heaters crazy expensive? For 1500 gallons of water, you'd need 4500 watts of heat right? I could be wrong, but I think it's 3 times water volume for heaters. So divide 4500 x 500 and that means you'd need nine in line 500 watt heaters.
Well there was a reason why I asked about cost of gas vs electricity, I'm sure I can easily look up those rates for Buffalo, NY but hey it's not my tank
Some areas have crazy low electrical rates (at least compared to what I pay), and some areas do not have natural gas availability and I've heard propane isn't cheap which is why I didn't suggest tying into a gas water heater (needs to be gas to have any chance of being useful, electrical water heater you might as well put heaters in your tank).
As to how many heaters are needed, it's a little more than just gallons. I forget what was told to me some 10+ years ago, but it was something like 1 watt per gallon per 5 degrees below ambient temperature. So if the room with the tanks is 60 degrees, that's 1500g x 1 x 4 (80-60=20 then divide by 5 = 4). So if you had all the inner workings of the tank inside an uninsulated garage, get ready to pay through the nose during the winter months, heck here in San Francisco I get hit fairly hard for ambient temps in the 50s.
Another option is to insulate a fish area behind it, and physically keep that warm with your furnance/boiler/etc, again unsure about gas prices, but around here stores tend to keep themselves warm rather than rely on electric heaters to keep their tanks warm. Now the downside to this approach is you'll more likely than not be fighting the humidity too, so some sort of heat exchanger that saves some the heat while evacuating the moisture is a must with a tank that size.
