I too have a 220 gallon setup like yours, only mine is a reef tank, I do not use heaters, i use a chiller, my 180 gallon fresh with a Jardini Arowana in it uses a 300 watt stainless in the tank. If you have never used a sump and have ever let it go dry a heater is bad in sump. As long as your sump will "never" go below 2" of water you are fine. If it does, the heaters are not designed to shut off, they actually will overheat and can and have caused fires, I have witnessed this first hand, that is why my heaters all always in the tank.