In many areas across the world the issue is more about dealing with how to keep saltwater tanks and equipment running cooler to match their natural habitat. We rarely, if ever do, think about the regions that have to deal with cold winters, or where the temperature outside starts to cause your saltwater temperature to get close to dropping below the optimal degrees. In order to prevent this. many use both a combination of a chiller and heater to make sure that if it gets too hot, that the chiller can kick in and cool the water down. Likewise, when the water gets too cold, the heater can turn on and make the water warmer again.
Do you personally use a heater for your aquariums? If so, what brand did you stick with and what temperature do you have it set at to turn on?