With a Ranco or DIY controller, this isn't an issue. However, with an Aquarium controller....and in my case that's a ReefKeeper....I purposely run and "expansion sock" just for my heaters. This eliminates any excessive draw on the power bar, which might not be able to handle it. So if you're running an Aquarium controller (one of those things with, typically an eight outlet power bar), use an expansion sock for your heaters.
My expansion socket is just above the the upper right corner of that white outlet plate, and has my two heaters plugged into it.
Paul just wondering why on a Ranco or a DIY its not a concern and on an apex or reef keeper it is? How much do those expansion socks run? I might need to pick you brain more when I get into heater controls with my controller (more on wiring/power than programming)