The Velocity pumps are water cooled. They add ~ the same heat as a similar wattage submersible would. If you have a setup that runs hot already, its probably not the pump for you. Stick with an air cooled external. If the system doesn't run hot, they are great pumps. As I posted earlier, I am using one because of the "free" heat it adds. It saves electricity by reducing the amount of time my heaters have to kick in.