Circulated air just means one with a fan inside. The other kind is still air, which is one without a fan. You can get good hatch results in both kinds of bator, but they do have different temperature requirements. Your one should be set at 99.5F, and you should be able to measure that temperature anywhere inside the bator, cause the effect of the fan swirling the air around means that the temps throughout the bator should be pretty much the same wherever you stick your thermometer. A still air bator is a bit different. Without a fan, the air inside the bator is very still, and you get thermal layering which is where hot air rises to the top, and the air at the bottom is cooler. With a still air bator, you want the temp to be 101.5F, measured at the same level as the tops of the eggs.