A computer-aided design (CAD) system may support detection of internal channel networks for 3D printing and may include a CAD model access engine and a channel network detection engine. The CAD model access engine may access a CAD model of a physical object to be constructed through 3D printing. The channel network detection engine may detect an internal channel network included in the CAD model of the physical object, including by identifying channel openings along a surface of the CAD model that satisfy an opening size threshold and recursively identifying internal faces of the CAD model that form the internal channel network, wherein the internal faces are faces of the CAD model that are internal to the surface of the CAD model. The channel network detection engine may also perform a channel verification on the identified internal channel network to support the 3D printing of the physical object.