Systems, tools, and methods are presented that enable a plurality of turbulators to enhance heat transfer within a heat exchanger of a heating, ventilating, and air conditioning (HVAC) system. The plurality of turbulators each include a ribbon member having a variable pattern formed over a length. In one instance, the variable pattern of the ribbon member includes a plurality of bends defining intervals of alternating pitch. The intervals progressively increase in dimension as the ribbon member is traversed over the length. In another embodiment, the intervals contain apertures whose area increases as the length is traversed. Other systems, tools and methods are presented.