We wondered why some of the heating coils were so much smaller than the bottoms of our full-size pans. One factor is that a smaller coil is cheaper to manufacture, so the less expensive units tended to have coils about 6 inches in diameter, while the priciest and most powerful unit's coil was approximately 9 inches.
An induction cooktop also needs a fair amount of space around its coil: space for the electronics, for a cooling fan, and—as David Perreault, professor of electrical engineering at the Massachusetts Institute of Technology, told us—space that provides a path for the magnetic flux generated by the coil to return to, as well as room for airflow to cool the coil. The bigger the coil, the more space needed. The burner with the largest heating coil was almost twice as tall as the other models. That vertical space was mostly dedicated to its extensive fan system (one fan to cool the coil and another to cool the underside of the glass, a company representative told us). The large coil is likely why this burner toasted flour the most evenly and why it was the only model able to bring water to a boil faster than the stove.
While strange boiling patterns and unevenly toasted flour aren’t major issues, smaller heating coils also caused uneven cooking. Models with the smallest heating coils produced burgers with burnt patches on the parts of the patties that were toward the center of the pans and undercooked patches on the parts near the edges of the pans. Burners with larger heating coils were able to cook the burgers evenly, with no over- or underdone spots. If you invest in an induction burner that has a smaller heating coil, such as our Best Buy, we recommend using it with smaller cookware: skillets or saucepans that measure 10 inches in diameter or less.
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