An improved induction heating apparatus is provided for attaching membrane roofs. A top membrane layer is attached to attachment disks that hold sheets of thermal insulation to the top of roof substrates. The heating apparatus emits a magnetic field that raises the temperature of the disks and a heat-activated adhesive on top of the disks which, after cooling, becomes adhered to the bottom surface of the top membrane layer. The disks in turn are attached via fasteners to the substrate portion of the roof structure. The apparatus includes a set of bottom guides that allow a user to find the attachment disks mechanically, without actually seeing those disks beneath the top membrane layer. A triple-racetrack coil provides improved positioning tolerance in all directions, for coil placement during a heating event. An optional temperature sensor can “test” the heating effect on the top membrane layer, during/after a heating event.