Abstract: A sleeve heater has a pair of end tubes centered on a common axis and having axially confronting and spaced inner ends, an electrically resistive helicoidal heating coil centered on the axis, and at least one tubular center tube coupled to the end tubes at the inner ends thereof and axially and angularly slidable on at least one of the end tubes so that the length of the heater can be adjusted. The coil has a pair of end sections of relatively shallow pitch in the end tubes and a center section of relatively steep pitch between the inner ends. Thus with this system the user can alter the length of the sleeve heater.