Abstract: An inspection apparatus for furnace flues and chimneys includes a reflecting plate biasly coupled, at its lower end to an interior wall of the flue. The reflecting plate is urged, by the bias coupling, to a non-use position adjacent the interior wall of the flue. The plate is moved to its reflecting or use position, within the interior of the flue, by the movement of a connecting rod operatively connected to the reflecting plate. In the reflecting plate use position, light entering the flue from the top is reflected to a sight glass in the flue wall. The absence of reflected light from the reflecting plate indicates an obstruction of the flue.Also disclosed is a modular inspection device for use with existing furnace flues.