Abstract: A thermally actuated diffuser for controlling room temperature without electrical apparatus. The thermally actuated diffuser includes a housing having a first duct opening and a second duct opening. The second duct opening is diametrically opposed to the first duct opening to produce a linear air path through the housing. The housing has a third exit opening for communicating with a room. A damper blade diverts air flow and is positioned in the interior of the housing. The housing contains a first device and a second device that are both responsive to ambient temperature. The first and second devices each have first and second ends. The first end and the second end are adapted to move away from each other when the device is warmed and to move toward each other when the device is cooled. The first device is positioned in the interior of the housing adjacent to the air path. The second device is positioned in the housing adjacent to the third exit opening.