immediately below gasket 126 is a damper blade 128 damper blade 128 is generally rectangular and operates to completely seal opening 122 when damper blade 128 is in abutting relationship with sealing gasket 126 damper blade 128 is fixedly secured to a lever arm 130 which is in turn hingedly connected to housing 22 at a pivot point 132 lever arm 130 is pivotally connected to a connecting link 134 which is in turn pivotally connected to a solenoid 136 solenoid 136 is secured to housing 22 via a holding bracket 138 and a spacer bracket 140 a cowling 142 is placed on housing 22 to cover solenoid 136 connecting link 134 and lever arm 130 cowling 142 defines an interior space 144 which allows damper blade 128 to pivot to an entirely open position as best seen in broken lines in fig1 further damper blade 128 may have secured thereto a layer of insulation 146 cowling 142 may be sized so as to allow blade 128 with insulation 146 thereon to pivot to a completely open position when damper blade 128 is pivoted to its completely open position damper blade 128 is completely away from the opening 122 formed in lip 120 in this manner damper blade 128 can be pivoted so as to not interfere with the overall cross sectional area of housing 22 in this embodiment fan 24 is located on the exterior.