Acrylic or plate glass coverings are very bad for the leaded glass and wooden sash / casement, as this type of covering has a 'windshield' effect which magnifies the sun's heat. Sealed coverings trap heat and moisture causing accelerated oxidation of the lead came resulting in structural weakness. Sealed coverings can also rot the wooden sash / casement and sill plate by trapping heat and moisture.
The photos below show the Waddington Methodist Church in Waddington, NY and how we 'vented' their existing acrylic coverings using 2" soffit vents to allowing heat to travel upwards and out. The 2" vents have louvers to prevent water from entering and screen to stop insects.
