Greenhouse Window

[Bambi.1]

I remember my father had a greenhouse gadget that automatically opened,depending on the temperature inside,unfortunately he's not around to ask anymore,but l was wondering what they are called,if anything ? and does anyone know where the best place is to get one please  ???

[Bambi.1]

[Barnowl]

I think their proper name is automatic vent openers.

[Bambi.1]

Thanks Barnowl  :-*