I currently put a box fan in a window as an exhaust fan when I need to ventilate a room in my house. But when I turn the fan off, I need to remove the fan and close the window. I'd like to have a system with louvers that automatically close when the fan shuts off so I don't need to worry about hot air or bugs coming in. But I don't want a unit that requires any alterations to the window frame. Is there such a thing?

  • Last bathroom fan I saw actually had "motorized" louvers, using a simple electro-thermic actuator (simple and cheap, as opposed to motor + position sensor).
    – Dan
    Commented Jun 5, 2015 at 16:03
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2 Answers 2


Plenty of manufacturers make louvered fans that only require air flow (or the lack of) to operate the louvers. If you don't want to screw the flange to the window frame, you can attach a smaller one to a plywood insert, cut to fit snugly inside the frame.

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Whole-house fans are generally equipped with a motorized louver system.

Exhaust ducts (eg bathroom ventilation fans or clothes drier exhausts or kitchen exhausts) often have a seal of some sort which is simply blown out of the way while air is flowing, then closed by gravity.

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