Weekend project : Window exhaust fan

I live in an old apartment where there is no fixed ventilation, not even a range hood. In the summer, when I want some fresh air, I simply open the windows. But in the middle of winter in Montreal, getting a blast of -20°C cold air each time you want some fresh doesn’t seem to be the best option… To fix the situation, this weekend I built a custom window exhaust fan.

By forcing the air out of a window, a gust of cold air cannot enter the apartment from the open window. Of course, all the indoor air that exits by the exhaust fan must be filled by exterior air. The advantage of the exhaust fan is that the air comes from all the small gaps in the building and is slowly warmed to room temperature. The main disadvantage of this solution is that it is very energy inefficient since cold air is constantly being warmed then thrown out.

I used 12V PC case fans because they are cheap and easily available. I settled on using two 140mm fans side by side since it is the maximum that could fit in my window.

The fans are installed on 1/4 inch hardboard that is cut and drilled using this template. The two large holes for the fans were cut using a jigsaw. The panel was painted white before assembly. For a better seal with the window, adhesive foam strips were added to the back.

On the electrical side, things are very simple. There is a barrel connector to plug in a 12V power supply and a power switch. The 12V power input and the fans are connected on a perforated board using polarized rectangular connectors. The cheap Chinese fans originally came with big 4 pins connector, which were cumbersome for this project. A custom cardboard box is put over the circuit and wire to protect them.

The electrical components used are detailed in the following table.

Component Digi-Key part number
Rectangular connector header  WM4300-ND
Rectangular connector housing WM2000-ND
Rectangular connector contact crimp WM1114-ND
Rocker switch EG4777-ND
Quick Connect crimp connector A107178CT-ND
Power barrel connector 839-1291-ND

The extractor was built to be easily installed and removed. It was initially only leaning against the window. This works perfectly in general, but if there is a strong gust of wind outside, a high pressure can build on the exterior side of the panel and push it inside. This happened a few times during the first days of used. Thankfully, the falls to the floor only chipped the corners as can be seen in the picture above. To fix the situation, a binder clip is used. It is attached to the window handle and forms a wedge that prevent the extractor from tipping over.


Cutting and drilling template