I recently made a fan for my new grow box which is about 3'x6'x5', Optimum CFM from the calculator at: CFM Calc is around 100 cfm. With this in mind i made a trip down to home depot on concocted a fan and filter for under $35. Here it is:

2 - NuTone 50cfm fans $25.76 Fan Link
1 - Carbon filter = $9.97
Duct tape
extension cord
scrap plywood or plastic or cardboard(not fire safe)

Take the two fans with the exhaust outlets pointing up but them together to make a triangle.

Diagram1

Run the extension cord and Enclose the triangle with material and duct tape

Diagram2

Then cut a whole in the face for ducting.

Diagram3

To make the carbon filter work with the fans, cut it in half, use the plastic grate that came with it and role it into a 3" tube to fit your exuast tubes. and cap the end with duct tape and any other wholes. here is my final product.

Final Product

It works vary well for $35, a little loud but throw it in the attic and run ducting and you cant hear it.
ElementSpark Reviewed by ElementSpark on . GHETTO $35 100 CFM fan with Carbon Filter I recently made a fan for my new grow box which is about 3'x6'x5', Optimum CFM from the calculator at: CFM Calc is around 100 cfm. With this in mind i made a trip down to home depot on concocted a fan and filter for under $35. Here it is: 2 - NuTone 50cfm fans $25.76 Fan Link 1 - Carbon filter = $9.97 Duct tape extension cord scrap plywood or plastic or cardboard(not fire safe) Take the two fans with the exhaust outlets pointing up but them together to make a triangle. Rating: 5