This was sent to me by one of my e-mail correspondents, Charleen. I asked if I could share it with others and she gladly gave me permission to reproduce it here.
Charleen and I exchanged multiple e-mails trying to resolve some issues with her proposed installation. The first is the hood design itself:
This is the final drawing we worked with. The exhaust comes out the back wall at the top and the fresh air is ducted in to the workspace also through the back and spread across the width by the slit. The slit will be two inches high (supported by bent metal supports) which is just about the same area as the 10″ duct she will be using to supply fresh air into the enclosure.
Here is a side view of the system:
The window being used is located in a window well, and as you can see, the fresh air supply end is located above the upper edge of the window well. This is always my suggestion — window wells can easily trap unwelcome fumes (as well as unwelcome visitors such as rodents and birds), so fresh air ducting should always be terminated at least 12″ above the window well upper edge.
The exhaust duct in this installation will bend to one side and run along the house at least 10 feet and terminate under a sealed deck area. The exhaust fan will be enclosed in a water tight enclosure as well.