Take great care with this projec! A build up of paint fumes can be highly explosive
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I remember Scale Automodeler did an article on building a spray booth a few years back and they reconed it was best to get a fan designed for the job. The problem was the sparks from the motor of a regular electric fan could cause the fumes to explode...
Let me know how you get on, I've just moved house and now have my own modelling room, so I'm planning on building a booth when I have the time (and I'm not building cars!).