I've brewed in the garage for many years without even cracking the door, but our garage is not insulated and has vented soffits, so there is a lot of airflow. I've never felt weird or anything. The moisture is kind of a concern, but with the vented soffits I think it's a non-issue. Better safe than sorry, though. A bit of prevention goes a long way. Recently I bought a Grainfather, so I'm shifting to indoor electric brewing, and it is soooo sweet. Be safe out there, fellas.