I've seen pics of folks doing this in side. IIRC, they had a box fan blowing air into the room, and another box fan stuck in a window to exhaust air. And a CO detector.
Hell, I practically brew inside. I brew inside my garage, door down, all sealed up, in the winter. Of course, the garage door isn't an airtight seal, but it's not far off. I use two turkey fryers and have a 40000 BTU NG garage heater mounted to the wall, oftentimes all three running at full blast, (I've found all three running at full blast can rocket my garage up to 90*F in under an hour....and that's when it's -5* outside...). I just keep a CO detector on the workbench next to me, and no worries.