The official owners manual says not to:

http://www.coleman.com/coleman/images/pdf/5466A.pdf

However, I have used it through a few hurricane power outages in my kitchen which was big enough that perhaps doesn't fall under the definition of "enclosed area." I think big rooms will probably be OK. Definitely not in a camper van or a tent though.

I hate to give bad advice so I feel like I should point out that while I have done exactly what you're asking can be done- nobody ever accused me of being brilliant. Take it for what it's worth.