What happens if you open the damper with a vent-free gas log setup?

I'm looking at the vent-free and vented gas log setup, and was wondering if you can operate the vent-free setup with the damper open. Main reason I'd be interested in doing so is if it's not too terribly cold, but we still want the fire going for "ambience", and we wanted to let some/most of the heat escape up the chimney instead of just circulating back into the room.