I am looking into purchasing a zero clearance vent free fireplace. Does anyone have any comments on how much of a condensation problem this could cause with intermittant use. Best guess would be 2-3 hours of use in the evening. I currently use a vent free heater in the basement without any moisture problems. My concern is with using the two units at the same time will this cause moisture problems. Or also, a problem with carbon monoxide posioning?