A:Answer You need to move the warm air outside, so yes venting is necessary. The long answer is that there is a compressor generating heat inside the unit. It generates at least as much heat as you remove when you cool the air. The net effect would be no change in room temperature, maybe even an increase if not vented outdoors.
There are evaporative coolers that use water or ice for cooling and would not need to be vented. They are generally inexpensive because they do not require a compressor or refrigerant. I'm not very familiar with these style units but would speculate that you would have limited cooling ability from a portable unit. In addition the water or ice would have to be renewed periodically.
