If your fireplace cannot be vented, it would probably not be a good idea to install ventless gas logs. They are dangerous and in many communities the building codes do not allow them, especially in sleeping rooms because of the risk of carbon monoxide poisoning. If venting to the outside is not an option, consider an electric logs installation. Not as nice as gas, but at least you do not risk life and limb. Consumer Reports website has an article explaining why ventless is a bad idea.