We have had ventless for years. Like you, we have a flu and on the recommendation of the plumber who hooked up the fireplace, we leave it open slightly. The advantage of more heat is nice at the cost of looking slightly less realistic than vented logs. I have never encountered any issues with moisture. YMMV.
Previous: 1993 Prostar 205
Red 1998 Ski Nautique, PCM GT40, 310 hp, , Acme 4 blade, Perfect Pass SG/Zbox.
Be kind. Have fun.