I don't care if I catch flak for it but I am convinced that vent free is junk. I don't think they are healthy and can cause all sorts of other problems, such as excess humidity and resultant condensation and all related problems. If you want gas then go direct vent. There are tons of nice units out there, shop around. Read this two page article: http://www.jlconline.com/jlc/archive/energy/vent/index.html
If something goes wrong with a vent free you can die or become sick. This is not the case with units that vent to the outdoors, which common sense dictates.