We do need some more information to give a good accurate reply.
"Vent free" means quite a number of different things to different people, please describe the gas logs and the fireplace construction in more detail. For example, is the fireplace masonry construction with a chimney or a metal firebox surrounded by wood or masonry construction?
If you live within the City of Houston, the municipal ocdes are on the website. Most current information indicates the City has not amended the plumbing or fuel gas code as published by ICC, so typically an "unvented" heating appliance would not be allowed.
Our Texas members may know the situation better, how 'bout it guys.