Ventfree are notorious for persistent odors. If this is a logset installed into an existing fireplace, it should have had a Level II inspection prior to installation. A qualified hearth pro should have installed it and ensured you meet the stated clearances to combustibles. A hearth pro should have sized it to your room based upon your climatic zone, construction, room size and makeup air requirements and the IRC.
Get it checked out by a Pro before you burn it. Have them conduct combustion analysis along with the gas leak check.