It is possible that the unit needs to be serviced. If the unit has not been serviced on a yearly basis, it is likely that a layer of carbon has built up on the logs and burner assembly, causing the odor you are detecting. Vent free room heaters pull room air for combustion and along with that air comes dust, lint, and other air impurities. Over a year of use, the impurities are burnt off and the byproduct can build up on the log set. Each time the byproduct is heated, the smell is released into the room. I recommend having your installer or licensed gas fitter out to inspect and clean the set.
on November 3, 2014