Looking for some advice please.... We have a "sealed" gas fireplace, with outside vent (chimney-less). Whenever we use it, there is are fumes that make it intolerable... smells to me like plastic burning. It is not a gas leak. I've spoken with neighbors who have same units that do not experience this problem. Who should I call to get this evaluated and repaired? plummer? heat/air person? other? TIA!