There s basically 4 reasons a vent free gas fireplace will produce soot like you described.
Vent free gas heater problems.
If yours is a ventless heater that burns oxygen from the room try opening the window slightly to increase air flow.
They must be inspected cleaned annually by a professional gas technician.
If the oxygen drops to an unhealthy low the oxygen detector will shut off the fireplace.
Shut off the unit including the pilot.
Because a ventless fireplace does not have a fresh air intake vent the fire burns the oxygen in the room.
The unit hasn t been serviced annually since you purchased it.
Allow the unit to cool for at least 30 minutes.
Inspect burner pilot and primary air inlet holes on injector holder for dust and dirt.
A vent free heater can provide that extra needed humidity.
Direct vent heaters draw exhaust air outside and blockages in the air vents.
Vent fee gas logs are not maintenance free.
The log s are out of place and are impinging the flames.
Blow air through the ports slots and holes in the burner.