why does a gas fireplace produce soot?

Answer 1

Soot is just the carbon residue from burning just about anything.

A gas fireplace should not produce much soot because it uses either natural gas or propane for fuel and both of these should burn cleanly.

Possibly the burner isn't getting enough fresh air or maybe the burner has the wrong size adapter installed, but this is unlikely.

If the fireplace is producing a lot of soot you should have a repair man look at it right away.

Answer 2

Quite possibly because its not LPG and is Coal Gas