What Causes a Gasoline Heater to Smoke?
Natural gas and propane are smokeless fuels, therefore whenever your gas heater is smoking, then it is because something else is burning. More often than not, the culprit is debris or dust that has gathered over the burner after the heater was idle for an extended period.
First Seasonal Use
It is typical for a gas heater to smoke when you start it for the first time in the season, and the smoke generally dissipates quickly as debris is incinerated. If you would like to protect against this, blow off the burners with compressed air before beginning the heater. You can also eliminate debris by brushing it off, but that may require some disassembly to get the burners.
New Heaters
When you purchase a new heater and then start it for the first time, you can observe an alarming amount of smoke to get the first few minutes of operation. This is due to the fact that the manufacturer coated the burner parts with a thin coat of oil to protect them from rust. The smoke is unavoidable and normal, and it goes off fast.