The term or abbreviation "W3G" provides information about three different properties of the exhaust system.
W: Condensate resistance class W
A condensate-resistant exhaust system can be operated in wet operation mode. It is important only that the inner tube is made of a high-quality material to compensate for the moisture.
3: Corrosion resistance class 3
The corrosion resistance class 3 allows the firing of the fireplace with liquid, gaseous and solid fuels.
G: Soot fire resistance
An exhaust system which, despite humid operation, is resistant to soot fire and also remains moisture-resistant after a possible fire.