WHAT IS ALL-FUEL? A system designed and built to exhaust wood, coal, oil, or gas fired low heat residential appliances. These systems are commonly called a “Class A chimney” or a “Factory built chimney”. These are mainly used on free standing stoves, furnaces, and fireplaces. This product comes in double wall or triple wall construction. This type of system is listed to UL 103, UL 103HT, ULC S629, or ULC S604.