What type of draft system is commonly used in older pellet combustors?

The correct answer is natural draft systems, which are commonly found in older pellet combustors. Natural draft systems rely on the inherent buoyancy of hot gases rising, creating a draft that enables combustion air to flow into the appliance. This process does not require any mechanical components or fans, which makes these systems simpler and often less expensive to operate.

In older pellet combustors, the temperature differences between the exhaust gases and the outside air create a natural draft, drawing air in through the combustion chamber. This type of system is more common in older designs primarily because they were built before advances in technology allowed for more sophisticated draft management systems.

While mechanical draft systems and forced air systems involve the use of fans and blowers to actively draw air into the combustion process or expel exhaust gases, they are more commonly used in modern appliances that require precise control over airflow and combustion efficiency. Positive pressure draft systems also use fans, but they create a different operational dynamic, which is not characteristic of the older designs typically associated with natural draft systems. Thus, when considering the vintage characteristics of older pellet combustors, natural draft systems stand out as the appropriate choice.