A heating system has a heating unit with a combustion chamber for burning wood pellets or other pelletized fuel. The heating unit is controlled by a process control module that automatically keeps all operating functions within predetermined limits for safe, efficient and easy operation. The unit also includes a combustion air distribution assembly with a stir shaft that rotates within the combustion chamber and introduces combustion air through orifices along the length of the shaft to enhance fuel combustion. A thermo cycle plumbing assembly serves as a safety feature by preventing overheating in the event of a power failure or pump failure. Also included in the unit is a removable insulated firebox burn chamber that provides a high temperature combustion atmosphere and a heat/particulate recovery module which provides maximum heating efficiency and reduces emissions, meeting EPA requirements and contributing to a cleaner environment.