This system is designed by HBC to combine the best technologies from the "old school" of coal combustion and the latest advanced combustion control technologies. The stationary underfeed stoker system provides a very low turn-down rate making it particularly suitable for heating applications in greenhouses, factories, schools and office buildings. This combination enables these systems to provide the most reliable operation utilizing a consistent single "grade" of low sulfur bituminous coal. Ash removal is available in manual and automatic configurations. The boiler vessel is a three-pass fire tube design incorporating a wet back turnaround that eliminates the need for rear door refractory.