The HDG R is a log gasification boiler from HDG Bavaria in Germany. Logs go into the fuel chamber and the wood gases burn out in a hot combustion chamber directly below it. This method, called downward combustion, gives a clean and complete burn.

A variable speed flue gas fan holds the fuel chamber under negative pressure, which makes lighting up and cleaning quick and tidy. A flue gas temperature sensor sets the primary air and the boiler output, secondary air is preheated as it passes through the burner nozzle brick, and the air openings can be set for hardwood or softwood.

Integrated turbulators clean the heat exchanger and keep efficiency up. They are worked from the side with a lever that can be fitted on the left or right. A cleaning opening on top gives easy access to the heat exchanger, an insulated cover keeps heat loss low, and the flue gas outlet can be rotated to suit the chimney connection.