Abstract: A wood and oil burning furnace having a combustion chamber in which logs are laid for burning, a baffle plate across a substantial portion of the top of the combustion chamber, a combustion gas outlet at the top of the chamber, a plurality of secondary air inlet tubes in the upper portion of the combustion chamber, a fan and secondary air preheating chamber in one wall of the combustion chamber and supplying preheated air to such tubes, and oil or gas burner, an auxiliary chamber connected through a port into the combustion chamber and directing the fluid fueled fire into the combustion chamber through the port which is located midway of the length of the sidewall of the combustion chamber.