Abstract: A direct gas-fired heating unit is provided which uses an axial-bladed fan for generating a main air flow through a burner unit. The burner unit has a dedicated combustion air blower supplying combustion air to the burner separate from a main air flow generated by the main fan. The burner unit includes a dedicated blower which draws a small volume of outside air as combustion air. Further, the burner unit may include bypass ports which allows for discharge of bypass air from the burner unit.