A modulating burner apparatus includes a variable speed blower feeding a multi-chamber burner having first and second burner chambers. A manifold system communicates the blower with the burner, and a flow control valve member is located between the blower and the second chamber of the burner. The flow control valve is configured to provide fuel and air mixture from the blower to only the first burner chamber at lower blower speeds of the blower and to both the first and second burner chambers at higher blower speeds of the blower.