Gas furnace and air conditioner having the same

A gas furnace comprising:

• a fuel valve;
• a manifold that provides a passage of fuel passing through the fuel valve;
• a plurality of burners configured to burn fuel provided from the manifold and spaced apart from each other in a first direction;
• a plurality of heat exchangers that provides a passage of combustion gas generated by the plurality of burners;
• and
• a blower configured to cause a flow of air passing around the heat exchanger, wherein the manifold comprises:
• a first tube having one end connected to the fuel valve and that forms a first passage;
• a second tube that extends in the first direction, forms a second passage, and faces at least one of the plurality of burners;
• a third tube that extends in the first direction, forms a third passage, and faces remaining burners of the plurality of burners;
• and
• a three-way valve connected to the first tube, the second tube, and the third tube, wherein the three-way valve guides fuel passing through the first passage to flow to the second passage and the third passage or to the third passage, wherein the plurality of burners comprises:
• a first burner group with burners that faces the second tube;
• and
• a second burners group with burners that faces the third tube, wherein the three-way valve is positioned between the second tube and the third tube, wherein the gas furnace further comprises:
• a flange that is connected to the plurality of burners between the plurality of burners and forms a flame propagation port;
• a burner box that accommodates the plurality of burners and the flange;
• an igniter mounted to the burner box and adjacent to an exit of a burner positioned farthest from the first burner group among the burners in the second burner group;
• a flame detector mounted to the burner box and adjacent an exit of a burner positioned farthest from the second burner group among the burners in the first burner group;
• and
• an auxiliary detector mounted to the burner box and adjacent an exit of a burner positioned closest to the first burner group among the burners in the second burner group.