Heating apparatus

A heating apparatus comprising:

• a burner,
• a combustion gas passage for guiding combustion gas generated in the burner,
• a primary heat exchanger for heating water by heat of the combustion gas and positioned in the combustion gas passage, and
• a secondary heat exchanger for heating water by heat of the combustion gas and positioned in the passage downstream of the primary heat exchanger,
• wherein the primary and secondary heat exchangers are connected so that water having passed through the secondary heat exchanger flows into the primary heat exchanger,
• wherein the secondary heat exchanger comprises a number of heat receiving tubes arranged in parallel,
• the heating apparatus having a plurality of the burners and a plurality of the combustion gas passages, so that the apparatus consists mainly of a plurality of heating systems each constituted by at least one of the burners and at least one of the passages,
• the heating apparatus further having a plurality of the primary heat exchangers accompanying the heating systems respectively,
• wherein the secondary heat exchanger has a plurality of the heat receiving tubes extending over at least two of the heating systems.

A heating apparatus comprising:

• a burner,
• a combustion gas passage for guiding combustion gas generated in the burner,
• a primary heat exchanger for heating water by heat of the combustion gas and positioned in the combustion gas passage, and
• a secondary heat exchanger for heating water by heat of the combustion gas and positioned in the passage downstream of the primary heat exchanger,
• wherein the primary and secondary heat exchangers are connected so that water having passed through the secondary heat exchanger flows into the primary heat exchanger,
• wherein the secondary heat exchanger comprises a number of heat receiving tubes arranged in parallel,
• wherein the secondary heat exchanger is constituted by a pair of headers between which the heat receiving tubes are arranged in parallel, the headers each comprising a tube plate with a surface to which the heat receiving tubes are fixed and a passage-forming member positioned at another surface of the tube plate so as to form a part of a water passage,
• the heat receiving tubes being arranged in such a manner that a plurality of the water passages each constituted by a plurality of the heat receiving tubes are communicated mutually by a plurality of the passage-forming members, so as to make up a unitary passage in which water flows in turning flow direction.