Heat exchanger and water heating device including the same

A heat exchanger comprising:

• a casing into which heating gas is supplied;
• and
• a plurality of heat transfer tubes which are arranged in the casing and are configured as meandering tubes in which a plurality of straight tube portions arranged to be separated from each other are integrally connected to each other through a plurality of curved tube portions, and the straight tube portions connected to the same curved tube portions are located at a same level height,
• wherein the plurality of heat transfer tubes are set in a posture in which the plurality of straight tube portions are arranged in a direction intersecting a heating gas flow direction, are stacked in a plurality of stages in the heating gas flow direction, and are classified as first and second heat transfer tubes respectively located on an upstream side and a downstream side in the heating gas flow direction, and
• wherein the second heat transfer tubes are formed so that an outer diameter and an arrangement pitch of the plurality of straight tube portions are smaller than those of the first heat transfer tubes,
• pitches between both end portions of each of the first and second heat transfer tubes are the same, and
• a number of the straight tube portions and the curved tube portions of the second heat transfer tubes is larger than a number of the straight tube portions and the curved tube portions of the first heat transfer tubes.