Abstract: A water tube WT of a heat exchanger B includes a helical tube body 5 which includes a plurality of loops 50 arranged in the axial direction. At least one of the loops 50 includes an inclined tube portion which is inclined with respect to the axial direction and a non-inclined tube portion extending perpendicularly to the axial direction. The inclined tube portion is provided at each of opposite end regions s2a and s2b in a width direction crossing the axial direction, whereas the non-inclined tube portion is provided at an intermediate region S1 in the width direction. With this structure, the pitch p2 of the loops 50 is reduced. Therefore, by increasing the number of loops 50, high heat exchange efficiency is achieved without considerably increasing the size of the helical tube body 5.

Abstract: A water tube WT of a heat exchanger B includes a helical tube body 5 which includes a plurality of loops 50 arranged in the axial direction. At least one of the loops 50 includes an inclined tube portion which is inclined with respect to the axial direction and a non-inclined tube portion extending perpendicularly to the axial direction. The inclined tube portion is provided at each of opposite end regions s2a and s2b in a width direction crossing the axial direction, whereas the non-inclined tube portion is provided at an intermediate region S1 in the width direction. With this structure, the pitch p2 of the loops 50 is reduced. Therefore, by increasing the number of loops 50, high heat exchange efficiency is achieved without considerably increasing the size of the helical tube body 5.

Abstract: A secondary heat exchanger B for recovering latent heat from combustion gas includes water tubes 5 each of which is so inclined that a first end 50a is positioned lower than a second end 50b. Therefore, in draining water from each of the water tubes 5, water can be caused to flow smoothly into a water-inflow and hot-water-outflow header 6A connected to the first ends 50a. The secondary heat exchanger B includes a casing 7 which includes an upper wall 70a and a bottom wall 70b which are so inclined that the inner surfaces thereof extend generally in parallel with the water tubes 5, and the upper and the lower gaps 79a and 79b have constant widths s2 and s3. Therefore, the amount of heat recovery from the combustion gas passing through the gaps 79a and 79b can be increased.

Abstract: A secondary heat exchanger B for recovering latent heat from combustion gas includes water tubes 5 each of which is so inclined that a first end 50a is positioned lower than a second end 50b. Therefore, in draining water from each of the water tubes 5, water can be caused to flow smoothly into a water-inflow and hot-water-outflow header 6A connected to the first ends 50a. The secondary heat exchanger B includes a casing 7 which includes an upper wall 70a and a bottom wall 70b which are so inclined that the inner surfaces thereof extend generally in parallel with the water tubes 5, and the upper and the lower gaps 79a and 79b have constant widths s2 and s3. Therefore, the amount of heat recovery from the combustion gas passing through the gaps 79a and 79b can be increased.

Abstract: A water tube WT of a heat exchanger B includes a helical tube body 5 which includes a plurality of loops 50 arranged in the axial direction. At least one of the loops 50 includes an inclined tube portion which is inclined with respect to the axial direction and a non-inclined tube portion extending perpendicularly to the axial direction. The inclined tube portion is provided at each of opposite end regions s2a and s2b in a width direction crossing the axial direction, whereas the non-inclined tube portion is provided at an intermediate region S1 in the width direction. With this structure, the pitch p2 of the loops 50 is reduced. Therefore, by increasing the number of loops 50, high heat exchange efficiency is achieved without considerably increasing the size of the helical tube body 5.