Abstract:
The present invention provides a heat exchanger for bathing shower comprising an upper deck, a lower chassis and two hatches. On the bottom surface of the upper deck are disposed several parallel septa, whose integral propping strength is good enough to support maximal body weight of a bathing user. After having assembled, the circulation of internal water passages is configured into a continual zigzag duct to increase energy saving effect in consequence of improvement in heat exchanging efficiency of the water heater. With simple structure, it is easily fabricated by traditional extruding method without welding process and related welding technician. Thereby, selling price is reduced with marketing competitiveness because overall manufacturing cost is decreased so that the purchasing intention of the consumers is spurred. Thus, it is not only favorable to promote and penetrate marketing range and depth but also valuable to achieve energy saving and carbon reducing effect.

Description:
FIELD OF THE PRESENT INVENTION 
       [0001]    The present invention relates to a heat exchanger for bathing shower with features in good heat exchanging efficiency, simple structure and easy fabrication so that manufacturing cost is decreased and energy saving efficiency is increased. Thereby, the purchasing intention of the consumers is spurred and energy saving and carbon reducing effects is promoted. 
       BACKGROUND OF THE INVENTION 
       [0002]    For the purpose of reducing carbon product, many heat exchangers for bathing shower used in household have been introducing in the market. The design concept is that the incoming cold tap water running through in the heat exchanger is heated up by the bathed hot waste water, which is served as thermal source, so that the temperature of output tap water from heat exchanger becomes warmer than that of incoming tap water for being redirected into an inlet pipe for the water heater of bathing shower. Thereby, the temperature of the inlet water for the water heater of bathing shower is increased to result in saving energy source for heating water. Taking China Patent for title “Water heater of energy saving type” in Number of CN201016505 at New Model invention publicized on Feb. 6, 2008 as an example, as shown in  FIGS. 1 through 3 , the “Water heater of energy saving type” comprises a water heater  10 , which includes a water outlet pipe  12  and a shower sprayer  13 , and a metal heat absorbing slab  20 , which comprises a hollow chamber  21  with a top surface  24 , a water inlet pipe  23  and a water outlet pipe  22  such that said hollow chamber  21 , which allows cold tap water W 1  flows therein, has one end thereof with water outlet pipe  22  connected to a water intake  11  of the water heater  10  and the other end thereof with water inlet pipe  23  connected to a source of cold tap water W 1  (as shown in  FIGS. 1 and 2 ). Upon a shower user M standing on the metal heat absorbing slab  20  for starting shower, certain hot shower water W, which comes from the water heater  10  and flow through a water outlet pipe  12 , will spray out of the shower sprayer  13 . The hot shower water W will drop on the flat top surface  24  of the metal heat absorbing slab  20  after showering on the body of the shower user M, meanwhile certain cold tap water W 1  will flow into the hollow chamber  21  of the metal heat absorbing slab  20  via the water inlet pipe  23  and circulate among all hollow chamber  21  to absorb thermal energy of the dropped hot shower water W on the top surface  24  of the metal heat absorbing slab  20  so that the cold tap water W 1  becomes warm heat-exchanged water W 2 . The warm heat-exchanged water W 2  then flows out of the water outlet pipe  22  of the metal heat absorbing slab  20  to flow into the water heater  10  orderly via the water outlet pipe  22  and the water intake  11  thereof for serving as warm feeding water (as shown in  FIG. 2 ). Thereby, the energy saving effect for electricity of gas consumption of the water heater  10  is achieved. 
         [0003]    Please refer to  FIGS. 4 and 5  that show another exemplary embodiment for the water heater  10  of a metal heat absorbing slab  200 . The metal heat absorbing slab  200  comprises a spiral metal tube  201 , which is configured into planar serpent disk through multiple metal working process. The spiral metal tube  201  has multiple continual coils with a gap S for each pair of adjacent coils, one end thereof with water outlet pipe  22  connected to a water intake  11  of the water heater  10  and the other end thereof with water inlet pipe  23  connected to a source of cold tap water W 1 . By heat exchanging means of the spiral metal tube  201  between (hot shower water W) dropped on the top surface of the metal heat absorbing slab  200  and cold tap water W 1  will flow into the spiral metal tube  201  of the metal heat absorbing slab  200 , the cold tap water W 1  flowed in the spiral metal tube  201  becomes warm heat-exchanged water W 2 . The warm heat-exchanged water W 2  then flows out of the water outlet pipe  22  of the metal heat absorbing slab  200  to flow into the water heater  10  orderly via the water outlet pipe  22  and the water intake  11  thereof for serving as warm feeding water. Thereby, the energy saving effect for electricity of gas consumption of the water heater  10  is achieved. 
         [0004]    However, some drawbacks still exist in the China Patent for title “Water heater of energy saving type” in Number of CN201016505 at New Model invention as following: 
         [0005]    1. Please refer to  FIGS. 1 through 3  for metal heat absorbing slab  20 . In order to keep the hot shower water W drop on the top surface  24  of the metal heat absorbing slab  20 , the shower user M must stand on the top surface  24  of the metal heat absorbing slab  20 . Consequently, the metal top surface  24  with hollow chamber  21  beneath will be indented deformation owing to body weight strain of the shower user M for long term use (as hypothetical line shown in  FIG. 3 ). Because metal heat absorbing slab  20  is fabricated by metal welding process, water leakage is incurred from certain metal welding seams on the metal heat absorbing slab  20  being fractured due to indented deformation thereon so that not only the heat exchanging effect will be lost but also certain fractured metal welding seams may cause accidental hurt to the shower user M inadvertently. Moreover, because no circulation directing means is designed in the hollow chamber  21 , water turbulences will happen in the chamber  21  after cold tap water W 1  flows into therein via the water inlet pipe  23  (as indicting arrow heads shown in  FIG. 2 ) so that the energy saving effect will be considerably decreased in consequence of lowering heat exchanging efficiency. 
         [0006]    2. Please refer to  FIGS. 4 and 5  for metal heat absorbing slab  200 . Likewise, in order to keep the hot shower water W drop on the top surface of the metal heat absorbing slab  200 , the shower user M must stand on the top surface of the metal heat absorbing slab  200 . Because metal heat absorbing slab  200  is formed by spiral metal tube  201  having multiple continual coils with a gap S for each pair of adjacent coils, the round top surface thereof becomes slippery once hot shower water W drops thereon so that the shower user M stands thereon often suffered from injure inadvertently incurred by falling down due to such round slippery surface (as shown in  FIG. 4 ). That is a menace to the safety of the shower user M. Moreover, all the gaps S between each pair of adjacent coils in the spiral metal tube  201  cause no heat exchanging function as the hot shower water W passes therein without contacting to the spiral metal tube  201  (as shown in  FIG. 5 ) so that the energy saving effect will be considerably decreased in consequence of lowering heat exchanging efficiency. 
         [0007]    3. The key process for the manufacturing of metal heat absorbing slab  20  in  FIG. 1  and metal heat absorbing slab  200  in  FIG. 4  is metal welding process, which cause relative high labor cost in manufacturing expense as metal welding process is often worked by high-skilled technician with high salary to maintain high yield. Moreover, the multiple continual coils with a gap S for each pair of adjacent coils for fabricating the spiral metal tube  201  must processed by a tube-bending machine of high accuracy together with metal welding process for welding connection with water inlet pipe  23  and water outlet pipe  22  respectively so that overall manufacturing cost keep soaring high without possibility of lowering down. Thus, the ex-factory price and retail price for the product of metal heat absorbing slab  20  and  200  become particular high with difficulty for lowering down so that not only the purchasing intention of the consumer is retarded but also the product itself becomes unpopular. 
         [0008]    Therefore, how to contrive an improved product of heat exchanger for bathing shower with simplified structure and relative low manufacturing cost to satisfy with the purchasing ability and intention of customers seem very critical. 
       SUMMARY OF THE INVENTION 
       [0009]    The primary object of the present invention is to provide a heat exchanger for bathing shower with following features: (1) integral propping strength is good enough to support maximal body weight of a bathing user; (2) the circulation of internal water passages is configured into continual zigzag duct to considerably increase energy saving effect in consequence of improvement in heat exchanging efficiency of the bathing water heater; (3) simple structure and easy fabrication by traditional extruding method without involving welding process and related high-salary welding technician. Thereby, selling price can be substantially reduced with strong marketing competitiveness because overall manufacturing cost is decreased without sacrifice quality so that the purchasing intention of the consumers is spurred. Thus, the present invention is not only favorable to promote and penetrate marketing range and depth but also valuable to expedite in achieving the eco-friend effect of energy saving and carbon reducing requirement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is the first structural schematic view for the conventional heat exchanger of China Patent in No. CN201016505. 
           [0011]      FIG. 2  is a sectional view taken along line  2 - 2  as indicated in  FIG. 1 . 
           [0012]      FIG. 3  is an operational schematic view for the conventional heat exchanger of China Patent in No. CN201016505. 
           [0013]      FIG. 4  is the second structural schematic view for the conventional heat exchanger of China Patent in No. CN201016505. 
           [0014]      FIG. 5  is the third structural schematic view for the conventional heat exchanger of China Patent in No. CN201016505. 
           [0015]      FIG. 6  is an exploded perspective view of a heat exchanger for bathing shower according to a first preferred embodiment of the present invention. 
           [0016]      FIG. 7  is a perspective schematic view showing an upper deck under drilling bores process by a drilling tool for the above first preferred embodiment of the present invention. 
           [0017]      FIG. 8  is a perspective schematic view showing an upper deck for the above first preferred embodiment of the present invention. 
           [0018]      FIG. 9  is the first perspective schematic view showing assembling process for the above first preferred embodiment of the present invention. 
           [0019]      FIG. 10  is the second perspective schematic view showing assembling process for the above first preferred embodiment of the present invention. 
           [0020]      FIG. 11  is the third perspective schematic view showing assembling process for the above first preferred embodiment of the present invention. 
           [0021]      FIG. 12  is a sectional view taken along line  12 - 12  as indicated in  FIG. 11 . 
           [0022]      FIG. 13  is a sectional view taken along line  13 - 13  as indicated in  FIG. 11 . 
           [0023]      FIG. 14  is an installed schematic view showing practical usage for the above first preferred embodiment of the present invention. 
           [0024]      FIG. 15  is a sectional view taken along line  15 - 15  as indicated in  FIG. 14 . 
           [0025]      FIG. 16  is a illustrative schematic view showing extruding process for the above first preferred embodiment of the present invention. 
           [0026]      FIG. 17  is a perspective schematic view showing an upper deck under fraise process by milling cutter for the above first preferred embodiment of the present invention. 
           [0027]      FIG. 18  is a perspective schematic view showing an upper deck after deck fraise process by milling cutter for the above first preferred embodiment of the present invention. 
           [0028]      FIG. 19  is an exploded perspective view for the second preferred embodiment of the present invention. 
           [0029]      FIG. 20  is an assembly schematic view for the second preferred embodiment of the present invention. 
           [0030]      FIG. 21  is an exploded perspective view for the third preferred embodiment of the present invention. 
           [0031]      FIG. 22  is an assembly schematic view for the third preferred embodiment of the present invention. 
           [0032]      FIG. 23  is an exploded schematic view for the fourth preferred embodiment of the present invention. 
           [0033]      FIG. 24  is an assembly schematic view for the fourth preferred embodiment of the present invention. 
           [0034]      FIG. 25  is an assembly schematic view for the fifth preferred embodiment of the present invention. 
           [0035]      FIG. 26  is an operational schematic view for the fifth preferred embodiment of the present invention. 
           [0036]      FIG. 27  is an exploded perspective view for the sixth preferred embodiment of the present invention. 
           [0037]      FIG. 28  is an assembly perspective view for the sixth preferred embodiment of the present invention. 
           [0038]      FIG. 29  is a sectional view taken along line  29 - 29  as indicated in  FIG. 28 .  FIG. 30  is a sectional view taken along line  30 - 30  as indicated in  FIG. 28 . 
           [0039]      FIG. 31  is a sectional view taken along line  31 - 31  as indicated in  FIG. 28 . 
           [0040]      FIG. 32  is a perspective schematic view for the seventh preferred embodiment of the present invention. 
           [0041]      FIG. 33  is an exploded sectional view for the seventh preferred embodiment of the present invention. 
           [0042]      FIG. 34  is an assembly sectional view for the seventh preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    Referring to  FIGS. 6 through 13 , a heat exchanger for bathing shower according to a first preferred embodiment of the present invention comprises a stacked upper deck  30 , a founded lower chassis  40  and two hatches  50 . 
         [0044]    Referring to  FIGS. 6 through 13 , the upper deck  30  is a planiform cuboid extruded by metal material and encompassed by a top surface  31 , a bottom surface  32 , a front side  33 , a rear side  34 , a pair of parallel flanks  35 , includes a plurality of screw bores  36  created in the front side  33  and rear side  34  respectively, several parallel septa  37  downwardly disposed on the bottom surface  32  such that a water passage  303  is created between each pair of adjacent septa  37 , an upper docking latch bar  38  in male dovetail cross section being downwardly formed on the terminal of one septum  37 , a circulating bore  39  being created on each septum  37  in interlaced stagger manner, which means a circulating bore  39  in upper section of one septum  37  and another circulating bore  39  in lower section of the other septum  37  for each pair of adjacent septa  37 , so that all the adjacent water passages  303  can be mutually communicable as a continual zigzag circulating duct even being separated by a septum  37  between them, a water intake  301  is created in one flank  35  while a water outtake  302  is created in the other opposed flank  35  respectively; 
         [0045]    The lower chassis  40  is a planiform slab extruded by metal material and encompassed by a top surface  41 , a sole surface  42 , a front side  43 , a rear side  44 , a pair of parallel flanks  45  with same planar shape and area with corresponding upper deck  30 , includes a plurality of screw bores  47  created in the front side  43  and rear side  44  respectively, and a lower docking latch bar  46  in female dovetail cross section, which is upwardly formed on the top surface  41  in a suitable position corresponding to the upper docking latch bar  38  of the specific septum  37  on the upper deck  30  so that the male dovetailed upper docking latch bar  38  and the corresponding female dovetailed lower docking latch bar  46  can be securely engaged in mutual latch manner; and 
         [0046]    The each hatch  50  is a planiform slab with suitable planar shape and area to properly cover an interim integral assembly of the upper deck  30  and lower chassis  40  in flush manner, has a plurality of punched holes  51  disposed thereon in corresponding to the screw bores  36  on the upper deck  30  or screw bores  47  on the lower chassis  40  so that both of front and rear hatches  50  can hermetically seal both front sides  43  and  44  as well as both rear sides  34  and  44  of the interim integral assembly of the upper deck  30  and lower chassis  40  in plenum manner including all water passages  303  of continual zigzag circulating duct with septa  37  therein (as shown in  FIG. 12 ). 
         [0047]    Referring to  FIGS. 9 through 11 , the assembling process is described as below. 
         [0048]    Firstly, align and insert the male dovetailed upper docking latch bar  38  on the upper deck  30  into the female dovetailed lower docking latch bar  46  on the lower chassis  40  (as shown in  FIG. 9 ); 
         [0049]    Secondly, simultaneously apply forces on both of the rear side  34  on the upper deck  30  and the front side  43  on the lower chassis  40  in opposed inward manner to dock both of the upper deck  30  and lower chassis  40  up to flush manner so that a interim integral assembly of the upper deck  30  and lower chassis  40  is assembled (as shown in  FIG. 10 ); and 
         [0050]    Finally, cover both of front and rear hatches  50  on both front sides  43  and  44  as well as both rear sides  34  and  44  of the interim integral assembly of the upper deck  30  and lower chassis  40 , then drive (screws N) in the punched holes  51  on the upper deck  30  through the punched holes  51  on the lower chassis  40  to securely fix the interim integral assembly of the upper deck  30  and lower chassis  40  into a final plenum (as shown in  FIG. 11 ). 
         [0051]    For all foregoing assembling process, only few three simple steps are required without involving any welding process and related welding technician so that manufacturing cost is substantially reduced owing to low human labor and labor hour. 
         [0052]    Please refer to  FIGS. 14 and 15 . The installation and operation methods for a heat exchanger for bathing shower of the present invention are described as below. By means of proper pipe fittings, connect a water inlet pipe  23  of tap water to the water intake  301  on the upper deck  30  while connect a water outlet pipe  22  in water intake  11  of a water heater  10  to the water outtake  302  on the same upper deck  30  to finish the installation before operation (as shown in  FIG. 14 ). For shower, firstly, upon a shower user M starting shower, certain hot shower water W, which comes from the water heater  10  and flow through a water outlet pipe  12 , will spray out of the shower sprayer  13 ; secondly, the hot shower water W will drop on the flat top surface  31  of the upper deck  30  after shower on the body of the shower user M, meanwhile certain cold tap water W 1  will flow into the water passages  303  of the upper deck  30  orderly via the water inlet pipe  23  and the water intake  301  of the upper deck  30 , then circulate among all water passages  303  by means of every circulating bore  39  on each septum  37  (as indicated by arrowhead shown in  FIG. 15 ) to absorb thermal energy of the dropped hot shower water W on the top surface  31  of the upper deck  30  so that the cold tap water W 1  becomes warm heat-exchanged water W 2 ; and finally, the warm heat-exchanged water W 2  then flows out of the water outtake  302  on the upper deck  30 ; and then flows into the water heater  10  orderly via the water outlet pipe  22  and the water intake  11  thereof for serving as warm feeding water (as shown in  FIG. 14 ). Thereby, the energy saving effect for electricity of gas consumption of the water heater  10  is achieved. 
         [0053]    It is known from  FIGS. 14 and 15  that the plural septa  37  in each pair adjacent water passages  303  formed between the bottom surface  32  of the upper deck  30  and the upper surface  41  of the lower chassis  40  also serve as props (as indicated by enlarged view shown in  FIG. 14 ), which is strong enough to completely support normal body weight of a shower user M so that not only the service life span of the integral plenum of the upper deck  30  and lower chassis  40  can be extended due to no indented deformation being able to happen thereon, but also the shower user M suffered from injure inadvertently incurred by falling down can be avoided because the flat top surface  31  on the upper deck  30  offers stable platform for shower user M to stand thereon (as shown in  FIG. 14  and indicated by enlarged view associated). Moreover, the circulating bore  39 , which is created on each septum  37  to make every pair adjacent water passages  303  become water communicable mutually, serves as a circulation directing means in the heat exchanging slab  30  (as indicated by arrowhead shown in  FIG. 15 ) for directing the cold tap water W 1  to become a smoothly regular path-oriented stable flow in the water passages  303  between the upper deck  30  and lower chassis  40  so that the heat exchanging efficiency of the present invention is improved and the energy saving effect of the water heater  10  is substantially increased. 
         [0054]    All the foregoing upper deck  30  and lower chassis  40  of the present invention are produced by traditional extruding method. Referring to  FIG. 16 , take fabrication of the upper deck  30  as an example. Firstly, melt raw material of aluminum alloy by an extruder A, then extrude it out as a continual upper deck slab  300  via an extruding die B; secondly, cut the continual upper deck slab  300  into piece form of desired length by a cutting tool C, and finally, drill all circulating bores  39  by a drilling tool D (as indicated by hypothetical lines shown in  FIG. 7 ), and then a finished upper deck  30  is produced. The fabrication of the lower chassis  40  can be done in the same way as well. For all foregoing fabricating process, only few traditional techniques and related tools are required without involving any complicated process and related expensive machinery so that manufacturing cost is substantially reduced because fabricating process can be done in mass production of continuous production line with low human labor and labor hour. 
         [0055]    Please refer to  FIGS. 17 and 18 , which show an upper deck under fraise process by milling cutter for the first exemplary embodiment of the present invention. The foregoing drilling process in creating circulating bores  39  by a drilling tool D can be adapted by replacing a milling cutter G for the drilling tool to cut out equivalent circulating notches  391  in indented manner, which still function as circulating bores  39  (as shown in  FIG. 17 ). 
         [0056]    Comparing to conventional fabricating process, which involves welding process and related welding technician, the fabricating process of the present invention only with drilling tool D in creating circulating bores  39  or milling cutter G in creating circulating notches  391  eliminating welding process is apparently much simpler. Thereby, the marketing competitiveness of the present invention can be considerably enhanced in consequence of the manufacturing cost being substantially reduced from low human labor and labor hour. Thus, to promote energy saving campaign in recycling hot shower water W for the water heater  10 , the present invention can play an important role for immediate effectiveness. 
         [0057]    Referring to  FIGS. 19 and 20 , they show the second exemplary embodiment of the present invention. Wherein, the upper deck  30  is further modified to dispose a male dovetailed inward flank latch bar  351  on each flank  35  thereof while the lower chassis  40  is further modified to dispose a corresponding female dovetailed outward flank latch bar  451  on each suitable marginal position of upper surface  41  thereof (as shown in  FIG. 19 ). By means of additional engagement from the pair of male dovetailed inward flank latch bar  351  and the corresponding female dovetailed outward flank latch bar  451 , the interim integral assembly of the upper deck  30  and lower chassis  40  can be securely docked in much better manner (as shown in  FIG. 20 ). 
         [0058]    Referring to  FIGS. 21 and 22 , they show the third exemplary embodiment of the present invention. Wherein, the upper deck  30  is further modified to dispose a male dovetailed upper docking latch bar  38  on every septa  37  on the bottom surface  32  thereof while the lower chassis  40  is further modified to dispose a corresponding equivalent number of female dovetailed lower docking latch bars  46  on each suitable marginal position of upper surface  41  thereof such that each lower docking latch bars  46  is in corresponding to a matched upper docking latch bar  38  (as shown in  FIG. 21 ). By means of additional engagement from all male dovetailed upper docking latch bars  38  and the corresponding female dovetailed lower docking latch bars  46 , the interim integral assembly of the upper deck  30  and lower chassis  40  can be securely docked in much better manner (as shown in  FIG. 22 ). 
         [0059]    Referring to  FIGS. 23 and 24 , they show the fourth exemplary embodiment of the present invention. Wherein, the original male dovetailed upper docking latch bar  38  on the upper deck  30  is modified into a female dovetailed upper docking latch bar  38  while original female dovetailed lower docking latch bar  46  on the lower chassis  40  is modified into a corresponding male dovetailed lower docking latch bar  46  (as shown in  FIG. 23 ). By means of engagement from the new pair of female dovetailed upper docking latch bar  38  and the corresponding male dovetailed lower docking latch bar  46 , the interim integral assembly of the upper deck  30  and lower chassis  40  can be securely docked in same effect as that engagement from the original pair of male dovetailed upper docking latch bar  38  and the corresponding female dovetailed lower docking latch bar  46  (as indicated by enlarged view shown in  FIG. 24 ). 
         [0060]    Referring to  FIGS. 25 and 26 , they show the fifth exemplary embodiment of the present invention. Wherein, the top surface  31  on the upper deck  30  is modified into a cambered top surface  31  (as shown in  FIG. 25 ) to facilitate the sprinkled hot shower water W to easily drain out without and accumulation on the cambered top surface  31  of the upper deck  30  so that heat exchanging effect is not reduced due to cooling effect of the accumulated hot shower water W thereon (as shown in  FIG. 26 ). 
         [0061]    Referring to  FIGS. 27 through 31 , they show the sixth exemplary embodiment of the present invention. Wherein, each internal hatch face  501  of the front hatch and rear hatch  500  is modified to inwardly create an array of terminal linking passages  502  of zigzag end therein to replace the function of the circulating bores  39  or circulating notches  391  (as shown in  FIG. 27 ). The assembling process for this sixth exemplary embodiment is shown in  FIGS. 27 through 31 , which is almost the same as that shown in  FIGS. 9 through 11 . After having securely engaged the integral assembly of the upper deck  30  and lower chassis  40  as well as modified hatches  500  by screws N, a configuration of zigzag circulation from combination of water passages  303  and terminal linking passages  502  is finished (as shown in  FIG. 29 ). By means of the terminal linking passages  502 , the fabricating process of the circulating bores  39  or circulating notches  391  can be obliterated to reduce manufacturing cost. 
         [0062]    Referring to  FIGS. 32 through 34 , they show the seventh exemplary embodiment of the present invention. Wherein, the upper deck  30  is modified to split into a primary upper deck  30   a  and an annexed subordinate upper deck  30   b  while the lower chassis  40  is also split into a corresponding primary one and a subordinate one (as shown in  FIG. 32 ) such that an additional recessed linking elbow bar  352  is disposed on a flank  35   a  of the primary upper deck  30   a  while an additional corresponding projected linking elbow bar  353  is disposed on a flank  35   b  of the annexed subordinate upper deck  30   b.  Moreover, a plurality of screw bores  354  are formed in the recessed linking elbow bar  352  while a plurality of punched holes  355  are perforated in the projected linking elbow bar  353  (as shown in  FIG. 33 ). By driving a screw N through each punched hole  355  and screwing with each corresponding screw bore  354 , the primary upper deck  30   a  and annexed subordinate upper deck  30   b  can be mutually engaged securely so that the covering area of the present invention can be enhanced with more flexibility to meet some specific requirement of irregularly expanded floor layout of the bathing room (as shown in  FIGS. 32 and 34 ). Preferably but not necessarily, the primary upper deck  30   a  is identical to the upper deck  30  while the width of the annexed subordinate upper deck  30   b  is less than that of the upper deck  30 . 
         [0063]    The metal material used in the upper deck  30  of the present invention can be replaced by a non-metal synthetic material with good heat conductivity such as carbon fiber, which also has the same heat exchanging effect for hot shower water W in energy-saving function of the water heater  10  as that of the metal material. In conclusion all the disclosure heretofore, the simple structure with less fabricating process of the present can definitely reduce the manufacturing cost other than considerably energy-saving effect for the bathing water heater. Thus, it meets the basic criterion of patentability.