Patent Publication Number: US-2022227200-A1

Title: Heating Arrangement and Heat Distribution Unit for Such a Heating Arrangement

Description:
CLAIM TO PRIORITY 
     This non-provisional patent application claims priority to and benefit of, under 35 U.S.C. § 119(e), German Patent Application DE 102021200499.7, filed Jan. 20, 2021 and titled “Heating Arrangement and Heat Distribution Unit for Such a Heating Arrangement”, all of which is incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to a heating arrangement and to a heat distribution unit for such a heating arrangement. 
     2. Description of the Related Art 
     Various quite different solutions for heating arrangements are known in the state of the art. This holds in particular for heating arrangements in recreational vehicles, like campers or caravans. Although, in recreational vehicles heating arrangements are quite suitable to provide several components and/or areas or zones of a recreational vehicle with heat, commonly several distinct heating apparatuses are combined to end up with a universal heating arrangement. For example, one first heating apparatus is provided to supply a floor heating with hot heating liquid. In addition, a second heating apparatus is coupled to a water supply line of water for sanitary and/or cooking purposes to heat said water prior to use. Finally, a third heating apparatus configured to heat the air within the recreational vehicle is provided. All these heating apparatuses are provided independently to each other as separate apparatuses but from together a universal heating arrangement of the recreational vehicle. Such conglomerated configurations often suffer from problems in compatibility of its distinct components and require large space. Sometimes, such conglomerated configurations offer a lower overall efficiency. Moreover, such conglomerated configurations are often expensive and maintenance-intensive, as each component has to be bought and maintained separately as in many cases only single components are available but no overall solution. 
     Accordingly, there is much space for further developments of such heating arrangements. In particular, a long-term desire exists for an overall all-in-one solution for such a heating arrangement. 
     SUMMARY 
     Present embodiments provide a heating arrangement which overcomes at least some of the aforementioned drawbacks of prior art arrangements. 
     This heating arrangement and the corresponding heat distribution unit are defined by the appended independent claims. Modifications for the heating arrangement are to be found in the dependent claims. 
     According to a first aspect, a heating arrangement, in particular a heating arrangement for recreational vehicles like campers or caravans, comprises a heating apparatus and a heat distribution unit. The heating apparatus comprises a heating unit configured to generate hot air and a first heat exchanging unit and a second heat exchanging unit. The first heat exchanging unit and the second heat exchanging unit are coupled to the heating unit to receive the hot air from the heating unit independently of each other. The first heat exchanging unit is configured for heat exchange between the hot air and a heating liquid. The second heat exchanging unit is configured for heat exchange between the hot air and ventilation air. The heat distribution unit comprises a hot heating liquid input connection coupled to the first heat exchanging unit such that the heat distribution unit can receive hot heating liquid from the first heat exchanging unit therethrough. The heat distribution unit comprises further a hot heating liquid output connection configured to be coupled to a hot heating liquid input connection of an external heating device. The heat distribution unit comprises a third heat exchanging unit. The third heat exchanging unit is configured to be coupled to an external liquid supply line and is further configured for heat exchange between the received hot heating liquid from the first heat exchange unit and liquid guided through the external liquid supply line. 
     Such a heating arrangement is configured to heat ventilation air, a liquid guided through the external liquid supply line and to provide the external heating device with hot heating liquid at the same time. For this, only one single heating apparatus supplemented with an appropriate heat distribution unit is to be provided. Thus, the total number of separate apparatuses forming the heating arrangement is reduced considerably. Moreover, the maintenance of the heating arrangement is simplified. According to the invention only one single heating apparatus and the heat distribution unit is to be maintained, instead of a maintenance of various distinct apparatuses from various suppliers combined with each other to form the heating arrangement. Finally, the required space is reduced considerably. According to the invention, distinct components like the heating unit of the heating apparatus are used to provide heat for various purposes. Thus, thanks to the invention it is not necessary to be provide a single component for each separate purpose. 
     The heat distribution unit is configured such that the external liquid supply line can be a standard water supply line of a recreational vehicle provided to supply water for sanitary and/or cooking purposes. Such a configuration allows to heat water for sanitary and/or cooking purposes with the heating arrangement in a simple and direct manner. 
     The heat distribution unit is configured such that the external heating device can be a floor heating of a recreational vehicle. Such a configuration allows to heat the floor of the recreational vehicle directly with the heating liquid from the heating apparatus in a simple and direct manner. 
     The third heat exchanging unit comprises a cold liquid input connection. The cold liquid input connection is configured to be coupled to a cold liquid supply of the external liquid supply line. Further, the third heat exchanging unit comprises a hot liquid output connection configured to be coupled to a hot liquid output device via the external liquid supply line. With such a configuration, the heating arrangement, and in particular the third heat exchanging unit of the heating arrangement, can be coupled thermally to the external liquid supply line in a simple and straight-forward manner. 
     The third heat exchanging unit is a high efficiency liquid to liquid heat exchanger. Such a configuration allows to increase the overall efficiency of the heating arrangement. 
     The heat distribution unit comprises a hot heating liquid main flow path leading from the hot heating liquid input connection of the heat distribution unit directly to the hot heating liquid output connection of the heat distribution unit. In addition, the heat distribution unit comprises a hot heating liquid side flow path branching off from the hot heating liquid main flow path and leading to the third heat exchanging unit. Thus, the flow of hot heating liquid towards the third heat exchanging unit is branched off from the main flow path, resulting in a highly flexible and functional overall configuration. 
     The heat distribution unit comprises a valve unit configured to control the amount of hot heating liquid branched off from the hot heating liquid main flow path into the hot heating liquid side flow path towards the third heat exchanging unit. Such a configuration allows to control the amount of heat supplied to the third heat exchanging unit for heat exchange with the liquid guided through the external liquid supply line. 
     The heating arrangement comprises a heating liquid pump configured to force a flow of the heating liquid through the heating arrangement. Such a configuration allows better control of the operation of the heating arrangement and at the same time improves the overall efficiency of the heating arrangement. In particular, the heating liquid pump is provided as component of the heat distribution unit. Thus, it is not necessary to equip the heating apparatus with such a heating liquid pump such that the heating apparatus can also be used for other configurations than for the heating arrangement. This allows to reduce the producing costs for the heating apparatus as in particular the use thereof is not limited to the discussed heating arrangements. 
     The heating apparatus comprises a cool heating liquid input connection. The cool heating liquid input connection is configured to be connected directly to a cool heating liquid output connection of said external heating device. Alternatively, the heat distribution unit comprises a cool heating liquid input connection configured to be connected to a cool heating liquid output connection of said external heating device, and a cool heating liquid output connection configured to be coupled to said cool heating liquid input connection of the heating apparatus. Thus, the heating liquid circle can be closed either via the heat distribution unit or directly with the heating apparatus. Of course, the heating arrangement can be configured such that it can be set up in both configurations. Thus, a user can choose between configurations. 
     The second aspect of the present invention refers to the heat distribution unit for and/or of any one of the above described the heating arrangements. Such an appropriate heat distribution unit is required to form such heating arrangements according to the present invention. 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. All of the above outlined features are to be understood as exemplary only and many more features and objectives of the various embodiments may be gleaned from the disclosure herein. Therefore, no limiting interpretation of this summary is to be understood without further reading of the entire specification, claims and drawings, included herewith. A more extensive presentation of features, details, utilities, and advantages of the present invention is provided in the following written description of various embodiments of the invention, illustrated in the accompanying drawings, and defined in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the present embodiments will become more apparent from the following detailed description with reference to the accompanying drawings, in which: 
         FIG. 1  is a spatial view of an exemplary heating apparatus for a heating arrangement according to one exemplary embodiment; 
         FIG. 2  is a further spatial view of the heating apparatus of  FIG. 1 ; 
         FIG. 3  is a partially exploded illustration of the heating apparatus of  FIGS. 1 and 2 ; 
         FIG. 4A  is a spatial view of an exemplary coupling member for the heating apparatus of  FIGS. 1 to 3 ; 
         FIG. 4B  is an enlarged spatial view of the coupling member of  FIG. 4A ; 
         FIG. 5  is a spatial view of an exemplary burner for the heating apparatus of  FIGS. 1 to 3 ; 
         FIG. 6A  is an exploded illustration of an exemplary combustion air fan unit for the heating apparatus of  FIGS. 1 to 3 ; 
         FIG. 6B  is a spatial view of another exemplary combustion air fan unit for the heating apparatus of  FIGS. 1 to 3 ; 
         FIG. 7  is another partially exploded illustration of the heating apparatus of  FIGS. 1 to 3 ; 
         FIGS. 8A to 8C  are various spatial views of the heating apparatus of  FIGS. 1 to 3  with distinct elements omitted to show the inner structural configuration of said heating apparatus; 
         FIG. 9  is a spatial view of the heating apparatus illustrated in the above referenced FIGS. Supplemented with lines indicating various cross-sectional planes; 
         FIG. 10A  is a cross-sectional view of said heating apparatus along line A-A of  FIG. 9 ; 
         FIG. 10B  is a cross-sectional view of said heating apparatus along line B-B of  FIG. 9 ; 
         FIG. 10C  is a cross-sectional view of said heating apparatus along line C-C of  FIG. 9 ; 
         FIG. 11  is a schematic illustration of the overall structural configuration of the heating apparatus illustrated in the above referenced FIGS.; and 
         FIG. 12  is a schematic illustration of the structural configuration of a heating arrangement according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     At first, the concrete configuration of a heating apparatus  1  suitable to be used in a heating arrangement  100  ( FIG. 12 ) according to the present invention will be described in detail in view of  FIGS. 1 to 11 . Finally, the specific configuration of an exemplary embodiment of a heating arrangement  100  according to the present invention will be described with reference to  FIG. 12 . 
     As can be seen in  FIGS. 1 to 3 , an appropriate heating apparatus  1  comprises a heating unit  10 , a first heat exchanging unit  30  and a second heat exchanging unit  40 . The first heat exchanging unit  30  and the second heat exchanging unit  40  are both coupled to the heating unit  10  to receive hot air from the heating unit  10  independently of each other. In the illustrated embodiment, the first heat exchanging unit  30  and the second heat exchanging unit  40  are both coupled to the heating unit  10  in parallel with each other. 
     The heating unit  10  comprises a primary housing  12 , a secondary housing  14  and a coupling member  16  ( FIG. 4 ). The primary housing  12 , the secondary housing  14  and the coupling member  16  are coupled to each other and house further components of the heating unit  10 . The secondary housing  14  is coupled fixedly, for example via screw members, to the coupling member  16 . Alternatively, the secondary housing  14  can be formed integrally with the coupling member  16  as one-piece unitary member. The primary housing  12  of the heating unit  10  is coupled to the secondary housing  14  and to the coupling member  16  in a releasable manner. For example, the primary housing  12  of the heating unit  10  is coupled to the secondary housing  14  and to the coupling member  16  via clamping members or via a form fitting. This results in a configuration in which the primary housing  12  can be disengaged from the secondary housing  14  and the coupling member  16  in an easy and simple manner. This enables easy access to the interior components of the heating unit  10  for maintenance or the like. However, alternatively the primary housing  12  can be coupled to the secondary housing  14  and/or to the coupling member  16  via a configuration requiring the use of appropriate tools for disengagement. 
     The primary housing  12  is provided with an opening  12   a.  The opening  12   a  is covered with a removable lid (not illustrated). The lid allows access to the interior of the heating unit  10  in an easy but limited manner. The opening  12   a  is, for example, provided to enable a user to connect electrical connections for power, control and/or 230 V_AC electrical power to a circuit panel of a printed circuit board assembly (described later) of the heating unit  10 . In addition or alternatively, via the opening  12   a  other desired operations on the interior components of the heating unit  10  are possible without the need of removing the primary housing  12  or parts thereof. 
     At least the primary housing  12 , in particular also the secondary housing  14 , is provided with some ventilation slots  12   c  and  14   c.  The ventilation slots  12   c,    14   c  allow air from the exterior of the heating apparatus  1  to enter the interior of the heating unit  10 . In the illustrated configuration, in the assembled state of the heating unit  10  the ventilation slots  14   c  provided in the secondary housing  14  are configured to extend corresponding ventilation slots  12   c  provided within the primary housing  12 . In the present embodiment, on each of three different sides of the primary housing  12  a set of eight horizontal ventilation slots  12   c  is provided. However, also configurations with more or less than eight ventilation slots  12   c  per side, and/or other structural configurations for the ventilation slots  12   c  and  14   c,  like for example ventilation slots having circular or elliptical shapes or ventilation slots extending in vertical direction, are possible. 
     As illustrated in  FIGS. 4A and 4B  the coupling member  16  comprises basically a base portion  16   a,  a preheating portion  16   b,  a printed circuit board assembly coupling portion  16   c,  and two burner coupling portions  16   d  and  16   e  coupled to each other. Here, the coupling member  16  is a one-piece unitary member. The coupling member  16  can thus be formed in a single cast process. However, some or all of the various portions  16   a  to  16   e  of the coupling member  16  can be provided as independent parts coupled to each other in an appropriate manner. For example, the independent parts can be coupled to each other with screws or bolts, but of course other suitable means are possible as well. 
     The base portion  16   a  of the coupling member  16  comprises a bearing surface  16   a   1 . The bearing surface  16   a   1  has a plurality of through holes  16   a   2 . In the present configuration the bearing surface  16   a   1  has two through holes  16   a   2 . The number of through holes  16   a   2  can vary depending on the specific need. The through holes  16   a   2  allow appropriate bolts or screws to pass therethrough. Thus, the base portion  16   a  of the coupling member  16  can be fixed to a surface of the recreational vehicle like, for example, a wall, floor or ceiling area of the recreational vehicle or to any other suitable surface by the bolts or screws. The base portion  16   a  can be integrated into the secondary housing  14 . 
     The preheating portion  16   b  comprises a combustion air flow duct  16   b   1  and an exhaust gases flow duct  16   b   2 . The exhaust gases flow duct  16   b   2  is completely enveloped by the combustion air flow duct  16   b   1 . The two flow ducts  16   b   1  and  16   b   2  are at least partly separated from each other by only one heat transmitting separation wall  16   b   3 . Thus, heat is transferred between air within the two air flow ducts  16   b   1  and  16   b   2 . The combustion air flow duct  16   b   1  comprises an inlet opening  16   b   1 A and an outlet opening  16   b   1 B. The exhaust gases flow duct  16   b   2  comprises two inlet openings  16   b   2 A and  16   b   2 B as well an outlet opening  16   b   2 C coupled to each other, respectively. 
     The printed circuit board assembly coupling portion  16   c  is configured to attach a printed circuit board assembly (PCBA)  18  thereto in a releasable manner. In the illustrated configuration this is achieved via appropriate screws (not illustrated) engaging threaded bores  16   c   1  provided within the PCBA coupling portion  16   c.  Furthermore, the PCBA coupling portion  16   c  comprises a port that allows the sensing of the intake air pressure. In other embodiments, the structural element labeled with reference sign  16   c  is not provided to attach the PCBA  18  thereto. Instead, it is provided for the port for sensing the intake air pressure only. 
     Each of the two burner coupling portions  16   d  and  16   e  is provided as circular frame member having an interior opening and several engaging recesses. A single burner  20  and  22  can be inserted into each of the burner coupling portions  16   b  and  16   a  to be coupled to the corresponding heat exchanging unit  30  or  40 . Each burner  20  and/or  22  can be locked in this position via appropriate engaging members like screws or bolts (not illustrated). 
     The heating unit  10  is enclosed by the primary housing  12 . In the inner of the heating unit  10  the secondary housing  14  and the coupling member  16 , the PCBA  18 , two burners  20  ( FIG. 10A ) and  22  ( FIG. 10C ), a fuel gas or liquid piping  24  being coupled to the two burners  20  and  22  and having an inlet port configured to be coupled to a storage for fuel gas or liquid (not illustrated), a combustion air fan unit  26  and a ventilation air driving unit  28  are provided. In the scope of the present invention, the term “burner” refers to fuel manifolds, as illustrated. However, also other configurations for burners are possible. 
     The two burners  20  and  22  are inserted into the burner coupling portions  16   d  and  16   e  of the coupling member  16 . The two burners  20  and  22  protrude from the inner of the heating unit  10  with their flame generating side.  FIG. 5  illustrates an example for the structural configuration of a dual nozzle fuel manifold of the burners  20  and  22 , here in particular an exemplary embodiment of the second burner  22 . The first burner  20  can have the same or at least a quite similar configuration. The second burner  22  comprises a combustion air flow duct  22   a,  several (here in particular two) nozzles  22   b   1  and  22   b   2 , an ignition arrangement  22   c  and a controlling arrangement  22   d.    
     The combustion air flow duct  22   a  is configured to lead a flow of combustion air from a combustion air fan unit  26  coupled to an inlet opening  22   a   1  of the combustion air flow duct  22   a  (here the lower end thereof) to a combustion area  22   e  of the burner  22 . 
     The two nozzles  22   b   1  and  22   b   2  are provided with passive flow disturbance devices (not illustrated). The two nozzles  22   b   1  and  22   b   2  receive gas or liquid via a corresponding fuel gas or liquid piping  24  coupled thereto. The two nozzles  22   b   1  and  22   b   2  are thus configured to supply fuel gas or liquid to the combustion area  22   e  of the burner  22 . The two nozzles  22   b   1  and  22   b   2  consist of a first nozzle  22   b   1  and a second nozzle  22   b   2 . The second nozzle  22   b   2  is differing from the first nozzle  22   b   1  in a cross section of its supplying opening. Accordingly, the first nozzle  22   b   1  and the second nozzle  22   b   2  have different throughput rates. 
     The ignition arrangement  22   c  is configured to ignite the mixture of combustion air from the combustion air flow duct  22   a  with the fuel gas or liquid from the two nozzles  22   b.  In the illustrated embodiment, the ignition arrangement  22   c  is provided as electric arc or spark generating arrangement having two elongated electrodes. Here, the elongated electrodes serve also as flame detector and feedback unit, which will be referred to later. 
     The controlling arrangement  22   d  is configured to be coupled to the PCBA  18 . The controlling arrangement  22   d  is coupled to the ignition arrangement  22   c  and two fuel gas or liquid valves (not illustrated, but further referred to below). The PCBA  18  is configured to supply electrical power to the ignition arrangement  22   c  to operate the ignition arrangement  22   c  appropriately, for example, by generating an electric arc or spark for ignition within the combustion area. Each of the fuel gas or liquid valves is coupled to one of the two nozzles  22   b   1  and  22   b   2 . By the fuel gas or liquid valves, the fuel supply for each of the two nozzles  22   b   1  and  22   b   2  can be controlled independently of each other. Both fuel gas or liquid valves are monostable valves having an opened operation state and a closed state. Such monostable valves are well known in the art, which is why a detailed description thereof is omitted here for the sake of brevity. 
     With such a configuration, in principle, four states for the fuel supply at the combustion area  22   e  and, thus, four different heat outputs of the second burner  22  can be selected by the controlling arrangement: 
     In a first operation state, both valves are closed such that no fuel gas or liquid is provided to the combustion area  22   e.  Accordingly, there is no combustion process in the combustion area  22   e  and the heat output is zero. 
     In a second operation state, the fuel gas or liquid valve coupled to the first nozzle  22   b   1  is opened while the other fuel gas or liquid valve coupled to the second nozzle  22   b   2  is closed. Accordingly, fuel gas or liquid is provided to the combustion area  22   e  as defined by the throughput rate of the first nozzle  22   b   1 . This results in a first heat output. 
     In a third operation state, the fuel gas or liquid valve coupled to the first nozzle  22   b   1  is closed while the fuel gas or liquid valve coupled to the second nozzle  22   b   2  is opened. Accordingly, fuel gas or liquid is provided to the combustion area  22   e  as defined by the throughput rate of the second nozzle  22   b   2 . This results in a second heat output differing from the first heat output. 
     In a fourth operation state, both fuel gas or liquid valves are opened such that fuel gas or liquid is provided to the combustion area  22   e  with a third fuel supply rate defined by the combined throughput rate of the first nozzle  22   b   1  and of the second nozzle  22   b   2 . This results in a third heat output, wherein the third heat output substantially corresponds to the sum of the first heat output and the second heat output. 
     In the illustrated embodiment, the first burner  20  ( FIG. 10A ) in principle has the same structure as the second burner  22 . But in the present configuration the first burner  20  comprises just one single nozzle  20   b.  Moreover, only one fuel gas or liquid valve is provided. In the illustrated embodiment, it is not necessary to provide both burners  20  and  22  with the possibility to switch between four distinct operation states. Thus, providing the first burner  20  with only one nozzle  20   b  can save costs. Nevertheless, the first burner  20  can have the same configuration as the second burner  22 , if desired. 
     As illustrated in  FIG. 6A , the combustion air fan unit  26  comprises a first housing elements  26   a  and a second housing element  26   b,  one single combustion air fan  26   c,  and a combustion air fan driving unit  26   d  (seen in  FIG. 3 ) for the combustion air fan  26   c.    
     The first housing element  26   a  comprises a combustion air inlet opening  26   a   1  and two combustion air outlet openings  26   a   2  and  26   a   3 . The combustion air inlet opening  26   a   1  is coupled via a common O-ring (not illustrated) to the outlet opening  16   b   1 B of the combustion air flow duct  16   b   1 . The first outlet opening  26   a   2  of the first housing element  26   a  is coupled via a common O-ring (not illustrated) to the inlet opening of the combustion air flow duct of the first burner  20 . The second outlet opening  26   a   3  of the housing element  26   a  is coupled via a common O-ring (not illustrated) to the inlet opening  22   a   1  of the combustion air flow duct  22   a  of the second burner  22 . 
     The second housing element  26   b  is coupled to the first housing element  26   a  with several coupling members, like for example bolts or other suitable coupling means (not illustrated). The first housing element  26   a  and the second housing element  26   b  are configured to form a combustion air flow path. The combustion air flow path leads form the combustion air inlet opening  26   a   1  to a combustion air fan chamber  26   e.  Further, the combustion air flow path leads from the combustion air fan chamber  26   e  via two separate flow path sections to each of the two combustion air outlet openings  26   a   2  and  26   a   3 . The two sections of the combustion air flow path leading from the combustion air fan camber  26   e  to the combustion air outlet openings  26   a   2  and  26   a   3  can be provided with combustion air valves. Thus, each of the corresponding sections of the combustion air flow path can be closed by the respective combustion air valve. Thus, it is possible to control the supply of combustion air to the two burners  20  and  22 , for example, to enable an emergency shut down of the corresponding burner  20  or  22  and/or to increase the amount of combustion air provided to the other burner  22  or  20  coupled to the section of the combustion air flow path which is still open. 
     In the present embodiment, the one single combustion air fan  26   c  is provided with one single fan wheel. In particular, the single fan wheel is implemented as an impeller. Such a configuration allows to save space. The combustion air fan  26   c  is positioned within the combustion air fan chamber  26   e  which is formed by the two housing elements  26   a  and  26   b.  The combustion air fan  26   c  is positioned in a plane perpendicular with respect to the central axis of the combustion air inlet opening  26   a   1 . In the assembled state of the heating apparatus, the combustion air fan  26   c  is configured to generate a flow of combustion air from the combustion air inlet opening  26   a   1  towards both of the combustion air outlet openings  26   a   2  and  26   a   3  and, thus, to the two burners  20  and  22 . As such fans are commonly known, a detailed description thereof is omitted for the sake of brevity. 
     The combustion air fan driving unit  26   d  is provided on an outer surface of the second housing element  26   b.  A driving rod (not illustrated) extends through a driving rod through hole  26   b   1  provided within the second housing element  26   b.  The combustion air fan driving unit  26   d  is coupled via the driving rod (not illustrated) to the combustion air fan  26   c.  The combustion air fan driving unit  28  is configured to drive the combustion air fan  26   c  for generating the above described flow of combustion air. 
     In  FIG. 6B , another example for a combustion air fan unit  26  is illustrated. This combustion air fan unit  26  in this configuration has basically the same structural configuration as the one illustrated in  FIG. 6A , but comprises two separate combustion air fans  26   c.  Each of the two separate combustion air fans  26   c  is coupled to only one of the two combustion air outlet openings  26   a   2  and  26   a   3  (seen along the combustion air flow path). In other words, each distinct combustion air flow path for one of the burners  20  or  22  has its own combustion air fan  26   c.  Thus, it is possible to set the amount of combustion air provided to each of the two burners  20  and  22  more freely. 
     Referring to  FIG. 3 , the ventilation air driving unit  28  is configured to generate, in particular with a ventilation air fan provided in the ventilation air driving unit  28 , a flow of ventilation air from an inlet opening  28   a  of the ventilation air driving unit  28  towards an outlet opening  28   b  of the ventilation air driving unit  28 . As such ventilation air driving units are well-known from the state of the art the detailed description thereof is omitted for the sake of brevity. 
     The ventilation air driving unit  28  is coupled, for example with bolts or screws (not illustrated) or by other suitable means, to the secondary housing  14 . However, the ventilation air driving unit  28  can also be coupled to one of the other components of the heating apparatus  1 . For example, the ventilation air driving unit  28  can be coupled to the coupling member  16 . The inlet openings  28   a  of the ventilation air driving unit  28  are positioned in the vicinity of the ventilation slots  12   c  and  14   c  of the housings  12  and  14 . As can be seen in  FIG. 8C , a ventilation air outlet section  14   b  is provided within the second heat exchanging unit opening of the secondary housing  14 . The outlet opening  28   b  of the ventilation air driving unit  28  is positioned on the ventilation air outlet section  14   b.  Thus, the ventilation air driving unit  28  is configured to generate a ventilation air flow from the environment of the heating apparatus  1  through the ventilation slots  12   c  and  14   c  to the ventilation air outlet section  14   b.    
     As indicated above, the PCBA  18  is attached with the PCBA coupling portion  16   c  to the coupling member  16 . The PCBA comprises a control signal receiving unit, a processing unit coupled to the signal receiving unit and several control signal wires coupling the processing unit with the controlling arrangement (not shown) of the first burner  20  and the controlling arrangement  22   d  of the second burner  22 , the combustion air fan driving unit  26   d,  a controlling arrangement of the ventilation air driving unit  28  and a controlling arrangement for a bypass gas valve, which can be provided further. 
     The control signal receiving unit is configured to receive control signals via wired or wireless communication from a control signal input unit coupled to the control signal receiving unit. The control signal receiving unit is further configured to forward control signals to the processing units. For example, the control signal input unit can be a specific remote-control device or a common smart phone with an appropriate app sending control signals to the control signal receiving unit. This can be achieved by Bluetooth or by other suitable wireless communication. Alternatively, the control signal input unit can be provided as a control panel coupled to the control signal receiving unit via a cable. It is to be noted that control signals do not have to contain only direct control instructions. Control signals can also comprise, for example, various sensor signals. Sensor signals may, for example, come from temperature sensors provided in the heating apparatus or in the recreational vehicle, etc. Moreover, the control input signal unit can be provided as one single device. It can, however, also comprise or consist of several independent devices like serval sensors and/ or input devices transmitting control signals to the control signal receiving unit. 
     The processing unit is configured to receive and to process the control signals received from the control signal receiving unit and to generate appropriate instruction signals for the various components coupled to the processing unit. In particular, the processing unit comprises a memory. The memory can be one of a volatile or non-volatile memory. The memory can contain programs or the like allowing the processing unit to generate appropriate instruction signals from the received control signals. The generated instruction signals do not necessarily have to contain just digital signals, which then have to be processed by the respective components receiving such signals. The generated instruction signals can also include analogue signals for directly operating the respective components. For this purpose, the PCBA  18  further can contain a separate electrical power supply, like for example a battery. Alternatively or in addition thereto, the PCBA  18  can be configured to be coupled to an external energy source, for example like the power grid of the recreational vehicle, etc. 
     In the illustrated embodiment, the PCBA  18  is configured to control and/or operate the controlling arrangements of the two burners  20  and  22 , the combustion air fan driving unit  26   d,  the ventilation air driving unit  28  and a bypass gas valve, which can be further provided. Further components controlled and/or operated by the PCBA  18  will be discussed later. Within the scope of the present invention also other configurations for the PCBA  18  are possible. In particular, the PCBA  18  can be configured to use information about various temperatures, for example of an air temperature within the recreational vehicle or of the environment of the recreational vehicle, of a liquid temperature, for example of a fuel liquid of the heating apparatus  1  or a liquid to be heated with the heating apparatus  1 , etc., various pressure values and/or a flame ionization values of the burners  20  and  22  to control the various components of the heating apparatus  1  in an appropriate manner. 
     As indicated above, the heating apparatus  1  further comprises a first heat exchanging unit  30  and a second heat exchanging unit  40 . Both heat exchanging unit  30 ,  40  are coupled to the heating unit  10 . The first heat exchanging unit  30  and the second heat exchanging unit  40  will be described in the following referring to  FIGS. 7 to 8B . 
     The first heat exchanging unit  30  is configured to allow heat exchange between exhaust gases from the first burner  20  and a heating liquid to be heated. The first heat exchanging unit  30  comprises a liquid tank  32 , an exhaust gases piping  34 , a cold heating liquid piping  36  and a hot heating liquid piping  38 . Both of the cold heating liquid piping  36  and the hot heating liquid piping  38  are provided with connections by which they can be coupled to a heating liquid circuit (not illustrated). In the present configuration the heating liquid is a special liquid for heat transfer. However, in general also water can be used as heating liquid. 
     The liquid tank  32  comprises a tubular main body  32   a.  The tubular main body  32   a  is enclosed on a bottom side thereof by a bottom plate  32   a   1  and opened on a top side of the main body  32   a.  The top side of the main body  32   a  is sealed with a lid member  32   b . The lid member  32   b  has a central exhaust gases inlet opening  32   b   1 , an exhaust gases outlet opening  32   b   2 , a cold heating liquid inlet opening  32   b   3 , a hot heating liquid outlet opening  32   b   4 , two further equipment insertion openings  32   b   5  and  32   b   6  and a specific mounting structure. The mounting structure is configured to mount the lid member  32   b  and thus the liquid tank  32  to the heating unit  10 . Alternatively, the further equipment insertion openings  32   b   5  and/or  32   b   6  can be moved to the bottom plate  32   a   1 . 
     The exhaust gases piping  34  is provided to one end thereof with a combustion chamber section  34   a.  The combustion chamber section  34   a  is coupled to the lid member  32   b  of the liquid tank  32  in such a manner that, in the assembled state of the heating apparatus  1 , the combustion air flow duct of the first burner  20  is coupled to the combustion chamber section  34   a  of the exhaust gases piping  34  in a sealed manner. For this, a common O-ring can be provided between the first burner  20  and the exhaust gases piping  34 . Moreover, in the assembled state of the heating apparatus  1 , the combustion area of the first burner  20  is located within the combustion chamber section  34   a  of the exhaust gases piping  34  such that the combustion reaction of the first burner  20  can take place in the combustion chamber section  34   a  of the exhaust gases piping  34 . 
     The exhaust gases piping  34  further has a tubular exhaust gases leading section  34   b.  The tubular exhaust gases leading section  34   b  is coupled at one of its ends to the combustion chamber section  34   a  in a sealed manner. At its other end the tubular exhaust gases leading section  34   b  is coupled to the exhaust gases outlet opening  32   b   2  of the lid member  32   b.  In particular, the exhaust gases piping  34  is a one-piece unitary member having the combustion chamber section  324   a  and the exhaust gases leading section  34   b . However, also other configurations are possible. As is illustrated in the figures, the exhaust gases leading section  34   b  is provided in several loops within the main body  32   a  of the liquid tank  32 . This is to increase the contact surface between the exhaust gases piping  34  and a heating liquid provided within the liquid tank  32 . By doing so a heat transfer from the exhaust gases within the exhaust gases piping  34  to the heating liquid within the liquid tank  32  is increased. The exhaust gases outlet opening  32   b   2  of the lid member  32  is configured such that, in the assembled state of the heating apparats  1 , it is positioned on the first inlet opening  16   b   2 A of the exhaust gases flow duct  16   b   2 . Thus, the exhaust gases can flow from the exhaust gases piping  34  into the exhaust gases flow duct  16   b   2  of the coupling member  16 . The contact between the exhaust gases piping  34  and the exhaust gases flow duct  16   b   2  is sealed with an O-ring, for example in form of a silicon O-ring. The O-ring is highly heat resistant to seal the connection between the exhaust gases piping  34  and the exhaust gases flow duct  16   b   2  reliably. 
     The cold heating liquid piping  36  goes through the cold heating liquid inlet opening  32   b   3  of the lid member  32   b  into the liquid tank  32 . Thus, the heating liquid to be heated can be supplied to the inner of the liquid tank  32 . The hot heating liquid piping  38  goes through the hot heating liquid outlet opening  32   b   4  of the lid member  32   b  out of the liquid tank  32 . Thus, the hot heating liquid can be discharged from the inner of the liquid tank  32 . In the assembled state, and the finally set configuration of the heating apparatus  1 , the hot heating liquid outlet opening  32   b   4  and the hot heating liquid piping  36  have to be positioned at an upper position as compared to the cold heating liquid inlet opening  32   b   3  and the cold heating liquid piping  36  to achieve an expedient overall configuration. 
     In the illustrated embodiment, two electrically driven heating members  39  are inserted through the two equipment insertion openings  32   b  and  32   b   6  into the liquid tank  32 . The heating members  39  are coupled to the PCBA  18  to be controlled and/or operated by the PCBA  18 . The heating members  39  provide a further possibility to heat up the heating liquid within the liquid tank  32  either instead of or together with exhaust gases from the first burner  20 . Thus, an increased heating rate is achieved. Moreover, if desired, it is possible to heat the heating liquid within the liquid tank  32  by electrical power only. Other equipment components like temperature sensors or the like can be inserted through one of the equipment insertions openings  32   b   5  and  32   b   6  and/or at least one of the equipment insertion openings  32   b   5  and  32   b   6  can be closed by a removable lid member or may be sealed permanently. 
     The second heat exchanging unit  40  is configured to enable heat exchange between exhaust gases from the second burner  22  and ventilation air. For this, the second heat exchanging unit  40  comprises a ventilation air enclosure  42  and an exhaust gases piping  44 . 
     The ventilation air enclosure  42  comprises a tubular body section  42   a  and a lid section  42   b.  The tubular body section  42   a  is sealed at one side thereof with an end plate  42   a   1 . The end plate  42   a   1  is provided with a ventilation air inlet opening  42   a   1 A and an exhaust gases inlet opening  42   a   1 B. The end plate  42   a   1  is configured such that it can be coupled to the secondary housing  14  and/or the coupling member  16  in such a manner that, in the assembled state of the heating apparatus  1 , the ventilation air inlet opening  42   a   1 A of the ventilation air enclosure  42  is positioned on the ventilation air outlet opening  14   b  of the secondary housing  14 . Thus, the combustion area  22   e  of the second burner  22  protrudes through the exhaust gases inlet opening  42   a   1 B into the ventilation air enclosure  42 . Furthermore, the end plate  42   a   1  further comprises an exhaust gases outlet opening  42   a   1 C. The exhaust gases outlet opening  42   a   1 C is configured to be coupled via a silicone O-ring (not illustrated) to the second inlet opening  16   b   2 B of the exhaust gases flow duct  16   b   2  of the coupling member  16 . Said O-ring is highly heat resistant. 
     The lid section  42   b  is coupled at the other side of the body portion  42   a  to confine the inner space of the ventilation air enclosure  42 . The lid section  42   b  is provided as separate element. The lid section  42   b  comprises four ventilation air outlet openings  42   b   1  to  42   b   4  arranged in pairs on two opposing side surfaces of the lid section  42   b.  Of course, also other configurations for the ventilation air outlet openings  42   b   1  to  42   b   4 , like configurations with less or even more ventilation outlet openings and/or configurations having further elements like pipes or safety meshes, can be realized. 
     The exhaust gases piping  44  is provided to one end thereof with a combustion chamber section  44   a.  The combustion chamber section  44   a  is coupled to the end plate  42   a   1  of the ventilation air enclosure  42  in such a manner that, in the assembled state of the heating apparatus  1 , the combustion air flow duct  22   a  of the second burner  22  is coupled to the combustion chamber section  44   a  of the exhaust gases piping  44  in a sealed manner. For this, a common O-ring can be provided between the second burner  22  and the exhaust gases piping  44 . Moreover, in the assembled state of the heating apparatus  1 , the combustion area  22   e  of the second burner  22  is located within the combustion chamber section  44   a  of the exhaust gases piping  44 . Thus, the combustion reaction of the second burner  22  can take place in the combustion chamber section  44   a  of the exhaust gases piping  44 . 
     The exhaust gases piping  44  further has a tubular exhaust gases leading section  44   b.  One end of the tubular exhaust gases leading section  44   b  is coupled to the combustion chamber section  44   a  in a sealed manner. The other end of the tubular exhaust gases leading section  44   b  is coupled to the exhaust gases outlet opening  42   a   1 C of the ventilation air enclosure  42 . In particular, the exhaust gases piping  44  is a one-piece unitary member having the combustion chamber section  44   a  and the exhaust gases leading section  44   b.  However, also other configurations are possible. As is illustrated in  FIGS. 8A and 8B , the exhaust gases leading section  44   b  is provided in several loops within the body portion  42   a  of the ventilation air enclosure  42 . By providing the several loops the contact area between the exhaust gases piping  44  and a ventilation air within the ventilation air enclosure  42  is increased. This enables an increase of the heat transfer from the exhaust gases within the exhaust gases piping  44  to the ventilation air. The exhaust gases outlet opening  42   a   1 C of the main body  42   a  is configured such that, in the assembled state of the heating apparatus  1 , it is positioned on the second inlet opening  16   b   2 B of the exhaust gases flow duct  16   b   2 . Thus, exhaust gases can flow from the exhaust gases piping  44  into the exhaust gases flow duct  16   b   2  of the coupling member  16 . The contact between the exhaust gases piping  44  and the exhaust gases flow duct  16   b   2  is sealed with a heat resistant silicon O-ring. Thus, this connection is sealed in a reliable manner. 
     As for example can be seen in  FIG. 7 , the heating apparatus  1  further comprises a heat exchanging units housing shell  50  and a supplementary mounting member  52 . 
     The heat exchanging units housing shell  50  is a tubular member configured to be pushed onto the two heat exchanging units  30  and  40  and to be fixed to the heating unit  10 . The heat exchanging units housing shell  50  comprises a first heat exchanging unit section  50   a  and a second heat exchanging unit section  50   b  corresponding a respective one of the two heat exchanging units  30  and  40  in cross sectional shape as seen along their longitudinal axes. With the heat exchanging housing shell  50 , the overall configuration of the heating apparatus  1  gains structural stability and protection against external influences. 
     The supplementary mounting member  52  serves as lid member for the heat exchanging units housing shell  50 . The supplementary mounting member  52  is coupled to the heat exchanging units housing shell  50  on the side opposing the side to which the heating unit  10  is coupled. The supplementary mounting member  52  is coupled to the heat exchanging units housing shell  50  in an appropriate manner like, for example, via form-fitting or separate coupling means. The supplementary mounting member  52  comprises a first heat exchanging unit section  52   a,  a second heat exchanging unit section  52   b  and at least one mounting section  52   c  being coupled to each other. 
     The first heat exchanging unit section  52   a  of the supplementary mounting member  52  is configured to seal the first heat exchanging unit section  50   a  of the heat exchanging units housing shell  50 . 
     The second heat exchanging unit section  52   b  of the supplementary mounting member  52  consists of a frame defining a central opening. The central opening of the lid section  42   b  of the second heat exchanging unit  40  can be coupled to the body portion  42   a  of the second heat exchanging unit  40  in the longitudinal direction thereof. 
     In particular, the heating unit  10 , the first heat exchanging unit  30  and the second heat exchanging unit  40  are provided as independent self-contained components coupled to each other in a releasable manner to form the heating apparatus  1 . The heat exchanging units housing shell  50  is configured to enclose the two heat exchanging units  30  and  40  at least partly. Thus, the two heat exchanging units  30  and  40  cannot be separated from each other without removing the heat exchanging units housing shell  50 . The heat exchanging units housing shell  50  is configured to be coupled to the heating unit  10  in a releasable manner. The heat exchanging units housing shell  50  is configured to couple the heating unit  10  and the two heat exchanging units  30  and  40  to each other in such a manner that for removal of the heat exchanging units housing shell  50  and, thus, for disassembling of the heating apparatus  1 , the heat exchanging units housing shell  50  has to be decoupled from the heating unit  10  first. 
     As illustrated in  FIG. 7 , the supplementary mounting member  52  comprises two mounting sections  52   c.  One mounting section  52   c  is coupled to the first heat exchanging unit section  52   a  and the other mounting section  52   c  is coupled to the second heat exchanging unit section  52   b  of the supplementary mounting member  52 . Each of the mounting sections  52   c  is provided with a bearing surface having at least one through hole. At least one through hole  52   c   2  allows appropriate bolts or screws to pass therethrough. Thus, the supplementary mounting member  52  can be fixed to a desired and suitable surface of a recreational vehicle like, for example, to a wall, floor or ceiling of the recreational vehicle. 
     It is to be noted that the above described configuration is a preferred but merely exemplary embodiment of a heating apparatus  1  for a heating arrangement  100  according to the present invention. In particular, many of the above described structural features can be replaced by others or adapted if desired or necessary. Such modifications lie in the abilities and freedom of a skilled artisan without leaving the scope of the present invention. 
     To facilitate the understanding of the specific configuration of this exemplary embodiment (in particular with regard to the various flow paths)  FIGS. 10A to 10C  illustrate several cross sections of the heating apparatus  1  according to the present invention, while in  FIG. 9  the various cross-sectional planes are depicted. 
     In the following and in particular referring to  FIG. 11 , a method for heating fluids with the above described heating apparatus  1  according to the present invention is described. 
     The combustion air fan unit  26  is operated to suck combustion air from an external environment of the heating apparatus  1 . The combustion air is forced through the combustion air flow duct  16   b   1  of the preheating portion  16   b  of the coupling member  16  towards each of the two provided burners  20  and  22 , thus, generating an overpressure within the respective combustion areas. 
     Each of the two burners  20  and  22  is further supplied with fuel gas or liquid from a fuel gas storage or liquid storage coupled to the two burners  20  and  22 . Due to the fact that the second burner  22  is provided with two nozzles  22   b   1  and  22   b   2  to supply the fuel gas or liquid to the combustion area  22   e,  the rate with which fuel gas or liquid is supplied to the combustion area  22   e  can be switched between four various operation states by operating the respective valves, as described above in detail. Accordingly, it is not necessary to provide an expensive and error-prone burner with a complex structure to achieve various operation sates. The combustion air and the fuel gas or liquid are mixed with each other within the combustion areas. The mixtures obtained in the combustion areas are ignited by the respective ignition arrangements  20   c  and  22   c  to burn within the respective combustion areas. 
     Hot exhaust gases from the first burner  20  are guided through the exhaust gases piping  34  of the first heat exchanging unit  30  and transfer some of their heat to a heating liquid provided within the liquid tank  32  of the first heat exchanging unit  30 . Permanently, fresh cold heating liquid from a heating liquid circuit is supplied to the liquid tank through the cold heating liquid inlet opening  32   b   3 , while hot or at least heated heating liquid is discharged through the hot heating liquid opening  32   b   4  back into the heating liquid circuit. Thus, cold heating liquid is supplied to the heating apparatus  1  and hot/heated heating liquid is discharged from the heating apparatus  1   
     Hot exhaust gases from the second burner  22  are guided through the exhaust gases piping  44  of the second heat exchanging unit  40  and transfer some of their heat to the ventilation air. The ventilation air is forced by the ventilation air driving unit  26   b  to move from an indoor room of the recreational vehicle, respectively a space in which the air is to be heated, through the body portion  42   a  of the second heat exchanging unit  40  back to the indoor room. Thus, cold ventilation air from the indoor room or interior of the recreational vehicle is sucked into the heating apparatus  1  and heated ventilation air is discharged into the indoor room or interior from the heating apparatus  1 . 
     The exhaust gases leaving both of the heat exchanging units  30  and  40 , while the exhaust gases do still have high temperatures, are guided into the exhaust gases flow duct  16   b   2  of the preheating portion  16   b  and, thus, preheat the combustion air which is sucked through the combustion air flow duct  16   b   1 . This preheating results in a very efficient heating operation. Afterwards, the exhaust gases are discharged into the external environment. 
     Although, in the above described process, both of the ventilation air and the heating liquid are heated simultaneously, the heating apparatus  1  can be used as well for heating only one of the two fluids. As a skilled artisan will be able to consider various possibilities to operate the above described heating apparatus  1  resulting from its specific structural configuration, no detailed listing of all possible modes of operation is given here for the sake of brevity. 
     In the following, some exemplary modifications are described that improve the characteristics and/or functionality of the heating apparatus  1  according to the present invention. 
     According to a first modification, the heating apparatus  1  can be provided with a secondary air supply arrangement. By this secondary air supply arrangement, a supply of secondary air from the external environment to at least one of the burners can be realized. In such a configuration, the combustion air depicts the primary air. While the primary air is supplied to start a combustion reaction with the fuel gas or liquid, the secondary air is provided to complete the reaction. This results in an improved flame stability and emission characteristics. A burner with such a functionality is also called flat surface burner. A flat surface burner can be further provided with a wall, the wall having a plurality of apertures and being arranged to further separate the flow of primary air or combustion air from the flow of secondary air. In such a configuration, the dimension of the apertures is optimized as a function of the rate of secondary air, which in particular also depends on the provided fans. 
     Although, referring to the above embodiment a configuration with two burners is described, also implementations having more than two burners can be provided if desired. Preferably, even if more than two burners are provided, all of the burners can be supplied with combustion air by the one single combustion air fan, to transfer the therewith obtained simple and reliable setting to such a configuration. 
     Although within the scope of the above embodiment a configuration with only two nozzles  22   b   1  and  22   b   2  in the second burner  22  is described, the second burner  22  (and also the first burner  20 ) can be provided with more than two nozzles in order to implement more than four distinct operation states. 
     Although within the scope of the above embodiment a configuration in which both nozzles  22   b   1  and  22   b   2  of the second burner  22  have different structures (cross sections of their supply openings) are described, the nozzles  22   b   1  and  22   b   2  can have the same structure as well. Effectively, only three various operation states are, thus, realized. 
     According to one embodiment of a monostable valve, as used herein, includes a valve body having an inlet for connection to a fuel supply and an outlet for connection to the respective nozzle. A valve seat is positioned between the inlet and the outlet of the gas body. A valve member is linearly movable between a closed position or state and an open position or state. In the closed position or state the valve member is seated on the valve seat. In the open position or state the valve member is spaced from the valve seat. Usually, a spring acting on the valve member keeps the valve member in the closed position. A solenoid (electro-magnet) is fixed to the valve body and, when energized, acts on the valve member to move it to or keep it in the open position, i.e. when a gas injection is required. Conversely, when the solenoid is not energized the spring moves the valve member to or keeps the valve member in the closed position, i.e. when a gas injection is not required. Thus, the closure device moves linearly with respect to the electro-magnet, which is axially fixed. The solenoid is controlled and driven directly by the PCBA. No movable elements are provided for actuating the gas valve. The solenoid may be excited with two different current values: a constant first value and a constant second value, lower than the first one. Thus, when the gas valve is actuated for opening, the solenoid is firstly excited with the first value until a predetermined time, for example 100 ms, has passed, then it is excited with the second value. The transition from the first value to the second value is controlled and actuated by the PCBA depending on the time only, i.e. independently on the position of the valve itself. However, since the valve could not open instantaneously, for example in less than 100 ms, it is likely that the valve reaches the open position when the coil is excited with the second (lower) value. Then the valve is hold in the opening position as long as the coil is kept excited with the second value. 
     The liquid tank may be further coupled to a frost valve. The frost valve comprises a pressure valve and is configured to perform at least the following basic functions: manual drain, frost draining (automatic) and pressure relief. However, also other configurations are possible. 
     The heating apparatus  1  further comprises an external container. The components of the heating apparatus  1  are arranged in the external container. The external container shields the various components of the heating apparatus against harmful external influences like, for example, sun radiation, water or dirt. Further, the external container is made of molded plastic, as such a material is highly resistive to external influences and forces. 
     According to a further modification, the heating apparatus further includes a supplementary electric heater. The electric heater provides a heating coil to achieve a supplementary heating of the ventilation air. The electric heater can be positioned inside the external container, next to the second heat exchanger and is driven and controlled by the PCBA. Thus, it is possible to increase the heating power of the heating apparatus  1 . 
     The heating apparatus  1  may be provided with a master valve for cutting the supply with fuel gas or liquid centrally. 
     Now, the structural configuration and function of a heating arrangement  100  according to an exemplary embodiment of the present invention will be described with reference to  FIG. 12  in a situation, in which it is coupled to the relevant exterior components. 
     The heating arrangement  100  is formed of the above described heating apparatus  1  and a heat distribution unit  60 . However, next to the present embodiment also other heating apparatuses  1  and/or further components can be provided in the heating arrangement  100 , if desired. 
     As already set forth above, the heating apparatus  1  comprises a heating unit  10 , a first heat exchanging unit  30  and a second heat exchanging unit  40 . The heating unit  10  is configured to generate hot air. In the above example, the hot air corresponds to the hot exhaust gases or at least is part thereof. The two heat exchanging units are coupled to the heating unit  10  to receive hot air/exhaust gasses therefrom more or less independently of each other. For example, the two heat exchanging units are coupled to the heating unit  10  in parallel to each other. 
     The first heat exchanging unit  30  is configured to transfer heat from the hot air/hot exhaust gasses from the heating unit  10  to heating liquid within a heating liquid circle. The heating liquid circle guides the hot heating liquid form the first heat exchanging unit  30  to the heat distribution unit  60 . The heat distribution unit  60  comprises a hot heating liquid main flow path leading from a hot heating liquid input connection of the heat distribution unit  60  directly to a hot heating liquid output connection of the heat distribution unit  60 . Furthermore, the heat distribution unit  60  comprises a hot heating liquid side flow path branching off from the hot heating liquid main flow path and leading to a third heat exchanging unit  70 . 
     The third heat exchanging unit  70  comprises a cold liquid input connection. The cold liquid input connection is configured to be coupled to a cold liquid supply. The third heat exchanging unit  70  further comprises a hot liquid output connection. The hot liquid output connection is configured to be coupled to a hot liquid output device  80 . In other words, the third heat exchanging unit  70  can be coupled to an external liquid supply line leading from the cold liquid supply to the hot liquid output device  80 . 
     The third heat exchanging unit  70  is a high efficiency liquid to liquid heat exchanger. The third heat exchanging unit  70  is configured to transfer heat from the heating liquid within the heating liquid side flow path to the liquid within the liquid supply line. Thus, the cold liquid input into the third heat exchanging unit  70  is transformed into hot liquid supplied to the hot liquid output device  80 . The external liquid supply line can be a standard water supply line of a recreational vehicle provided to supply water for sanitary and/or cooking purposes and the hot liquid output device  80  can be a common faucet. 
     The heating liquid circle leads the still hot heating liquid from the heat distribution unit  60  towards an external heating device  90 . The external heating device  90  is configured to transfer heat from the still hot heating liquid to other components and or areas. For example, the external heating device can be a floor heating of a recreational vehicle. 
     Finally, the more or less cold heating liquid is guided back into the first heat exchanging unit  30  to be heated again. For this, the cold heating liquid can be guided through a cold heating liquid flow path within the heat distribution unit  60  or directly towards the first heat exchanging unit  30 . 
     To be able to control the amount of hot heating liquid branched off from the hot heating liquid main flow path into the hot heating liquid side flow path towards the third heat exchanging unit  70 , the heat distribution unit  60  comprises a corresponding valve unit. Furthermore, in the illustrate embodiment the heat distribution unit is provided with a heating fluid pump P. The heating fluid pump P is configured to influence and control the flow of the heating liquid through the heating arrangement  100  and, thus, through the heating liquid circle. 
     It is to be noted that, in principle, the heating liquid can be replaced by any appropriate fluid. However, it is believed that the usage of a heating liquid is to be preferred for various technical reasons. 
     The second heat exchanging unit  40  is configured, as described above in detail, such that it is configured for heat exchange between the hot air/combustion gases from the heating unit  10  and ventilation air, for example from an indoor room of a recreational vehicle. 
     The above described configurations are merely preferred examples for implementations of respective components. They are not provided to limit the scope of protection defined by the appended set of claims but for illustrative purposes merely. A skilled artisan will be able to imagine various modifications of the above described configurations without contravening the basic idea of the present invention and/or leaving the scope of protection as defined by the appended set of claims. 
     Finally, it is pointed to the fact that the present embodiments refer not just to a specific heating arrangement  100  comprising a corresponding heating apparatus  1  and a heat distribution unit  60 , but also to the heat distribution unit  60  per se. 
     REFERENCE NUMERALS 
     
         
           1  heating apparatus 
           10  heating unit 
           12  primary housing 
           12   a  opening 
           12   c  ventilation slots 
           14  secondary housing 
           14   b  ventilation air outlet section 
           14   c  ventilation slots 
           16  coupling member 
           16   a  base portion 
           16   a   1  bearing surface 
           16   a   2  through holes 
           16   b  preheating portion 
           16   b   1  combustion air flow duct 
           16   b   1 A inlet opening 
           16   b   1 B outlet opening 
           16   b   2  exhaust gases flow duct 
           16   b   2 A first inlet opening 
           16   b   2 B second inlet opening 
           16   b   2 C outlet opening 
           16   b   3  separation wall 
           16   c  printed circuit board assembly (PCBA) coupling portion 
           16   c   1  threaded bore 
           16   d  first burner coupling portion 
           16   e  second burner coupling portion 
           18  printed circuit board assembly (PCBA) 
           20  first burner 
           20   b  nozzle 
           20   c  ignition arrangement 
           22  second burner 
           22   a  combustion air flow duct 
           22   a   1  inlet opening 
           22   b   1  first nozzle 
           22   b   2  second nozzle 
           22   c  ignition arrangement 
           22   d  controlling arrangement of the second burner 
           22   e  combustion area 
           24  fuel gas or liquid piping 
           26  combustion air fan unit 
           26   a  first housing element 
           26   a   1  combustion air inlet opening 
           26   a   2  first combustion air outlet opening 
           26   a   3  second combustion air outlet opening 
           26   b  second housing element 
           26   b   1  driving rod through hole 
           26   c  combustion air fan 
           26   d  combustion air fan driving unit 
           26   e  combustion air fan chamber 
           28  ventilation air driving unit 
           28   a  inlet opening 
           28   b  outlet opening 
           30  first heat exchanging unit 
           32  liquid tank 
           32   a  main body 
           32   a   1  bottom plate 
           32   b  lid member 
           32   b   1  exhaust gases inlet opening 
           32   b   2  exhaust gases outlet opening 
           32   b   3  cold liquid inlet opening 
           32   b   4  hot liquid outlet opening 
           32   b   5  first equipment insertion opening 
           32   b   6  second equipment insertion opening 
           34  exhaust gases piping 
           34   a  combustion chamber section 
           34   b  exhaust gases leading section 
           36  cold liquid piping 
           38  hot liquid piping 
           39  heating members 
           40  second heat exchanging unit 
           42  ventilation air enclosure 
           42   a  body portion 
           42   a   1  end plate 
           42   a   1 A ventilation air inlet opening 
           42   a   1 B exhaust gases inlet opening 
           42   a   1 C exhaust gases outlet opening 
           42   b  lid section 
           42   b   1  first ventilation air outlet opening 
           42   b   2  second ventilation air outlet opening 
           42   b   3  third ventilation air outlet opening 
           42   b   4  fourth ventilation air outlet opening 
           44  exhaust gases piping 
           44   a  combustion chamber section 
           44   b  exhaust gases leading section 
           50  heat exchanging units housing shell 
           50   a  first heat exchanging unit section 
           50   b  second heat exchanging unit section 
           52  supplementary mounting member 
           52   a  first heat exchanging unit section 
           52   b  second heat exchanging unit section 
           52   c  mounting section 
           60  heat distribution unit 
           70  third heat exchanging unit 
           80  hot liquid output device 
           90  external heating device 
           100  heating arrangement 
         P heating liquid pump