three basic air flows can be present in the solar furnace 10 . the first is the flow of conditioning air which becomes heated as it flows through the solar heat collecting units 18 and which then becomes cool as it delivers the heat to a storage medium within the interior of the solor furnace 10 . the second is the flow of utility air which transfers the heat stored in the storage medium into the building 12 . conditioning air flow and utility air flow operate independently of each other and are driven by separate air blowers . in practice , the conditioning air flow operates to bring the solar furnace 10 up to temperature and then the conditioning air flow and the utility air flow are operated alternately to maintain the building 12 and the furnace 10 at constant temperature . hot utility air flow is possible by operating the conditioning air blower and the utility air blower simultaneously . hot utility air flow delivers heat directly from the collecting units 18 to the building 12 . each type of air flow will be discussed in detail hereinafter . fig3 shows the solar furnace 10 with reflective panels 16 fully open and responsive to solar radiation input for directing the radiation to the collecting units . as solar radiation is directed into the collector units 18 either directly from the sun or indirectly from the reflective panels 16 or elsewhere , the solar radiation is trapped in collecting plates 36 located behind a single layer of glass 38 . the structure and use of such collecting plates 36 are fully disclosed in the aforementioned copending application for solar heat collecting units , ser . no . 515 , 230 . the collecting plates 36 , best shown in fig5 are adapted to be mounted upon a support surface 40 so that an inner plate portion 42 extends perpendicularly away from the support surface 40 and has an outer plate portion 44 forming an upwardly obtuse angle with the outer edge of the inner plate portion 42 . the collecting plates 36 may comprise any of the various embodiments disclosed in the aforementioned application for solar heat collecting units and a plurality of these collection plates 36 are mounted in spaced relationship to each other to cooperate in efficiently trapping and absorbing solar radiation in a manner so as to minimize radiative losses . since substantially all of the solar radiation received by the collecting plates 36 is absorbed , the double and triple pane glass previously found necessary in prior art solar furnaces to prevent solar radiation from escaping the collector is no longer needed . rather , a single pane of glass 38 can be used . the conditioning air shown in fig3 as dotted arrows 46 passes through the channels 48 defined in and between collecting plates 36 as best shown in fig5 . fig9 shows the flow of the conditioning air 46 in greater detail . conditioning air 46 enters a vertical delivery duct 50 at its lower base position 52 with part of the conditioning air traversing the entire length of the vertical delivery duct 50 and being delivered into an upper horizontal entry duct 54 , both the vertical delivery duct 50 and the horizontal entry duct 54 have one side 56 and 58 , respectively , open for uniform delivery of the conditioning air into the collecting plates 36 . for clarity of description , the orientation of fig1 is assumed and collector plates on the western , southern eastern and top surfaces of solar furnace 10 are designated as 36w , 36s , 36e and 36t , respectively . likewise , conditioning air flow 46 and other appropriate elements will be similarly referenced . consider first conditioning air 46w emanating from the open side 56 of the vertical delivery duct 50 . conditioning air 46w is uniformly distributed in the plurality of collector plates 36w along the entire vertical surface of collecting unit 18w . the conditioning air 46w flows through the solar heat trapping channels 48w picking up trapped solar heat and then into correspondingly joining and abutting trapping channels 48s . the conditioning air , now termed 46s , continues on its uniform flow through collector unit 18s and into adjoining and correspondingly abutting channels , not shown , on collecting unit 18e . the conditioning air 46e transverses the collecting channels 48e and is collected in a vertical return duct 60 by passage through an open side 62 . in similar fashion , a portion of conditioning air 46 is uniformly distributed into the collecting plates 18t through the open side 58 of horizontal delivery duct 54 and the conditioning air 46t traverses the collecting unit 18t and is delivered into an open side 64 of a horizontal return duct 66 . conditioning air 46t joins the conditioning air 46e for delivery to the interior of the solar furnace 10 at collection point 68 . it is evident that the exiting conditioning air 46 from the collector units 18 at collection point 68 is substantially hotter than the conditioning air entering the vertical delivery duct 50 at entry point 52 . this hot conditioning air is therefore ready to deliver heat to heat retaining material 80 in the storage chamber . conditioning air 46 is combined from collecting paths 46t and 46e for delivery into an upper screen duct 70 through an upward passageway 72 as shown in fig1 . the upper screen duct 70 comprises a longitudinally extending screen 74 having two semi - circular closed ends 76 . the upper screen duct 70 rests on a support baffle 78 and is completely covered along its longitudinal extent by the heat retaiing material 80 . it will be appreciated that the screen duct 70 is elevated relative to the collection point 68 so that after the hot air enters the screen duct 70 it is trapped in the storage chamber 94 in which the heat retaining material is confined due to the fact that hot air is lighter than relatively cool air . prior to entering the screen duct 70 , the conditioning air enters a mixing chamber 82 which is in fluid communication with the collection point 68 . in the present embodiment , the mixing chamber 82 is defined by an end wall 86 perpendicular to and in close fitting proximity to parallel baffles 78 and 79 . conventional angle supports 88 , or any other conventional support , may be used to firmly affix the end wall 86 to the upper and lower baffles 78 and 79 respectively . the end wall 86 isolates the heat retaining material 80 from the mixing chamber 82 . side walls 90 of the mixing chamber 82 are similarly affixed and seen best in fig1 . in fig4 and 8 , the conditioning air 46 can be seen to exit from the upper screen duct 70 uniformly along its elongated arcuate upper screened surface 74 and into the surrounding heat retaining material 80 . due to a series of alternately spaced baffles 78 and 79 , respectively , the conditioning air 46 weaves a downwardly reversing zigzag path passing uniformly through the heat retaining material and then finally exiting through the lower screen duct 92 . it is evident that the conditioning air 46 has full and complete access to substantially all surfaces of the heat retaining material 80 within the storage chamber 94 of the solar furnace 10 . in the preferred form , the heat retaining material 80 is a granite rock having a diameter in the range of 3 / 4inches to 11 / 2 inches so that the spaces between the rock particles are sufficient to allow the free flow of air through the storage chamber 94 . the longitudinal screen mesh for the upper and lower screen ducts 70 and 92 , respectively , is of smaller mesh size than the particle size of the gravel heat retaining material 80 so as to prevent the gravel heat retaining material 80 from falling into the ducts . it is obvious that any suitable heat retaining material can be used and that the size of the screen mesh can be varied accordingly . fig4 illustrates the detail flow of the conditioning air 46 within the storage chamber 94 . the conditioning air 46 emerges from the longitudinally screened surface 74 of the upper screen duct 70 and is forced to follow a downwardly reversing path among and between the baffles 78 and 79 . baffles 78 are in parallel spaced relation to each other and are mounted to the inner surface of the rear wall 96 . the remaining baffles 79 are in parallel spaced relation with each other and to baffles 78 and are mounted on the inner surface of the front wall 98 so as to extend between the baffles 78 . both sets of baffles 78 and 79 are mounted to the interior surfaces of the side walls 100 . fig5 illustrates one method of mounting the baffles 78 to front wall 98 and to side walls 100 . in this regard all baffles 78 and 79 are firmly fixed on three ends with the remaining end 102 being in spaced relation to an opposing rear or front wall . angle iron 104 is used in the present invention to firmly attach the baffle 78 to the front wall 98 and to the side wall 100 . the angle iron 104 is diagrammatically shown in fig4 , and 11 . the angle iron 104 may be affixed by any conventional means such as screw - type fasteners . the downwardly reversing path which the conditioning air 46 follows causes the hot air to pass through the heat pretaining material 80 in such a manner as to come into contact pwith substantially all of the heat retaining material located within the storage chamber 94 . it should be realized that the heat retaining material surrounding the upper screen duct 70 will normally be substantially hotter than the heat retaining material around the lower screen duct 92 since the conditioning air 46 becomes cooler as it passes downwardly through the storage chamber 94 loosing its heat to the heat retaining material . this , of course , is subject to the proviso that the conditioning air temperature as it comes from the collector units 18 is higher than the temperature of the heat retaining material 80 found within the storage chamber 94 . the conditioning air 46 exits the storage chamber 94 by uniformly entering the arcuate longitudinal screened surface of the lower screen duct 92 . referring now to fig1 , it will be seen that the conditioning air 46 is collected and forced through a blower 106 which is driven by motor 108 positioned rearwardly to the blower 106 and is driven through a lower exit duct 110 and then upwardly into the vertical delivery duct 50 . the lower exit duct 110 operates in the same fashion as the mixing chamber 82 did at collection point 68 . thus , the cooler conditioning air 46 , having given up its heat to the heat retaining material 80 , seeks a lower level than corresponding hot air . this prevents the passage of any hotter air downward through the vertical deliery duct 50 and into the lower screen duct 92 when the blower 106 is not operating . this eliminates the need for expensive valve - like devices to prevent such air flow . the conditioning air 46 being forced by the blower 106 through the vertical deliery duct 50 is now ready for delivery into the collecting units 18 for beginning another cycle . the conditioning air 46 intermittently recirculates in this fashion first passing over the collecting units 18 to become heated and then into the storage chamber 94 delivering that heat into the heat retaining material 80 found within the storage chamber 94 under the forcing pressure of the blower 106 . fig2 and 11 show the utility blower 112 driven by motor 114 which forces the utility air 116 designated by arrows from a vertical utility deliery duct 118 into the building 12 via delivery pipe 24 for delivery into the conventional forced air heating system , not shown . it can , therefore , be appreciated that a circulating utility air flow 116 is established by means of a utility air blower 112 whereby hot air can be drawn , in a manner subsequently shown , from the storage chamber 94 and blown into the building structure 12 wherein it may be selectively diverted through various vent openings into desired locations in the building structure for heating . cool utility air 116 returns from the building structure 12 via return pipe 26 and into the return housing 34 as illustrated in fig2 and 7 . the return housing 34 can be of any conventional structure that surrounds the return pipe 26 as it enters an upwardly extending inlet duct 120 , fig7 . the return housing 34 insulates the storage chamber 94 from heat loss to the ground and prevents instrusion by insects , animals , and the like . it is evident that since the return pipe 26 is below the bottom level of the storage chamber 94 and the delivery pipe 24 the need for an expensive valve is eliminated . heat in the storage chamber 94 naturally rises and , therefore , hot air in the storage chamber 94 would not seek a path from the chamber 94 to the return pipe 26 . the returning cool utility air 116 is forced to follow an upwardly reversing path , fig7 through the heat retaining material 80 until it reaches an exit duct 122 . the utility air 116 as it passes through the heat retaining material 80 in the upward direction becomes increasingly hotter until at the exit duct 122 the utility air is at its maximum temperature . during delivery of utility air 116 , the conditioning air blower 106 is normally inoperative and there is not conditioning air flow . however , hot air 124 from the upper regions of the storage chamber 94 can enter the utility air flow 116 as shown in fig7 . the utility air 116 passing through the exit duct 122 , also shown in fig1 , is delivered through a vertical delivery duct 118 into the utlity air blower 112 and thence into the building 12 . as will be appreciated by reference to fig7 and 11 , the utility air 116 does not have the uniform flow through the heat retaining material 80 that the conditioning air 46 has . essentially , the utility air 116 enters from a point source , i . e ., the inlet duct 120 , and exits into a point sink , i . e ., the exit duct 122 . the primary path followed by the utility air 116 is one that is upwardly reversing through the baffles 78 and 79 but which essentially follows a diagonal path direction 116a as shown in fig1 . of course , as the utility air 116 travels the upwardly reversing diagonal path 116a dispersion 116b occurs causing greater access to the heat retaining material 80 . as the utility air 116 heats the building 12 , there is a heat loss in the storage chamber 94 . the greatest concentration of the heat loss occurs within the heat retaining material 80 positioned along the diagonal path 116a with its associated dispersion paths 116b . as this region of the heat retaining material 80 becomes cooler , inward convection indicated by arrows 116c will deliver heat from the outer regions of the heat retaining material 80 to the material along the diagonal path 116a . in this manner heat stored within the storage chamber 94 is depleted in a fairly uniform manner and delivered into the building 12 . hot utility air flow is different from normal utility air flow in that hotter air is provided by the solar furnace 10 to the building 12 than provided by the normal utility air flow 116 . this is illustrated in fig6 and occurs when the conditioning air blower 106 and the utility air blower 112 are operating in the same time period . in this mode , the conditioning air 46 enters the storage chamber 94 from the upper screen duct 70 and is delivered after one reversing path directly into the vertical delivery duct 118 as hot utility air indicated by arrows 126 . the hot utility air 126 is now delivered in the same manner as the utility air 116 into the building 12 and then redelivered for reheating through inlet duct 120 where it passes almost immediately into the lower screen duct 92 as conditioning air 46 . in this mode of air transfer , the bulk of the storage chamber 94 is bypassed . the conditioning air 46 , as it enters from the collecting units 18 , is delivered through the hottest portion of the storage chamber 94 and directly into the building 12 as hot utility air 126 . this provides the building 12 with an initial surge of very hot air , such as is needed , for example , when initially warming the building up . such air flow , of course , is not useful on overcast days or the like . the preferred method of heating is found in fig4 and 7 wherein the solar heat is first stored within the storage chamber 94 for later delivery into the building 12 . the method as shown in fig6 generates an initial surge of heat while the sun is directly on the solar furnace 10 , but , as mentioned , is susceptible to cloud cover . as best shown in fig5 insulating panels 130 are used for isolating the collecting units 18 from the storage chamber 94 . the framework for the storage chamber 94 includes three insulating rectangular panels 130 of substantially the same size which are interconnected along their longitudinal edges to form when connected to two insulating end panels an elongated housing of rectangular transverse cross - section with a closed top . a fourth similarly constructed rectangular panel 131 forms the bottom of the storage chamber 94 and is large enough to also form the bottom of the side collecting units 18w , 18s and 18e as best illustrated in fig4 . each of the panels 130 and 131 is laminate with conventional plywood sheets on opposing faces with an inner relatively thick core of insulating material such as a rigid polyurethane foam . these panels are preferably painted or coated with a reflective paint such as silver paint to better retain heat within the storage chamber . the panels are interconnected in a conventional manner . the solar reflective panels 16 are conventionally hinged to the edges of the bottom rectangular panel 131 to allow complete closure over the collecting units 18 in order to protect the single pane of glass 38 from detrimental environmental elements such as hail , sunlight in the summer months , and the like . the glass 38 receives structural support from dividers 132 which also reduces the cost of the glass due to the smaller glass panels used . one feature in having spaced parallel baffles 78 and 79 , in addition to providing uniform distribution of heat , is to uniformly and significantly reduce the lateral pressure on the side panels 130 of the solar furnace 10 . fig4 illustrates lateral side stress vectors 142 of the present invention . generally , the weight of the heat retaining material 80 is uniformly distributed on the upper surface of each baffle 78 and 79 . each baffle is firmly affixed on three ends as previously discussed with the fourth end 102 being unsupported . the bulk of the weight of the heat retaining material 80 , therefore , is absorbed by the side panels 130 where each baffle is firmly affixed . the side panel 130 opposite the open end 102 of a baffle also endures a stress as shown by stress vectors 142 since effectively two layers of heat retaining material 80 exert lateral side pressure on that portion of the side panel . in this manner , the heat retaining material 80 uniformly distributes corresponding lateral side wall pressure and vertical side wall pressure on the baffles 78 and 79 . such a structural arrangement is a considerable advantage over a natural piling of heat retaining material 80 within the storage chamber 94 . if no baffles were used , for example , the heat retaining material 80 would cause considerable lateral side pressure especially at the bottom of each side panel . thus , in a natural pile configuration , considerable structural strength would have to be provided along the bottom edges of the side panels of the storage chamber 94 . thus , in the present invention , the provision of parallel spaced alternating baffles 78 and 79 which provide uniform utility and conditioning air distribution to all surfaces of the heat retaining material 80 further lend considerable structural support to the storage chamber 94 . the provision of these baffles provides uniform distribution of lateral side forces from the upper level to the lower bottom portion of the side walls . although the present invention has been described with a degree of certain particularity , it is understood that the present disclosure has been made by way of example , and that changes in detail of the structure may be made without departing from the spirit thereof .