WO1979000113A1

WO1979000113A1 - Forced air heating unit

Info

Publication number: WO1979000113A1
Application number: PCT/US1978/000005
Authority: WO
Inventors: C Buckner
Original assignee: C Buckner
Priority date: 1977-08-26
Filing date: 1978-06-05
Publication date: 1979-03-08
Also published as: GB2036943B; GB2036943A; EP0006897B1; SE7903684L; CH625329A5; EP0006897A1; CA1115611A

Abstract

A free-standing unit (10) for heating air in a U-shaped channel (18, 20, 22) surrounding a fire box (12, 78, 80, 82, 84) having a pair of spaced vertical vents (30, 32) for directing the heated forced air to converge in front of the fire box opening (34) to limit air flow towards said openings. Mesh (31) in the vertical vents (34) directs the forced air downward to be combined with the hot forced air from a bottom horizontal vent (88). A baffle plate (126) depending from the top of the fire-box adjacent the flue port (26) and an opening along the top of the doors ignite the gases adjacent the top and direct some gases back into the fire. By forcing heated air at a low level and drawing cool air from a high level, the air being heated is of a uniform temperature. A hood (66) extending along the top edge of the fire box opening diverts exiting gases back into the fire box. A thermostatically controlled blower (71) creates the forced air and cools the fire box walls.

Description

Description FORCED AIR HEATING UNIT

Technical Field

The present invention relates generally to heating units and more specifi¬ cally to a free standing heater using forced air.

Background Art

With the energy crisis a great concern, people have generally been preoccupied with maximizing the use of cheap and inexpensive fuels. A major effort has been made to include heat collectors in fireplaces to collect the heat normally generated by the wood burning therein and to transmit it into the room more efficiently than that provided by the normally designed fireplace. A forced air system in combination with such heat collectors is shown in U.S. Patent 3,896,785.

Even before the energy crisis, people were concerned with the loss of heat escaping through the flue of a heating source. Patents 1,490,135 and 3,094,980 make use of the flue heat in a stove and fireplace respectively to heat a second column of forced air which is introduced into the room in which the stove or fireplace is located.

Prior art space heaters have also been used or converted to fireplaces to provide a pleasing and second mode of heating. An example of this is shown in Patent 1,944,626.

Although showing many methods of recapture of heat loss by normal fireplace or space heaters, the prior art has not made the most effective use of the heating source. By concentrating their efforts on hotter fires or recapture of flue gases, the prior art has not effectively captured the heat available from the burning material. No effort is made to limit air flow to the fire and up the flue of a fireplace or open ire box except in closed systems with small intake vents.

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.fa wipo Thus there exists a need for a system of limiting air flow into the fire box and up the flue for open fireplaces or fire boxes.

Heating units of the prior art have either used the natural upward flow of heating air by drawing cold air in at the bottom of a heating unit to exit heated from the top. Also, forced air systems have been used to augment the natural upward flow by moving more air past the exterior of the fire box. Although the forced air systems have increased the capture of available heat, the prior art devices have not optimized the heat transfer from the burning material in the fire box to the air circulated about the exterior of the fire box.

The natural flow of drawing cold air in the bottom and exiting hot air from the top or just exiting hot air from the top (naturally or forced) creates a hot layer adjacent the top of the room and a cold layer at the floor. Thus there exists a need for a heating unit which maximizes the capture of heat available in burning material and which provides a more uniform temperature in the room.

The build-up of deposits on the exterior of the fire box in prior art devices result from incomplete combustion of the gases from the burning material. These deposits reduce the thermal convection of the heat in the ire box through the fire box wall. Similarly, the loss of these gases up the flue is a loss of an available source of combustion and additional heat.

Thus there exists a need for a fire box which increases heat and reduces deposits.

Another problem with heating units of the prior art is the escape of smoke and other gases drawn from the fire box by the pressure differential produced by rapidly opening the doors of the fire box.

Disclosure of Invention

The present invention is a forced air heating unit having double walled sides, back, and bottom, and a single walled front and top. A forced air channel, defined by the double sides, back and bottom wall, includes a system of baffles to direct forced air over substantially all of the surface area of the side, back, and bottom fire box walls. The baffles in the back portion of the forced air channel direct forced air between the back portion and the two side and bottom portions. The baffles in the bottom portion direct forced air between the bottom portion and the back and two side portions. The baffles in the side direct forced air between the side portions and the back and bottom portions.

A blower is thermostatically controlled to introduce forced air into the air- channel for maintaining the back, side and bottom fire box walls in a minimum temperature range to heat the forced air while maximizing the transfer of heat from the burning material to the forced air channel instead of up the flue.

The front wall of the heating unit includes an access opening and a pair of doors for covering the access opening. An adjustable draft valve in each door includes a positive screw lock. Depending from the top of the fire box adjacent the flue port in the rear of the fire box is a gas baffle for directing rising gas to an area of the fire box where the gases are ignited. The gas baffle directs some of the gas downward to the burning material to be ignited and maintains some of the gases adjacent the top of the fire box in front of the gas baffle. The top of the doors are spaced from the top edge of the access opening to allow air to circulate into the firebox adjacent the top wall for aiding ignition of the gases collected adjacent the top wall. The major source of air is the space between the doors which is covered by a vertical strip mounted to one of the doors. A hood is mounted adjacent the top edge of the access opening for directing gases exiting the top edge of the access opening back into the fire box.

For an open fireplace or fire box, a draft system, including two vertical forced air channel exit vents adjacent the side edges of the access opening for creating hot air drafts which converge at a select eed distance in front of the access opening, limits the draft of air into the access opening. The converging hot air is effected by vertical deflection surfaces including vertical baffles in the side portion of the forced air channel or pneumatic surfaces produced by a lip extending across the vent opening or by the vent opening being offset from the exterior edge of the forced air channel. The less than ninety degree angle that the side walls form with the front of the forced air channel also aids the deflection. A mesh having inclined horizontal surfaces covers the vertical vents and directs the exiting air downward to be combined with heated forced air exiting horizontal vent in the front of the bottom portion of the forced air channel. The heated forced air from the two vertical vents and the horizontal vent pneumatically create a finite cool air pocket in front of the access opening to limit the amount of cool air available for the fire box.

The forced air heating unit uniformly heats a room by introducing forced hot air adjacent the floor of the room by the horizontal vent and the downward directing vertical vents. The forced air device mounted to the rear of the free¬ standing unit draws air from above and around the sides of the unit and around the space defined by the exiting forced hot air. The width of the side portion of the forced air channel tapers from the wider rear portion to the front to increase the air intake. Gravity lock door handles are provided on the access doors.

Brief Description of Drawings

Figure 1 is a front perspective view of a forced air heating unit employing the principles of the present invention.

Figure 2 is a partial cross-sectional view of the draft valve taken along lines π-π of Figure 1.

Figure 3 is an exploded, partial perspective view of the relationship of the top of the doors to the fire box opening.

Figure 4 is a partial side view illustrating the function of the hood according to the present invention. Figure 5 is a rear cutaway perspective of the forced air heating unit illus¬ trating the baffle system.

Figure 6 is a front partial perspective of the bottom, back, and side walls of the forced air heating unit illustrating the baffle system.

Figure 7 is a perspective schematic of the heat flow in the fire box.

Figure 8 is a side cross-sectional view illustrating gas circulation in the fire box.

Figure 9 is a front perspective of a fireplace employing the principles of the present invention.

Figure 10 is a side view illustrating the forced air pattern according to the principles of the present invention.

Figure 11 is a plan view illustrating the forced air pattern according to the principles of the present invention.

Figure 12 is an enlarged plan view of a vertical vent illustrating the deflect¬ ing principle of the present invention.

Figures 13 and 14 are enlarged plan cross-sectional view of alternative embodiments of vertical deflectors.

Figure 15 is a front view of the mesh used in the vents.

Figure 16 is a cross-sectional view taken along lines XVI-XVI of Figure 15.

Figure 17 is a schematic of the air circulation produced by the present invention.

Figure 18 is a front view of another embodiment of the principles of the present invention.

Figure 19 is a perspective of another embodiment of the present invention.

Best Mode for Carrying out the Invention

Figure 1, which illustrates a preferred embodiment of the forced air heating unit 10, shows a housing having top, front, bottom, two sides, and back walls, 12, 14,

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OMPI 16, 18, 20, and 22 respectively. Top wall 12, which is a single walled portion of the housing, extends past the front, back, and side walls, and includes a collar 24 sur¬ rounding an orifice or flue port 26. A flue (not shown) to remove the fumes from a source of heat or combustible material is connected to flue port 26 through the collar 24. The heating unit 10 is supported by four legs 28 providing space betweeen the floor and the bottom wall 16. Front wall 14 has a pair of elongated vertical vents 30 and 32, each covered by a screen 31 which is secured to the front wall 14 by a bracket or lip 33.

An access opening 34 in front wall 14 is covered by a closure including a pair of doors 36 and 38. The vertical vents 30, 32 extend substantially the height of the opening 34 and are spaced from the bottom and top of the opening 34. The door 38 has a strip 40 which overlaps door 36 and holds door 36 closed and covers the space between the adjacent edges of the doors.^' Handle 42 on door 38 is connected to a latch 43 which engages the top interior portion above the opening 34 so as to lock the doors closed. The handle 42 rotates down to close, thus providing a gravity lock of the doors. A pair of posts 41 and 45 on the interior of the doors 38 provides tops for latch 43. Post 41 may be mounted to the interior of front wall 14 if desired.

Also provided on doors 36 and 38 are a pair of draft valves 44 and 46. The sliding portions 50 and 52 of draft valves 44 and 46 slide within guide members 54 and 56 to adjust the size of a plurality of elongated openings 48 in doors 36 and 38. When a fire is provided in the interior chamber of housing 10, the slides 50 and 52 adjustably vary the draft valves 44 and 46 to regulate the amount of air or draft introduced into the chamber and are locked in the adjusted position by threaded knobs 51 and 53 respectively engaging the face of doors 36 and 38 respectively as illustrated in Figure 2. For a wood burning souree of combustible material, this would vary the rate of burning as well as the temperature. These valves are used in conjunction with an adjustable flue port 26. Although the draft valves 44, 46 are shown in the doors 36, 38, they may also be used on a front wall of the fire box below the doors if such a surface is made available. The doors 36 and 38 are mounted to the housing by upper hinges 58 and 60 and lower hinges 62 and 64, re¬ spectively. The doors and hinges are dimensional so that the bottom of doors 36, 38 rest flush against the front wall 14 and the top of doors 36, 38 are spaced from the front wall 14 at the top edge of opening 34 as illustrated in Figures 5 and 19. The importance of this separation will be discussed below in reference to Figures 3 and 8.

Also mounted to the front wall 14 is a hood 66 and a platform 68. The hood 66 traps any smoke pulled from the fire box at the upper edge of access opening 34 when the doors 36, 38 are rapidly opened and directs it back into the fire box as illustrated in Figure 4. The hood 66 includes a center portion 65 and a pair of side portions 67 for capturing the escaping gases and directing them back into the opening 34. The platform 68 provides a surface for supporting a fireplace screen when the heating unit 10 is used as a fireplace without doors.

The forced air system includes a source of forced air, a channel, a baffle system, and deflectors. The source of foreed air, including a housing 70, is mounted to the back wall 22 and includes an opening 72. Located within the housing 70 is a blower 71 or any other system which will receive air through opening 72 and provides a forced air flow within the channels to be described. A thermostatic control 73 is mounted in rear wall 22 (Figure 6) and controls the operation of' fan 71 based on the temperature of the air in the forced air channel. Housing 70 may also contain a source of moisture which is illustrated in Figure 5, for example, as a pan 74 having water therein. The pan of water is merely one example of a source of moisture. Forced air housing 70 communicates with the forced air channels via an inlet 76 in the back wall 22.

Although the location of inlet 76 and blower 71 on the back wall is preferred for most applications, they may be located any place which provides them access to the forced air channel. For example, inlet 76 and blower 71 could be on either side wall 18, 20 or on top 12 over the back or either side portion of the foreed air

OMPI ,fa W1PO channel. Similarly, they may be on the front wall 14 with access to the two side o bottom portion of the forced air channel.

The air channel of the present device includes the exterior sides, back, an bottom walls 18, 20, 22, and 16 respectively and interior sides, back, and botto walls 78, 80, 82, and 84 respectively. The sides and back walls of the housing an the sides and back interior walls form a generally U-shaped forced air channel wit the side walls at an angle other than ninety degrees relative to the back where th forced air from opening 76 is transmitted towards front vents 30 and 32. Th separation of the side walls 18 and 78 and 20 and 80 or the width of the side force air channel tapers or diminishes from the rear to the front. The increased width o the back air channel and the rear of the side air channel allows blower 71 to pum more air per minute into the foreed air channel. The forced air from opening 76 i also provided from the rear forced air channel through an opening 86 into th forced air channel formed by the housing and the interior bottom walls to exi through horizontal vent 88, illustrated in Figure 6, in the front portion of th bottom air channel. The air in the bottom foreed air channel also exits into th side forced air channels. Thus it can be seen that forced air traverses substantiall the total surface of the interior back, side, and bottom walls.

Within the forced air channels are baffle systems to create specific ai patterns which diverge from the forced air source at opening 76 and converge o the respective vents in the front of the air channels. The rear wall portions of th baffle system includes a horizontal baffle 90 substantially bisecting opening 7 from the forced air system. Also provided in the rear wall are two upper baffles 9 and 94 and two lower baffles 96 and 98 which diverge from the foreed air openin 76. Baffles 94 and 96 direct divergent air flow towards one side wall channel whil baffle 92 and 96 in combination direct diverging air flow toward the other side wal channel. Upper baffles 92 and 94 direct an upward flow towards the respective sid wall channel portions and baffles 96 and 98 provide a flow towards opening 86 int the bottom foreed air channel as well as providing a small flow to the respective side forced air channel.

Located in each side forced air channel are baffles 102, 104, 106, and 108, and in bottom forced air channel are baffles 112, 114, 116, 118, 120, 122, and 124. The inner ends of bottom baffles 114, 116, 118, and 120, 122, 124 are offset relative to the center bottom baffle 112 so as to divert varying portions of the air flowing towards bottom vent 88 and to direct it towards side wall baffles 102 and 104. The angle and location of baffles 114, 116, 118, 120, 122 and 124 are such that the air between baffles 114-116 and 120-122 is directed toward the lower face of side baffle 102j and the air between baffles 116 and 122 and the rear of the bottom is bisected by baffles 118 and 124 respectively and directed between baffles 102 and 104. Since the source of the temperature modification is generally placed adjacent interior bottom wall 84, the communication of the air flow from the bottom forced air channel to the side forced air channel increases the efficiency of the temperature transfer.

The specific design of the baffles and their location assures that the air traverses substantially all the interior walls and thereby allows a greater heat transfer from the interior or fire box to the forced air without sacrificing the head of the air emitting from the vents 30, 32, and 88 since it cools a greater surface area. Prior art devices generally substantially increase the length of the air path while sacrificing the head of the air at the vents and thereby reducing the heat transferability of the interior walls. The baffle system in the walls produce streams of air which are not troubled by eddy currents, dead air pockets, localized hot spots, and other disadvantageous features of the prior art systems.

Blower 71 is chosen to have sufficient capacity to force air in the air channel at a sufficiently high velocity to lower the temperature of the interior walls and thereby increase the transfer of heat from the fire box to the interior walls to be removed by the forced air. Thus less heat from the fire box is available for transmission up the flue. For a heating unit eighteen inches high without legs by twenty-three inches wide at the front by fourteen inches deep, a blower having a

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OMPI r Λ ^■fa. W1PO _tΛ, capability of pumping 140 cubic feet of air per minute is sufficient. A blower pushing 465 cubic feet per minute is adequate for a unit twenty-seven inches high by forty-two inches wide by twenty inches deep.

' An analysis of the thermodynamics of the heating unit 10 will substantiate the efficiency or maximization of heat transfer or capture of the unit. The formula for representing the heat transferred from the heated air in the fire box through the interior walls to the forced air in the forced air channel is:

Q = A U Δ T where Q= heat transferred in BUT/hour;

A= effective heat-transfer surface area perpendicular to the direction of heat flow in feet square; jb, T= mean temperature difference between the forced air and the fire box air in degrees fahrenheit;

U= overall heat-transfer coefficient in BTU/(hour)(feet) (°F) The overall heat transfer coefficient Q is a function of the resistance to the flow of heat of (a) the air in the fire box, (b) the firebox wall, (c) the forced air, and (d) the fouling on each side-of the fire box wall.

One way to maximize the transfer of heat is to create as great as possible temperate differential T. The blower 71 in combination with thermostat control 73 maintain the back, two sides, and bottom wall of the fire box in a range of temperature to maximize the heat transfer through the fire box walls while heating the forced air to a sufficiently warm temperature. For example, thermostat 73 could turn blower 71 on once the temperature in the forced air channel is 115° F. and turn the blower 71 off when the forced air temperature is reduced below 100° F. If desired, the thermostat control 73 could vary the speed of blower 71. The preferred range is 95° F. to 150° F.

By forcing air over substantially all the back, two sides, and bottom fire box walls, heating unit 10 substantially maximizes the effective surface area A at the

' O greatest temperature differential. This area could be further increased by extending the forced air channel over the top wall 12 of the fire box, if desired, but is not preferred.

The heat flow within the fire box is also based on the above equation except that the temperature differential A T should be expressed as a temperature gradient or the change in temperature per unit distance. The amount of heat flow is illustrated in Figure 7 by the length of the vector. Since the bottom forced air channel, being the closest cool surface, has the largest gradient or vector D. The forced air cooled two side and back walls, being substantially equidistant from the fire, have the next largest vectors L,R, and B, respectively. The front wall, being a non-forced air wall, can only cool by heat dissipation. Thus, the temperature gradient toward the front wall, and consequently the heat flow F, is substantially less than those toward the forced air cooled walls. Similar to the front wall, the top wall is not forced air coof and thus has a small heat flow U. Since gas ignition occurs adjacent the top (as will be discussed for Figure 8), the surface of the top wall is even hotter than the front wall and consequently vector U is smaller than vector F. With a limited air flow up the flue, there is very little heat left to exit the flue port as illustrated by vector O.

Thus the thermostatically controlled blower maximizes the surface area of maximum temperature differential to effectively capture or draw eighty percent of the heat available from the fire box into the forced air channel. This is comparable to the heat efficiency of a residential furnace.

To maximize the heat transfer coefficient of the unit 10, a device is provided to reduce the build-up of deposits on the fire box wall by igniting the rising gases from a wood fire. This ignition also increases the amount of heat available from the wood. This device includes a gas baffle 126 extending down from the top wall 126 adjacent the flue port 26 as illustrated in Figure 8.

With the doors 36, 38, closed, the slide drafts 44, 46 on the doors allow a controlled, even flow of air across the fire. As the wood is burned, the unburned gases rise from the fire up and slightly forward, to the top wall 12. As they contact the top wall 12, they circulate to the rear of the fire box, toward the flue port 26 and contact baffle 120 which deflects the gases downward. At this point, some will go under the baffle 126 and out the flue port 26, some will be pulled back into the fire and reburned, and some will be recirculated at the top 12 by the gases rising from the fire.

Approximately 30 seconds after an even fire has been established, a rolling cushion of smoke (partially burned gases) will build up under the top wall 12. This cushion acts to hold the resins and gases in the fire to burn longer and holds the gases in the fire box until they are recirculated and burned as completely as possible.

As the wood gases rise away from the fire, they cool quite rapidly. In order to prevent the cooling gases from liquefying and building up creosote deposits inside the fire box, and later in the chimney, a small amount of secondary air is injected at the top of the doors 36, 38. The secondary air injection ignites the gases directly under top wall 12. This secondary burning action more completely burns the gases and raises the temperature of the smoke escaping up the chimney sufficiently to prevent the solids in the smoke from separating and building up inside the chimney. This action also raises the temperature of the top wall 12 to cooking level.

The space between the two doors 36 and 38 and the mounting of the doors 36 and 38 soTfiat the top edges of the doors are spaced from the top edge of the access opening 34 permits the secondary air flow into the area adjacent the top wall 12 aiding the ignition of gas collected there. Although the air space is provided by the tops of the doors being offset from the plane of the front wall 14, this space may also be provided by making the top of the doors shorter than the access opening 34.

The forced air heating unit 10, as illustrated in Figure 9 may be used as a free standing fireplace. The doors 36 and 38 are removed and a screen 128 is provided underneath hood 66 and resting on platform 68. The screen may be a typical fireplace screen to prevent sparks and ashes from emitting from the fireplace and causing a fire hazard within the room. Adjacent to and surrounding openings 34 is a rim 130. Four pins 132 of hinges 58, 60, 62, 64 are provided on the rim 130 as well as four openings 134 in the rim. The matching hinge element of the closures 36, 38 move in and out of the openings 134 in the rim 130. In addition to providing the pin portion 132 of the hinges for the closures 36 and 38, the rim 130 provides a guide and retainer for the screen 128 which fits within the rim 130. Though not shown, the rim 130 extends above and across the top of the opening 34. A pair of andirons 136 are provided in the interior chamber to support the source of temperature modification. It should be noted that grating or other supports may be used instead of andirons 136.

The forced air heating device 10 includes a system of deflectors at the vertical vents 30 and 32 to define a unique air flow pattern in front of the fire box opening 34. As illustrated in Figures 10 and 11, the heated forced air (dashed lines) from vertical vents 30, 32 are directed towards each other to converge in front of the fire box opening 34 a preselected distance. This creates an air pocket 140 in front of the fire box opening 34 in combination with the heated forced air exiting the bottom horizontal vent 88 which is illustrated in Figure 10 but deleted from the pattern of Figure U for. sake of clarity. The pneumatically created barrier for air pocket 140 limits the amount of air from which the fire can draw and thereby reduces the rate of combustion in the fire box. Also, the outward moving heated air reduces cold air drafts toward the access opening 34. The U-shaped pneumatic barrier is a critical substitute for the open or removed doors 36 and 38.

The major source of cool air (solid lines) for the pocket 140 in front of the fire box is the triangular aerodynamic openings 142 between the bottom of the vertical vents 30, 32 and the forced air from the horizontal vent 88. The forced

OMPI hot air from vertical vents 30, 32 also is directed downward, as well as inward converge, allowing air to flow into the pocket 140 over the top edge of the fre hot air V. The two vertical air streams converge preferably at about five feet front of the access opening. To converge much closer would draw smoke from t fire box.

Blower 71 on the back wall draws air as indicated by the solid lines arou the sides of the unit and over the top. Thus the cool or return air flow is outsi the air pattern defined by vents 30, 32 and 88 which pneumatically block cool a flow into the fire box.

A preferred device for directing the air exiting the vertical vents 30 and to converge is illustrated in the enlarged view of Figure 12. The side walls 18 a 78 are mounted to the front wall 14 at an opening 144 in the front wall. While si wall 78 lies at the edge of the opening 144, side wall 18 is slightly offset. Th offset may be eliminated. The side walls 18, 78 form an angle less than nine degrees with the front wall 14 to aid the deflection of forced air inward. T bracket 33 is generally L-shaped having a portion extending across the opening 14 The bracket 33 forms an air pocket along the outside edge of opening 144 which is pneumatically produced deflection surface 146. The pneumatic deflection surfa exterior the forced air channel is sufficient to direct the heated forced air converge in-front of the fire box access opening 34.

Two alternative embodiments are illustrated in Figures 13 and 14. In lieu the external pneumatic deflector 146, an internal pneumatic deflector could used. As shown in Figure 13, the exterior side wall 18 is substantially offset fro the edge of opening 144 providing a pneumatically produced deflection surface 14 Figure 14 shows a vertical deflection plate or baffle 150 mounted between t exterior side wall 18 and front wall 14. The side forced air channels form a nine degree angle with the front wall, although the non-ninety degree angle alignment preferred. Each embodiment may also include the pneumatical deflection surfa 136 produced by the L-shaped bracket 33.

The downward air flow is produced by the mesh 31 secured to the L-shaped bracket 33 across vent opening 144. As illustrated in Figures 15 and 16, the mesh 31 includes a plurality of horizontal surfaces 152, at the intersection of adjacent openings, inclined downward from the back to the front to deflect air downward without retarding the air flow through the mesh 31. If the downward deflection is not required, mesh 31 may be mounted with the surfaces 152 vertical to provide the converging air flow. Basically, the mesh 31 may be mounted with any desired orientation of the surfaces 152 to produce a correspondingly directed air flow (e.g. 45° angle relative to the horizontal).

The forced hot air patterns converging just off the floor in front of the unit push the cool air across the floor. When the forced air strikes a wall, it is deflected to either side and up. At the same time, the blower 71 is pulling return air to either side and down over the top of the unit. Thfc push-pull action results in a high volume of air movement as the blower system forces hot air across the floor and returns cool air around either side and overhead. This is exactly the opposite of normal air movement within a house and results in a more uniform temperature from floor to ceiling. The air patterns are illustrated in Figure 17 where the solid lines represent cool air and the dashed lines represent warm air.

A thermostat 154 may be provided in the room to be heated. Whereas thermostat control 73 preferably turns the blower on and off as a function of the air temperature in the forced air channel, thermostat 154 varies the speed of the blower as a function of the air temperature in the room to be heated. The use of a room thermostat increases the comfort in the room, but reduces the efficiency of the unit 10 since the fire box walls may not be kept at the lowest possible temperature.

Although the vertical units 30 and 32 are preferred so that the heating unit 10 could be used as a fireplace or operated with the doors open, they may be eliminated. The flow pattern of Figure 17 may also be produced by using only vents

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OMPΪ in the front of the bottom forced air channel. As illustrated in Figure 18, two additional vents 156 and 158 are provided on each side of vent 88. The pushing of warm air adjacent the floor and pulling cool air from above evenly heats the room.

The heating unit 10 could also be used as a furnace. As illustrated in Figure 19, top vents 160 and 162 may be connected to the plentum or duct system to be transmitted throughout a house. In either of these two embodiments, the baffle system is modified so as to direct air over the substantially all the surfaces and towards the vents without orming dead air pockets in the forced air channel.

Although reference has been to wood fires, the heating unit 10 is effective for use with coal, oil, gas, or any other heat source in the fire box.

Preferred method of assembly of the forced air heating unit 10 is to form the exterior side and back walls 18, 20, and 22, out of a single piece of material and the interior side- and back walls 78, 80, and 82 also out of a single piece of material. The baffles are mounted to the exterior side and back walls and the interior side and back walls are mounted to the baffles preferably by welding. The bottom exterior wall 16 is welded to the exterior side and back walls 18, 20, 22, and the baffles of the bottom forced air chamber are mounted to the bottom exterior wall. The bottom interior wall 84 is then joined to interior side and back walls 78, 80, 82. The top and front walls are then mounted to the structure by welding. The welding bead formed'between the top and the side and back walls provides a thermal barrier or guard such that the portion of the top 12 which extends beyond the side and back walls is cooler than a portion of the top which is directly over the fire box. The remaining elements are attached or mounted to the front wall and the forced air unit mounted to the rear wall.

It is suggested that the interior side and back walls 78, 80, and 82 be made of 3Λ6 inch thick steel and the exterior side and back walls as well as the top and front walls be made of 1/8 inch thick steel. The bottom exterior and interior walls may be made of 3Λ6 inch steel. The selection of different thicknesses of steel provides for a maximum absorption of the heat of the interior chamber as a heat exchanger to be used in contact with the forced air which cools the interior walls while taking advantage economically of thinner exterior walls.

From the preceding description of the preferred embodiments, it is evident that the objects of the invention are obtained. A forced air heating unit is provided which maximizes the use of available heat from a fire box by a unique thermostatically controlled forced air system including pneumatically produced surfaces and barriers. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation. The spirit and scope of this invention is to be limited only by the terms of the appended claims.

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Claims

1. A forced air heating unit comprising: a chamber for holding a source of heatj an opening in the front wall of said chamber for providing access; a flue orifice in said chamber for removing fumes; a forced air channel surrounding the back, two sides, and bottom of said chamber; vertical vent means in the front wall of said side air channels adjacent the side of said opening and horizontal vent means in the front wall of said bottom air channel; means interior to said air channel for directing air over said back, two sides and bottom of said chamber; and means for forcibly introducing air into the back portions of said air channel 4o traverse said back, two sides, and bottom of said chamber to absorb heat and exit said front wall vent means creating an exiting forced air pattern adjadent the sides of said opening.

2. The heating unit according to claim 1 wherein said air introducing means draws air from in front of said unit exterior of the area defined by said vent means.

3. The heating unit according to claim 1 including a horizontal plate extending from said front wall separatubg said opening and horizontal vent means in said bottom air channel;

4. The heating unit according to claim 1 wherein said back air channel is interconnected to said two sides and bottom air channel and said bottom air channel is interconnected to said two side air channels. 5. The heating unit according to claim 1 including first means cooperating with said vertical vent means for directing the air exiting said vertical vent means to converge in front of said opening.

6. The heating unit according to claim 5 wherein said first means includes a vertical baffle plate interior said foreed air channel.

7. The heating unit according to claim 5 wherein said vertical vent means is offset from the exterior side wall of said forced air channel, said exterior side walls form an angle with said front wall of less than ninety degrees and said first means includes a pneumatic deflection plane formed in said air channel between the side wall and the adjacent portion of the front wall.

8. The heating unit according to claim 7 wherein said first means further includes a vertical L-shaped lip exterior to and having a portion extending across said vertical vent means to produce a pneumatic deflection plane exterior said vent.

9. The heating unit according to claim 5 including a second means in said vertical vent means for directing exiting air downward.

10. The heating unit according to claim 9 wherein said second means includes a mesh extending across said vertical vent means having a plurality of substantially horizontal portions inclined relative to the horizontal.

11. The heating unit according to claim 1 including inlet means in the rear portion of said forced air channel spaced from the bottom of said chamber receiving air from above and around the heating unit; and

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OMPI said air introducing means draws air into the inlet from the top and sides of the room in which the heating unit is placed, and exiting said vent means along the floor of said room to uniformly mix the air temperature in said room.

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12. The heating unit according to claim 11 wherein said vertical vent means include means for directing exiting air downward.

13. The heating unit according to claim 11 wherein said directing means include first baffle means in said back portion for radially directing the forced ai from said inlet means over said back wall of said chamber.

14. The heating unit according to claim 13 including second baffle means i said side portions -for radially directing the forced air to said vertical vent mean from said back wall portion over the side walls of said chamber.

15. The heating unit according to claim 13 including third baffle means i said bottom portion for directing air from said back portion over said bottom wal of said chamber to said side portions and said horizontal vent means.

16. The heating unit according to claim 15 wherein said third baffle mean include two sets of baffles on each side of the center of said bottom portion, th baffles in a set are substantially parallel to each other and the ends of said baffle adjacent said center are staggered relative to said center.

17. The heating unit according to claim 1 including a baffle depending fro the top of said fire box adjacent said flue port for retaining some of said gase adjacent said top and for directing some of said gases into a fire portion in sai chamber for ignition. - - handle and latch includes a vertical strip extending across said other door in the closed position to secure said other door.

24. The heating unit according to claim 1 including a draft opening to said chamber, a slide means movable relative to said opening to vary the exposed area of said draft opening, and said lockin means including a threaded member engaging said slide means and a surface of said chamber containing said opening and rotatable to lock said slide in a desired position.

25. The heating unit according to claim 24 wherein said surface is a door covering said access opening to said chamber.

26. The heating unit according to claim 1 including means connected to said air forcing means for monitoring the temperature in said forced air channel, activating said air forcing means at a first forced air temperature and deactivating said air forcing means at a second forced air temperature below said first forced air temperature to maintain the exterior portion of said chamber contiguous to said forced air channel at the lowest possible temperature while still heating the forced air.

27. The heating unit according to claim 26 wherein said first temperature is about 125 °F. and said second temperature is about 95° F.

28. A free-standing forced air heating unit comprising: a housing having a top, a bottom, a front, a back, and two side walls; a back and two interior walls adjacent to said back and two side walls of said housing for forming a substantially U-shaped forced air channel; an opening in said front wall for providing access to a chamber defined by the interior of said interior walls;

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OMPI -Ar-_* WIPO ,Λ -21-

18. The heating unit according to claim 17 including doors for closing said access opening, said doors being mounted to said heating unit spaced along their top edge from the top of said access opening to allow air to circulate into said chamber adjacent said top for aiding ignition of said gases adjacent said top.

19. The heating unit according to claim 1 including a hood mounted to said front wall and extending down toward said top edge of said access opening for directing gases exiting said access opening adjacent said top edge back into said chamber.

20. The heating unit according to claim 19 wherein said hood extends laterally beyond the width of said access opening and includes a side portion on each end extending between the main body portion of said hood and said front wall of said heating unit at a non-ninety degree angle to both.

21. In a heating unit according to claim 1 including a pair of doors covering said access opening, a handle on the exterior of one of said doors, a latch on the interior of said chamber connected to said handle through said door, said handle being rotatable down toward a vertical plane through the axis of rotation from a first position to a second position to latch said door by said latch engaging the interior wall and being rotatable away from said vertical plane to unlatch said door by disengaging said latch and said interior wall.^"

22. The heating unit according to claim 21 wherein said first position is above a horizontal plane through said axis of rotation and said second position is substantially in said horizontal plane.

23. The heating unit according to claim 21 wherein said door with said

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⁰ vent means in said front wall of said air channel adjacent the side edges of said opening; means mounted to said housing for drawing air from in front of said unit exterior of the area defined by said unit; and forcibly introducing air into the back portion of said channel through a port to traverse said air channel and to exit said vent means creating an exiting forced air pattern adjacent said side edges of said opening; first air directing means interior the back portion of said channel for directing said forced air to diverge radially from said port, to traverse a substantial portion of said back interior wall, and to enter the two side portions of said channel; and second air directing means interior each side portion of said channel for directing the forced air from said back portion to traverse a substantial portion of said side interior walls and to converge on said vent means.

29. An heating unit comprising: a chamber for holding a source of heat having a top, a bottom, a front, a back, and two side walls; a back, two side, and a bottom wall exterior and adjacent respective walls of said chamber forming forced air channels therebetween; vent means in a front wall of said sides and bottom air channels; means for forcibly introducin T iiFThto ^"the back channel through a port to traverse said back, two side, and bottom of said chamber to absorb heat and exit said vent means; first directing means interior the back air channel for directing said forced air to diverge from said port, to traverse a substantial portion of the back wall of said chamber to absorb heat and exit said vent means; second directing means interior the bottom air channel for directing the

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OMPI r W1PO Λ forced air from the back air channel to traverse a substantial portion of the bottom wall of said chamber, to enter the side air channels and to exit the bottom air channel's vent means; and third air directing means interior each of the side air channels for directing the forced air from the back and bottom air channels to traverse a substantial portion of the side walls and to converge on the side air channels' vent means.

30. The heating unit of claim 29 wherein said chamber includes an opening in said front wall for providing access, and said vent means are adjacent the sides of said opening to surround substantial portions of said sides and bottom of said access opening with exiting forced air.

31. The heating unit of' claim 29 wherein the side walls of said forced air chamber form an angle with said front wall of said side air channel less than ninety degrees and including a lip encompassing said side air channels vent means extending substantially perpendicular from a front wall of said side air channels and extends across said side air channels' vent means.