Abstract:
A filter frame is removably attachable to a box fan. The filter frame is adapted for receiving a standard HVAC-style filter for removing contaminants from air flow induced by the fan. In this manner, a cost-effective means for filtering a flow of air is provided for residential and commercial settings. The filter frame is adaptable to a variety of standard box fan types of different styles and dimensions. The frame is configured to accommodate standard filters, such as those readily available from retail hardware stores and home centers.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. application Ser. No. 14/448,350, filed on Jul. 31, 2014 which is a continuation application of U.S. application Ser. No. 14/062,271, filed on Oct. 24, 2013, which is a continuation application of U.S. application Ser. No. 13/713,756, filed Dec. 13, 2012, now U.S. Pat. No. 8,591,619, which is a continuation application of U.S. application Ser. No. 13/403,362, filed on Feb. 23, 2012, now U.S. Pat. No. 8,349,047, which is a continuation application of U.S. application Ser. No. 13/022,921, filed Feb. 8, 2011, now U.S. Pat. No. 8,137,426, which is a continuation of U.S. application Ser. No. 12/691,219, filed on Jan. 21, 2010, now U.S. Pat. No. 7,905,938, which is a continuation application of U.S. application Ser. No. 11/344,749, filed Feb. 1, 2006, now U.S. Pat. No. 7,670,401, which claims the benefit of U.S. Provisional Application Ser. No. 60/648,892, filed Feb. 1, 2005, U.S. Provisional Application Ser. No. 60/661,529 filed Mar. 14, 2005, and U.S. Provisional Application Ser. No. 60/737,190, filed Nov. 16, 2005, the contents of each of which are incorporated herein by reference, in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Portable fans, such as box fans, are popular as a cost-efficient means for cooling or ventilating interior areas of commercial and residential buildings. Box fans are inexpensive, light, and portable, and can be easily repositioned to provide a desired interior air flow. 
         [0003]    Filters have been applied to box fans as a means for removing air-borne contaminants from the air flow. A number of mounting configurations have been devised that secure a filter to a box fan. U.S. Design Pat. No. DES 377,390 discloses a filter mount that is incorporated within the body of a box fan. This configuration requires a specialized fan chassis, and therefore is not applicable to general-purpose box fans. U.S. Pat. No. 4,781,526 discloses a filter mount that is affixed to an exterior portion of a fan body. In this configuration, the filter bracket is permanently affixed to holes formed in the fan body using specialized mounting hardware, such as machine screws. U.S. Pat. No. 6,527,838 discloses a filter mount including a plurality of brackets that adhere to a side surface of the fan. The brackets are permanently affixed to the fan, and take the form of specialized hardware, which, when mounted to a particular fan body, cannot be re-used on another fan. In alternative embodiments disclosed in the U.S. Pat. No. 6,527,838 patent, a filter bracket is applied to a fan body using hook and loop fasteners or screws about a periphery of the body of the fan. Again, such specialized attachment hardware is semi-permanent, can disfigure the fan body, and cannot be re-used on another fan. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is directed to a filter mount for a box fan. A filter mount in the form of a frame is removably mountable to a fan chassis and does not cause any permanent disfigurement to the fan body. The filter frame is adapted and shaped to receive a standard air filter, such as the type of filter commonly used in residential heating systems. The filter and frame are preferably sized to closely match, and cover, a standard-sized fan grill at the input or output face of the fan, so that a substantial amount of air flow passes through the filter. 
         [0005]    The filter frame is preferably sized to have a narrow profile so as not to inhibit the air flow induced by the fan. In one embodiment, straps are provided to secure the frame to the fan body, such that the frame is readily removable. In one embodiment, the straps comprise elastic bands. Tension in the elastic bands, when mounted, secures the filter frame to the fan chassis. The elastic bands are optionally adjustable in length so that the filter frame is compatible with a variety of fan chassis types and a variety of fan chassis thicknesses. 
         [0006]    In another embodiment, the frame includes features that attach to a grill of a fan, for example, features that mate with one or more grill apertures. The frame can include, for example rigid pegs or hooks that are inserted in one or more grill apertures at one of a top and bottom of the fan grill, and spring-loaded hooks that are inserted in one or more grill apertures at the other of the top and bottom of the fan grill to secure the frame in place against the fan grill. 
         [0007]    In another embodiment, a filter frame can be integrated directly into the grill of the fan. In this embodiment, the fan grill can be formed in a molding process to include integral filter guides at left side, right side, and bottom side portions of the fan grill. In this manner, the fan grill includes an integral filter frame that can accept standard-sized filters. 
         [0008]    In this manner, a cost-effective means for filtering a flow of air is provided for residential and commercial settings. The filter frame is adaptable to a variety of standard box fan types of different styles and dimensions. The frame is configured to accommodate standard filters, such as those readily available from retail hardware stores and home centers. 
         [0009]    In one embodiment, the filter frame includes one or more elastic bands, or bungy cords. Each elastic band is attached at a first end to one of the side members of the filter frame. A second end of each elastic band includes a hook that is adapted to attach to one of the front and rear grills of the fan, or other feature of the fan. The frame is mounted to one face of the fan body, and the elastic band or bands stretch about the sides of the fan to the other face of the fan body. The hooks operate in conjunction with the tension in the stretched band or bands to secure the filter frame to the fan body. 
         [0010]    In one embodiment, a single pair of bands is employed, one band interfacing with each respective left and right side member of the frame at or near a central position of the side members. In some configurations, a single pair of bands is sufficient for securing the frame to the fan body. In another embodiment, where additional securing force is required, multiple pairs of bands are employed, each band of each pair interfacing with a left or right side member at top and bottom regions of the side members. 
         [0011]    The elastic bands may be permanently attached to the frame, for example, by rivets or screws, or by tying the bands to the frame. Alternatively, the elastic bands are removable from the frame, for example, by hooks, buttons, loops, or other attachment mechanisms. One end, or both ends, of each elastic band can be removably or permanently attached to the frame. 
         [0012]    In an embodiment where both ends of each elastic band attach to the frame, one or more of the bands loop around the fan body, for example over the top, bottom, left and/or right sides of the fan body, to secure the frame to the fan body. As mentioned above, the ends of each elastic band may be permanently or removably attached to the frame. 
         [0013]    In an embodiment where a first end of each elastic band is attached to the frame, the second end includes a hook for attaching the elastic band to a feature of the fan chassis, for example, a fan grill, handle, or other feature. In another embodiment, elastic bands from left and right sides of the frame each include hooks, or other clasping features, such that the second ends of paired elastic bands can be coupled to each other to form one large band that extends about the fan chassis. In another embodiment, the frame includes pegs that extend from the frame and extend between adjacent cross members of the rear or front grill of the fan, such that the pegs prevent the frame from shifting or sliding relative to the cross members. 
         [0014]    In another embodiment, the filter frame includes mounting knobs at spaced-apart coupling locations, and the elastic bands each include an array of holes at first ends of the bands. The holes of the elastic bands mate with the coupling knobs as a convenient mechanism for removably attaching the elastic bands to the filter frame. The second ends of the elastic bands may include hooks, as described above, for attaching to a fan chassis feature. Alternatively, the elastic bands include an array of holes at both ends, and the bands stretch about the body of the chassis, and couple to both sides of the frame. The mounting knobs secure the bands, and retain the elastic bands in a tensioned state, securing the filter frame to the fan. The array of holes are distributed along the length of the end of each band to allow for adjustment in the length of the elastic band. In this manner, the filter frame is adapted to accommodate fan bodies of different thicknesses. 
         [0015]    In another embodiment, the filter frame is secured to the fan chassis by elongated bolts that extend through the body of the fan. Holes are included in the frame to receive the bolts. The holes are preferably elongated to allow for play in positioning the frame relative to the fan body, so that the frame is compatible with different fan grill configurations. The elongated bolts are secured to the filter frame and fan with washers and wing nuts, which, when tensioned, retain the filter frame against the body of the fan. The bolts are configured so as to avoid interference with fan operation. 
         [0016]    In another embodiment, the filter frame is secured to the fan chassis using fasteners that are bolted to the frame. In one embodiment, the fastener is inserted into the fan grill in a horizontal position between cross members of the rear or front grill of the fan, and is then rotated to a vertical position and tightened in place to affix the filter frame to the fan. The fastener is sized to accommodate a range of fan grill configurations. 
         [0017]    In an alternative embodiment, the frame is attached to the rear or front grill of a fan with standard cable ties. 
         [0018]    In another embodiment, the filter frame is unitary and formed in a molding process, for example in a straight-pull injection molding process. 
         [0019]    In another embodiment, the filter frame is adapted to receive multiple filters. 
         [0020]    In another embodiment, the filter frame is unitary and formed in a molding process and includes spring-loaded hooks for securing the filter frame to the grill of the fan. 
         [0021]    In another embodiment, the filter frame is integral with the front or rear grill of the fan body. The filter frame is molded on an outer portion of the front or rear grill, the filter frame and the front or rear grill being unitary. 
         [0022]    In one aspect, the present invention is directed to a removable filter frame for a fan. A frame body includes opposed first and second side channels. Each of the first and second side channels has a longitudinal axis and the first and second side channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. The removable filter frame further comprises a coupler that extends from the frame body in a direction transverse to the longitudinal axes of the first and second side channels. The coupler is constructed and arranged to couple the frame body to a grill of a fan. 
         [0023]    In one embodiment, the frame body is unitary. Further, in another embodiment, the frame body is formed in a straight-pull injection molding process. 
         [0024]    In another embodiment, the first and second side channels of the frame body are formed as separate units that are mounted together. 
         [0025]    In another embodiment, the frame body further includes at least one cross member between the first and second side channels that provides for lateral rigidity to the frame body. 
         [0026]    In another embodiment the first and second side channels each comprise a side surface of the frame body and tabs that extend from the frame body in a horizontal direction to define the first and second side channels. 
         [0027]    In another embodiment, the stop is positioned at a bottom of at least one of the first and second side channels. In another embodiment, the stop comprises a portion of the frame body that extends in a horizontal direction between the longitudinal axes of the first and second side channels. Further, in another embodiment, the stop comprises a horizontal channel extending in the horizontal direction between bottom portions of the first and second side channels. 
         [0028]    In another embodiment, the coupler comprises at least one tab that extends from the frame body and is constructed and arranged to couple the frame body to a grate of a grill of a fan. 
         [0029]    In another embodiment, the coupler comprises at least one hook that extends from the frame body and is constructed and arranged to couple the frame body to a grate of a grill of a fan. In another embodiment, the at least one hook is spring-loaded. 
         [0030]    In another embodiment, the coupler comprises one of multiple fasteners, multiple elongated bolts, and multiple cable ties that extend from the frame body and are constructed and arranged to couple the frame body to a grate of a grill of a fan. 
         [0031]    In another embodiment, the removable filter frame further comprises elastic bands that are coupled to the frame body and are constructed and arranged to couple about a chassis of a fan. 
         [0032]    In another embodiment, the removable filter frame further comprises a foam pad coupled between the frame body and a grill of a fan. 
         [0033]    In another embodiment, the first side channel and the second side channel are constructed to have a depth such that multiple filters can be inserted in the frame body. 
         [0034]    In another aspect, the present invention is directed to a removable filter frame for a fan. A frame body includes opposed first and second side channels. The first and second side channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. At least one elastic band is coupled to the frame body, the at least one elastic band is constructed and arranged to extend about a portion of a fan chassis so that when installed, tension in the at least one elastic band operates to secure the frame body to a fan. 
         [0035]    In one embodiment, the frame body is unitary. 
         [0036]    In another embodiment, the frame body is formed in a straight-pull injection molding process. 
         [0037]    In another embodiment the first and second side channels of the frame body are formed as separate units that are mounted together. 
         [0038]    In another embodiment, the frame body further includes at least one cross member between the first and second side channels that provides lateral rigidity to the frame body. 
         [0039]    In another embodiment, the first and second side channels each comprise a side surface of the frame body and tabs that extend from the frame body in a horizontal direction to define the first and second side channels. 
         [0040]    In another embodiment, the stop is positioned at a bottom of at least one of the first and second side channels. In another embodiment, the stop further comprises a portion of the frame body that extends in a horizontal direction between the first and second side channels. In another embodiment, the stop comprises a horizontal channel extending in the horizontal direction between bottom portions of the first and second side channels. 
         [0041]    In another embodiment, the at least one elastic band comprises a plurality of elastic bands, each coupled at both ends to the frame body. 
         [0042]    In another embodiment, the at least one elastic band comprises a plurality of elastic bands, each coupled at one end to the frame body. 
         [0043]    In another embodiment, each of the elastic bands of the plurality of elastic bands further comprises a hook at at least one end. The hook is constructed and arranged to couple the frame body to a grate of a grill of a fan. 
         [0044]    In another embodiment, each of the elastic bands of the plurality of elastic bands comprises a hook at a first end and a plurality of holes at a second end and the frame body further comprises knobs. The plurality of holes at the second end of each of the plurality of elastic bands is adapted to mate with one of the knobs to define a length of each of the elastic bands between the knob of the frame body and the hook. 
         [0045]    In another embodiment, the at least one elastic band is removably coupled at at least one end to the frame body. 
         [0046]    In another embodiment, the at least one elastic band is fixed at at least one end to the frame body. 
         [0047]    In another embodiment, the first and second side channels are constructed to have a depth such that multiple filters inserted in the frame body. 
         [0048]    In another embodiment, the removable filter frame further comprises a coupler extending from the frame body in a direction transverse to longitudinal axes of the first and second side channels. The coupler is constructed and arranged to couple the frame body to a grill of a fan. 
         [0049]    In another embodiment, the coupler comprises at least one tab that extends from the frame body and is constructed and arranged to couple the frame body to a grate of a grill of a fan. 
         [0050]    In another embodiment, the coupler comprises at least one hook that extends from the frame body and is constructed and arranged to couple the frame body to a grate of a grill of a fan. In another embodiment, the at least one hook is spring-loaded. 
         [0051]    In another embodiment, the coupler comprises one of multiple fasteners, multiple elongated bolts, and multiple cable ties that extend from the frame body and are constructed and arranged to couple the frame body to a grate of a grill of a fan. 
         [0052]    In another aspect, the present invention is directed to grill for a fan. A latticed grate includes cross members and openings and has an inner surface and an outer surface. Retaining members extend from the outer surface of the grate in a direction transverse to the outer surface at first and second outer regions of the grill to define opposed first and second side channels. The first and second side channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. 
         [0053]    In one embodiment, the grate and the retaining members are formed in a molding process so that they are unitary. In another embodiment, the grate and the retaining members are formed in a straight-pull injection molding process. 
         [0054]    In another embodiment, the retaining members are L-shaped. A first portion of each retaining member extends from the outer surface in a direction transverse to the outer surface and a second portion of each retaining member extends from the first portion of the retaining member in a direction substantially parallel to the outer surface and toward a middle region of the grate. 
         [0055]    In another embodiment, the stop is L-shaped. A first portion of the stop extends from the outer surface in a direction transverse to the outer surface and a second portion of the stop extends from the first portion of the stop in a direction substantially parallel to the outer surface and toward a middle region of the grate. 
         [0056]    In another embodiment, the stop is integrated into the retaining members at a low end of the slot. 
         [0057]    In another embodiment, each of the first and second side channels includes multiple retaining members. 
         [0058]    In another embodiment, each of the first and second side channels includes a single retaining member. 
         [0059]    In another embodiment, the stop comprises multiple stops. 
         [0060]    In another aspect, the present invention is directed to a fan. The fan includes fan blades and a motor that operates the fan blades. A fan chassis surrounds the motor and fan blades. Front and rear grills shield the fan blades and allow for air movement through the fan. Each of the front and rear grills includes a latticed grate having cross members and openings and has an inner surface and an outer surface. Retaining members extend from the outer surface of the grate of at least one of the front and rear grills in a direction transverse to the outer surface at first and second outer regions to define opposed first and second side channels. The first and second side channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. 
         [0061]    In one embodiment the grate and the retaining members are formed in a molding process so that they are unitary. 
         [0062]    In another aspect, the present invention is directed to a method of mounting a filter to a fan. The method includes coupling a frame body having opposed first and second side channels, each of the first and second side channels having a longitudinal axis, to a grill of a fan by couplers extending from the frame body in a direction transverse to the longitudinal axes of the first and second side channels. The couplers engage a grate of the grill through an opening in the grate. The first and second side channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. An air filter is inserted into an upper end of the slot. 
         [0063]    In one embodiment, coupling the frame body to the grill of the fan further comprises coupling the frame body to a grate of the grill of the fan using at least one tab extending from the frame body. 
         [0064]    In another embodiment, coupling the frame body to the grill of the fan further comprises coupling the frame body to a grate of the grill of the fan using at least one hook extending from the frame body. In another embodiment, the at least one hook is spring-loaded. 
         [0065]    In another aspect, the present invention is directed to a method of mounting a filter to a fan. The method comprises coupling a frame body having opposed first and second side channels to a grill of a fan by at least one elastic band extending about a portion of a fan chassis so that when installed, tension in the at least one elastic band operates to secure the frame body to a fan. The first and second channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. An air filter is inserted into an upper end of the slot. 
         [0066]    In another aspect, the present invention is directed to a method that comprises forming a grill for a fan including a latticed grate including cross members and openings and having an inner surface and an outer surface. The method further comprises forming retaining members that extend from the outer surface of the grate in a direction transverse to the outer surface at first and second outer regions of the grill to define opposed first and second side channels. The first and second side channels define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop for restricting further movement of an inserted air filter. The method further comprises mounting the grill to a fan chassis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0067]    The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
           [0068]      FIGS. 1A and 1B  are perspective views of an embodiment of the present invention.  FIG. 1A  is a perspective view of a filter frame including elastic bands and  FIG. 1B  is a perspective view of the filter frame of  FIG. 1A  attached to a box fan, in accordance with the present invention. 
           [0069]      FIGS. 2A-2D  are perspective views of another embodiment of the present invention.  FIG. 2A  is a perspective view of an elastic band including an array of holes.  FIG. 2B  is a perspective view of the elastic bands of  FIG. 2A  attached to a box fan.  FIG. 2C  is a perspective view of a filter frame including mounting knobs.  FIG. 2D  is a perspective view of the filter frame of  FIG. 2C  attached to the box fan of  FIG. 2B  by the elastic bands of  FIG. 2A , in accordance with the present invention. 
           [0070]      FIGS. 3A and 3B  are perspective views of another embodiment of the present invention.  FIG. 3A  is a perspective view of a filter frame attachable to a box fan using elastic bands that are attached to the frame at both ends of the bands.  FIG. 3B  is a perspective view of the filter frame of  FIG. 3A  attached to a grill of a box fan, in accordance with the present invention. 
           [0071]      FIG. 4  is a perspective view of another embodiment of the present invention including a filter frame attachable to a grill of a box fan using elongated bolts, washers and wing nuts. 
           [0072]      FIG. 5  is a perspective view of another embodiment of the present invention including a filter frame attachable to a grill of a box fan using a threaded fastener and bolt. 
           [0073]      FIGS. 6A and 6B  are perspective views of another embodiment of the present invention.  FIG. 6A  is a perspective view of a standard cable tie and  FIG. 6B  is a perspective view of a filter frame attachable to a grill of a box fan using the standard cable tie of  FIG. 6A , in accordance with the present invention. 
           [0074]      FIG. 7  is a perspective view of another embodiment of the present invention, in which the filter frame includes first and second side members and no base member, and in which a foam pad is applied between the frame and the fan body, in accordance with the present invention. 
           [0075]      FIG. 8  is a perspective view of another embodiment of the present invention, in which the filter frame includes a widened channel that is adapted to receive both a universal filter and a HEPA-standard filter, in accordance with the present invention. 
           [0076]      FIG. 9  is a close-up perspective view of a side member of the filter frame of  FIGS. 7 and 8 , including a channel stop at an end of the channel, in accordance with the present invention. 
           [0077]      FIGS. 10A and 10B  are illustrations of another embodiment of the present invention.  FIG. 10A  is a front view of another embodiment of a filter frame formed in a mold process.  FIG. 10B  is a close-up perspective view of a side edge of the filter frame of  FIG. 10A . 
           [0078]      FIGS. 11A ,  11 B,  11 C and  11 D are perspective views of another embodiment of the present invention.  FIG. 11A  is a perspective view of another embodiment of the molded filter frame of  FIGS. 10A and 10B  including spring-loaded hooks for latching the filter frame to the grill of the fan.  FIG. 11B  is a close-up perspective view of a top corner of a rear face of the filter frame of  FIG. 11A  including the spring-loaded hooks.  FIG. 11C  is a close-up perspective view of a corner of a front face of the filter frame of  FIG. 11A .  FIG. 11D  is a perspective view of the filter frame of  FIG. 11A  mounted to a fan body. 
           [0079]      FIGS. 12A-12C  are perspective views of another embodiment of the present invention.  FIG. 12A  is a perspective view of another embodiment of the molded filter frame of  FIGS. 10A and 10B  including spring-loaded hooks for latching the filter frame to the grill of the fan.  FIG. 12B  is a close-up perspective view of a bottom corner of a rear face of the filter frame of FIG.  12 A including spring-loaded hooks.  FIG. 12C  is a close-up perspective view of a top corner of a rear face of the filter frame of  FIG. 12A . 
           [0080]      FIGS. 13A-13E  are perspective views of another embodiment of the present invention.  FIG. 13A  is an embodiment of the filter frame integral with a fan grill attached to the fan body.  FIG. 13B  is a close-up perspective view of a side edge of the filter frame and the fan grill of  FIG. 13A .  FIG. 13C  is an exploded perspective view of an embodiment of a box fan and fan grill with an integral filter frame.  FIGS. 13D and 13E  are assembled views of alternative embodiments of the fan grill with an integrated filter frame. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0081]      FIG. 1A  is a perspective view of a filter frame  32  adapted to be secured to a body of a portable fan, such as a standard box fan, using elastic bands  33 . A filter frame  32  is configured to include frame channels in a U-shaped arrangement having first and second side members  42  and a base member  44 . Cross-members  37  are coupled between opposite corners of the frame to provide lateral rigidity. The first and second side members  42  include longitudinal channels  46  that are spaced apart and opposed, and that provide a slot or seat for receiving side edges of an inserted filter. The base member  44  extends between the first and second side members  42  and includes a similar longitudinal channel  47  that is aligned with the longitudinal channels  46  of the side members  42  for receiving a bottom edge of an inserted filter. Top portions of the side member frame channels  46  are open to provide an insertion and removal location for the filter. The side members  42 , base member  44 , and cross members  37  of the filter frame  32  comprise extruded aluminum, plastic, graphite, or other suitable light-weight and durable material that is molded or otherwise machined or formed. The members may be riveted, bolted, welded, or otherwise coupled together, or may be molded and formed as a complete unit. 
         [0082]    Elastic bands  33  are permanently attached, at first ends, to a top right corner, bottom right corner, top left corner and bottom left corner of the filter frame  32 . The elastic bands  33  are, for example, riveted, bolted, tied, or otherwise attached to the frame  32 . The elastic bands  33  further include hooks  34 , or other clasping mechanisms, at a second end. The elastic bands  33  comprise, for example, bungy cords, elastic ribbons, or straps. In alternative embodiments, the hooks  34  on the elastic bands  33  are tied, coupled to, or integral with, the elastic bands  33  at their second ends. The hooks  34  are preferably coated with a soft plastic or rubber material to avoid scratching the fan chassis. 
         [0083]    The frame  32  is preferably sized to closely match, and cover, a standard-sized fan grill at an input or output face of the fan, so that a substantial amount of air flow induced by the fan passes through the inserted filter. The side members  42 , base member  44  and cross members  37  of the filter frame are preferably sized to have a narrow profile so as to reduce the restriction of air flow. In one embodiment, the frame channels  46  are spaced apart a suitable distance, and foamed of a depth, so as to accommodate a general purpose forced-air filter, for example ¾″ by 20″ by 20″ in size. The 20″ by 20″ filter profile matches well with a variety of box fan sizes. Therefore, the depth of the channel  46  in this example is made to be slightly larger than ¾″ and the side members  42  are spaced apart slightly more than 20″ in order to accommodate an inserted filter. Other filter sizes and other channel depths can also be applied to accommodate fans and filters of varying dimensions, and are equally applicable to the present invention. 
         [0084]      FIG. 1B  is a perspective view of the filter frame  32  of  FIG. 1A  attached to a box fan  31 . The frame  32  is positioned at a first face  52  of the box fan  31  and the elastic bands  33  are pulled about the sides of the fan chassis to a second face  54  of the fan  31 . The hooks  34  are clasped to an existing feature of the box fan  31 , for example a grate of a grill  71  on the second face  54  of the fan. Tension in the stretched elastic bands  33  retains the filter frame  32  against the fan body  31 . Although the above described embodiment illustrates multiple bands  33  with hooks  34  at each of the first and second side members  42 , each side member  42  can optionally include a single elastic band/hook, depending on the application. The elastic band configuration is equally applicable to any of the filter frame embodiments described herein. 
         [0085]      FIGS. 2A-D  are perspective views of another embodiment of the present invention.  FIG. 2A  is a perspective view of an elastic band  38  having a hook  34  at a proximal end and an array of holes  50  at a distal end. In one embodiment, the holes  50  are spaced ¾″ apart and are distributed longitudinally along the end of the elastic band  38 . 
         [0086]      FIG. 2B  is a perspective view of the elastic bands  38  of  FIG. 2A  hooked onto a grate of a grill  71  at a second face  54  of the box fan  31  at top right, bottom right, top left, and bottom left positions by the hooks  34 . 
         [0087]      FIG. 2C  is a perspective view of a filter frame  32  of a construction generally similar to that described above in  FIG. 1A . In this embodiment, however, the elastic bands are not permanently attached. Instead, the filter frame  32  includes mounting knobs  41  that extend from the body of the frame  32  at top right, bottom right, top left and bottom left corners of the frame. The mounting knobs  41  have relatively narrow necks with relatively wide heads, such that when the holes  50  at the distal ends of the elastic bands  38 , held in place at their proximal ends by the hooks  34 , are pulled over the knobs  41 , the elastic bands  38  are seated in position by the heads of the knobs  41 . 
         [0088]      FIG. 2D  is a perspective view of the filter frame of  FIG. 2C  attached to the box fan  31  of  FIG. 2B  by the elastic bands  38  of  FIG. 2A . The holes  50  of the elastic bands  38  are pulled over the mounting knobs  41  of filter frame  32  to secure the four corners of the filter frame  32  to the box fan  31 . Tension in the stretched elastic bands  38  retains the filter frame  32  against the body of the fan  31 . Different holes  50  of the elastic bands  38  can be used to accommodate fan bodies  31  of different thicknesses, and to accommodate a range of different positions for hooking the hooks  34  on the grill, or other feature, of the fan. The mounting knob/elastic band configuration can be applied to any of the frame embodiments described herein. 
         [0089]    In another embodiment, each of the upper and lower pairs of elastic bands  33 ,  38  of the  FIG. 1  and  FIG. 2  embodiments described above can be dimensioned in length so that their hooks  34 , or other clasping features, can be coupled to each other to form one large band that extends about the fan chassis to secure the filter frame  32  in place. 
         [0090]      FIGS. 3A and 3B  are perspective views of another embodiment of the present invention.  FIG. 3A  is a perspective view of a filter frame  32  attachable to a box fan using elastic bands. In this embodiment, the elastic bands  25   a ,  25   b  are permanently coupled to the opposed first and second side members  42  of the filter frame  32 . A first elastic band  25   a  extends across the filter frame  32  from the top right corner to the top left corner, and a second elastic band  25   b  extends from the bottom right corner to the bottom left corner of the filter frame  32 . When mounting the frame  32  to a box fan  31 , as shown in  FIG. 3B , the first elastic band  25   a  is pulled over the top of the box fan  31 , and the second elastic band  25   b  is pulled over the bottom of the box fan  31 . Alternatively, the first and second elastic bands  25   a ,  25   b  can both be pulled over the top or the bottom of the box fan  31  and positioned into place. The tension in the elastic bands  25   a ,  25   b  retains the filter frame  32  against the box fan  31 . In alternative embodiments, one end, or both ends, of the elastic bands  25   a ,  25   b  are removable from the filter frame  32 , for example using the holes and knobs combination described above with reference to  FIGS. 2A-2D . This elastic band configuration is equally applicable to any of the filter frame embodiments described herein. 
         [0091]      FIG. 4  is a perspective view of another embodiment of the present invention including a filter frame attachable to a grill of a box fan  31  using elongated bolts  53 , washers  65  and wing nuts  64 . In this embodiment, the filter frame  32  is secured to the fan chassis  31  by elongated bolts  53  that extend through the fan  31 . For example, the bolts  53  can be configured to be of a length so as to extend through grate openings that exist in both the front and rear grills  71  of the fan  31 . Holes  62  are included in the frame  32  at the cross members  37  or side members  42  to receive the bolts  53 . The holes  62  are preferably elongated to allow for play in positioning the frame  32  relative to the fan body  31 , so that the frame  32  is compatible with different fan grill configurations. The elongated bolts  53  are secured to the filter frame  32  and fan  31  with washers  65  and wing nuts  64 , which, when tensioned, retain the filter frame  32  against the body of the fan  31 . The holes  62  and bolts  53  are configured to align with the four corners of the fan grill, so as to avoid interference with fan operation. The bolts  53  are preferably of a length so as to accommodate fan bodies of different depths. Tightening the wing nuts  64  creates a tension in the bolts that retains the filter frame  32  against the fan body  31 . The wing nuts  64  and bolts  53  are readily mountable by an individual without the need for tools. The elongated bolt and wing nut mounting configuration can be applied to any of the filter frame embodiments described herein. 
         [0092]      FIG. 5  is a perspective view of another embodiment of the present invention including a filter frame  32  attachable to a grill of a box fan  31  using fasteners  18 . The fasteners  18  are bolted to the frame  32 , for example at cross-members  37  or side members  42 . Holes  67  are included in the frame  32  to receive the bolts  66 . The holes  67  are preferably elongated to allow for play in positioning the frame  32  relative to the fan body  31 , so that the frame  32  is compatible with different fan grill configurations. A fastener  18  is inserted into a fan grill  71  in a horizontal position between cross members of the rear or front fan grill  71  of the fan, and is then rotated to a vertical position and tightened in place with bolt  66  to affix the filter frame  32  to the fan  31 . The fastener  18  is sized to accommodate a range of fan grill configurations. The fastener  18  may include a threaded hole  68  to receive the bolt  66 , or, optionally washers and nuts may be employed. Tightening the bolt  66  relative to the fastener  68  provides tension which holds the frame  32  against the box fan  31 . The fastener configuration described in  FIG. 5  is equally applicable to any of the filter frame embodiments described herein. 
         [0093]      FIGS. 6A and 6B  are perspective views of another embodiment of the present invention. In this embodiment, a plurality of standard cable ties  69  as shown in  FIG. 6A  are used to mount the filter frame  32  to the grill of the box fan  31  as shown in  FIG. 6B . Holes  67 , for example elongated holes, are formed in the cross members  37  or side members  42  of the frame  32 , and standard cable ties  69  are wrapped around the holes  67  and a grate of the fan grill  71 , and tightened, to secure the filter frame  32  against the fan grill  71 . The excess portion of the cable tie  20  is preferably cut off to avoid vibration during fan operation, and to avoid interference with an inserted filter. The cable ties  69  are tightened so as to create sufficient tension to secure the filter frame  32  to the box fan  31 . The cable tie configuration described in  FIG. 6  is equally applicable to any of the filter frame embodiments described herein. 
         [0094]      FIG. 7  is a perspective view of another embodiment of the present invention. In this embodiment, the filter frame  32  includes first and second side members  42 A,  42 B and no base member. In this embodiment, rather than including a base member  44  as shown in the above embodiments of  FIGS. 1-6 , the side members  42 A,  42 B of the present embodiment each include a channel stop  106  at or near a distal end of the channel  46 , in order to limit or stop the insertion of a filter  100 , as shown in  FIG. 9 . The channel stop  106  can take the form of a solid face, a mesh surface, a peg, a dimple, or any suitable means for restricting downward movement of the filter  100  in the channel  46 . The channel stop structure can be applied to any of the filter frame embodiments described herein. 
         [0095]    Further, in the embodiment of  FIG. 7 , a single pair of elastic bands  33  and hooks  34  is included for mounting the filter frame  32  to the fan body. A single pair of elastic bands  33  can be equally as effective as a double pair as shown above in  FIGS. 1 ,  2  and  3  for securing the frame  32  to the fan body  31 , depending on the application. 
         [0096]    In addition, the embodiment of  FIG. 7  includes an optional foam pad  108  or gasket that is applied between the filter frame  32  and the fan body  31 . The foam pad  108  includes an opening  109  that allows free passage of air, the opening  109  being about as large as the cross-section of the volume of air that the fan is designed to push, so as not to restrict air flow. The foam pad  108  prevents air from entering the fan at a gap that may be present between the filter frame  32  and the surface of the fan body  31 . In this manner, the foam pad  108  causes more of the air that is pushed by the fan to pass through the filter  100 , thereby improving the air cleaning efficiency of the system. Further, if the foam pad  108  is cut to closely match the diameter of the fan blades, back draft in the corners of the box fan can be prevented. By preventing the back draft in the box fan, an air flow can be created that flows in a single direction, thus making the fan more efficient in configurations in which negative air pressure is created. The foam pad configuration can be applied to any of the filter frame embodiments described herein. 
         [0097]      FIG. 8  is a perspective view of another embodiment of the present invention. In this embodiment, the filter frame  32  includes a widened channel  46 . The channel  46  is widened so as to accommodate both a universal pre-filter  100  and a High Efficiency Particulate Air (HEPA) type filter  102 , in accordance with the present invention. The widened channel  46 , in one embodiment, is a single channel that is of a width so as to accommodate both the universal pre-filter  100  and the HEPA filter adjacent each other. In another embodiment, the channel  46  may comprise a double channel that includes a central rail for partitioning first and second slots of the channel. In this manner, either, or both, filters  100 ,  102  can be properly seated in designated slots of the channel  46 . This widened channel configuration can be applied to any of the filter frame embodiments described herein. 
         [0098]    Further, the embodiment of  FIG. 8  includes pegs or bumps  104  that extend in a direction transverse to the longitudinal direction of the filter channels from a face of each side member  42 A,  42 B or optionally from the cross members  37  or other portion of the frame  32 . The pegs  104  are adapted to rest in an opening between adjacent grates of the fan grill  71 . The pegs  104  prevent the frame  32  from shifting or sliding in a downward direction when the frame  32  is mounted to the fan and prevent movement of the frame  32  relative to the fan as a result of vibration. In one embodiment, the pegs  104  are approximately ¼″ in length. The peg configuration is equally applicable to any of the filter frame embodiments described herein. 
         [0099]      FIGS. 10A and 10B  are illustrations of another embodiment of the present invention.  FIG. 10A  is a front view of another embodiment of a filter frame  74  that is suitable for formation in a mold process. This embodiment of the filter frame  74  includes first and second spaced-apart and opposing side channels  46  that are defined by a plurality of side channel tabs  76 . The channels  46  provide a guide for receiving opposite edges of an inserted filter. The frame  74  further includes cross-members  37  that are coupled between opposite corners of the frame to provide lateral rigidity. The lowest side tabs  76  of the channels  46  are provided with bottom surfaces  78  that operate as a stop to limit the vertical position of the inserted filter. A top portion  89  of the frame  74  is open to provide an insertion and removal location for the filter. The left and right edges of the frame include mounts  80 , each comprising an opening for attaching elastic bands, bolts and nuts, hooks, or other fastening means to secure the filter frame  74  to the fan body, for example in the manner of the other embodiments described herein. 
         [0100]      FIG. 10B  is a close-up perspective view of a side edge of the filter frame  74  of  FIG. 10A . In this view it can be seen that a void  82  is provided in the channel  46  under each respective side tab  76 . In this manner, the filter frame of the present embodiment can be formed in a straight-pull injection molding process, such that there are no secondary movements required inside the mold during the molding process. An extension formed in the lower mold passes through a region where the voids  82  are to be formed. When the upper and lower molds are in position, material is injected, and the extension formed in the lower mold defines a lower part of the side tabs  76 . When the mold is retracted, the extensions pass through the voids that are formed below the tabs, so as to form the frame in a straight-pull injection molding process. In this embodiment, the side edges, side tabs  76 , bottom surfaces  78 , notches  80 , and cross members  37  of the filter frame  74  comprise aluminum, plastic, composite, graphite, or other suitable light-weight and durable material that can be formed in a molding process. The molded filter frame of  FIG. 10A  formed in the straight-pull injection molding process is equally applicable to any of the filter frame embodiments described herein. 
         [0101]      FIGS. 11A ,  11 B,  11 C and  11 D are perspective views of another embodiment of the present invention.  FIG. 11A  is a perspective view of another embodiment of the molded filter frame of  FIGS. 10A and 10B  including spring-loaded or spring-biased hooks for attaching the frame directly to a grill of the fan.  FIG. 11B  is a close-up perspective view of a top corner of a rear face of the filter frame  74  of  FIG. 11A .  FIG. 11C  is a close-up view of a corner of a front face of the filter frame  74  of  FIG. 11A . In this embodiment, springs  92  are attached to the top corners of the filter frame  74 . A first end of each spring  92  is attached to the filter frame  74  at a spring seat  90 , for example in a press-fit relationship, or alternatively by a fastener or adhesive. A second end of each spring  92  extends through a corresponding hole  96  at each top corner of the filter frame. In this embodiment, the second ends of the springs  92  include integral hooks  94 . The hooks  94  are adapted to secure the filter frame  74  to the grate of the fan grill, and are shaped to interlock with features of common fan grills, for example rectangular openings and grates of the fan grill. The hooks  94  extend in a direction transverse to the longitudinal axes  101  of the channels  46 , and fingers  94 A at the ends of the hooks are configured to be inserted through an aperture in the fan grill and to latch a surface of the fan grill, for example an inner surface of a grate of the fan grill. In this manner, a top portion  89  of the filter frame  74  is removably secured to the fan body at the fan grill by a downward force of the springs  92 . The filter frame  74  further includes lower tabs  93  at a bottom region of the filter frame  74 . The lower tabs  93  can be integral with the filter frame  74  and can be molded on or otherwise attached to the filter frame  74 . The lower tabs  93  are adapted to secure the filter frame  74  to the fan grill and are shaped to extend from the filter frame  74  in a direction transverse to the longitudinal axes  101  of the channels  46  of the filter frame  74  so as to interlock with a feature of a common fan grill, for example the openings and grates of the fan grill. Lips, or other interlocking features, that extend from the lower tabs  93  are adapted to latch with the inner surfaces of the grates of the fan grill, through openings in the grate. The lower tabs  93  operate to counteract the downward force of the springs  92 . The tension between the springs  92  and the lower tabs  93  operates to retain the filter frame against the fan body  31 . The present spring-loaded hook and tab configuration is applicable to any of the filter frame embodiments described herein.  FIG. 11D  is a perspective view of the filter frame  74  of  FIG. 11A  mounted to a fan body  31 . Hooks  94  are inserted through apertures  75  of the fan grill and interlocked with the cross-members of the grate  73  of the fan grill  71 . Lower tabs  93  extend through apertures  75  of the fan grill and are latched with the inner surfaces of the grates  73  of the fan grill  71 . 
         [0102]      FIGS. 12A ,  12 B and  12 C are perspective views of another embodiment of the present invention.  FIG. 12A  is a perspective view of another embodiment of the molded filter frame  74  of  FIGS. 10A and 10B  including spring-loaded or spring-biased hooks.  FIG. 12B  is a close-up perspective view of a bottom corner of a rear face of the filter frame  74  of  FIG. 12A .  FIG. 12C  is a close-up of a top corner of a rear face of the filter frame  74  of  FIG. 12A . This embodiment is similar in structure and form to the embodiment of  FIG. 11  above, except that in this embodiment, the tabs  93  are at an upper portion of the filter frame  74  and the springs  92  are at lower portion of the filter frame  74 . In the present embodiment, the tabs  93  include fingers  99  that are oriented in a downward direction, and therefore, when inserted in a grate of a fan grill, through an opening in the grate, the tabs  93  bear the weight of the filter frame  74  and mounted filter. The springs  92  include upward-oriented hooks which, when engaged with the grate of the fan grill, operate to hold the filter frame  74  in place against the grill. Mounts  80  are also included at far left and right edges of the filter frame  74  for further mounting the frame to the fan body using optional elastic bands, as described above. The present embodiment can be applied to any of the filter frame embodiments described herein. 
         [0103]      FIGS. 13A-13E  are perspective views of another embodiment of the present invention in which a filter frame is integral with a fan grill of the fan body. Referring to  FIG. 13A , the grill  111  includes a latticed grate that includes cross members and openings. The grill  111  of the box fan  31  includes multiple side tabs  110  that form first and second side channels  118  and multiple bottom tabs  112  that form a base channel  119 . The side tabs  110  operate as retaining members for an inserted filter, and extend outwardly from the grill  111  surface in a direction transverse to a longitudinal axis of the first and second side channels  118 , and then in an inward direction toward a center of the grill. The bottom tabs  112  operate as stops for an inserted filter and, in the embodiment shown in  FIG. 13A , extend from the surface of the fan grill  111  in a manner similar to the side tabs  110 . The side and bottom tabs  110 ,  112  are molded with the grill  111  of the box fan  31 , such that the filter frame and the grill  111  of the box fan are unitary. The side tabs  110  and bottom tabs  112  in combination provide a slot or seat for securing an inserted filter to the grill  111  of the box fan  31 . The side channels  118  are spaced apart, as described above, and are dimensioned to provide a seat for receiving opposite edges of an inserted filter. The bottom tabs  112  operate as a stop at a bottom portion of the slot to provide a location for vertical positioning of the inserted filter. A top portion  89  of the slot provided by the filter frame is open to provide an insertion and removal location for the filter. With reference to  FIG. 13B , in an alternative embodiment, the side tabs  110  can be molded directly to the grill  111 . The side tabs  110  each include a first portion  110   a  that extends in an outward direction from the surface of the fan grill and a second portion  110   b  that extends from the first portion  110   a  in a direction toward a central region of the fan, for example L-shaped, so as to form a channel  118 . The tabs  110 ,  112  and underlying voids  111   a  are preferably shaped so as to accommodate a straight-pull injection molding process for forming the grill  111 , as described above.  FIG. 13C  is an exploded perspective view of an embodiment of a box fan and fan grill including an integral filter frame. The box fan has fan blades  117  and a motor for operating the fan blades  117 . A fan chassis surrounds the fan blades and motor. The fan grill shields the fan blades  117  and allows for air movement through the fan. The filter frame may be integral with the front grill, the rear grill, or both the front and rear grills of the box fan  31 . 
         [0104]    With reference to  FIG. 13D , the side tabs  110  are integral with the grill  111 . In this embodiment, the lowest side tabs  110  of the channels  118  are provided with bottom surfaces  114  that operate as a stop to prevent further insertion of the filter. Therefore, in this embodiment, additional bottom tabs are not necessary. 
         [0105]      FIG. 13E  is an assembled view of another embodiment of the grill  111  with an integrated filter frame including single, elongated, left and right side tabs  116  and a single bottom tab  120 , rather than multiple tabs as shown above. 
         [0106]    In one embodiment of a method of mounting a filter to a fan  31 , the method includes coupling the filter frame  32 ,  74  that has opposed first and second side channels  46 , each of the first and second side channels  46  having a longitudinal axis, to a grill  71  of a fan by couplers, for example elongated bolts  53  and wing nuts  64 , fasteners  18 , cable ties  69 , hooks  94  or tabs  93 , extending from the frame body in a direction transverse to the longitudinal axes of the first and second side channels  46 . The couplers engage a grate  73  of the grill  71  through an opening  75  in the grate. The first and second side channels  46  define a slot for insertion of an air filter. The slot has an upper portion  89  that allows for insertion and removal of an air filter, and a lower end that includes a stop  44 ,  106 ,  78 , for restricting further movement of an inserted air filter. An air filter  100 ,  102  is inserted into an upper end of the slot. Coupling the frame body to the grill of the fan optionally further includes coupling the frame body to the grate  73  of the grill of the fan using at least one tab  93  extending from the frame body  32 ,  74 . Further, coupling the frame body  32 ,  74  to the grill of the fan optionally further includes coupling the frame body to the grate  73  of the grill of the fan using at least one hook  94  extending from the frame body  32 ,  74 . 
         [0107]    In another embodiment of a method of mounting a filter to a fan  31 , the method includes coupling a frame body  32 ,  74  having opposed first and second side channels  46  to a grill of a fan by at least one elastic band  33 ,  38 ,  25   a ,  25   b  extending about a portion of a fan chassis so that when installed, tension in the at least one elastic band  33 ,  38 ,  25   a ,  25   b  operates to secure the frame body to the fan  31 . The first and second channels  46  define a slot for insertion of an air filter. The slot has an upper portion  89  that allows for insertion and removal of an air filter, and a lower end that includes a stop  44 ,  106 ,  78  for restricting further movement of an inserted air filter. An air filter  100 ,  102  is inserted into an upper end of the slot. 
         [0108]    In another embodiment, a method for forming a grill  111  for a fan  31  comprises forming a latticed grate including cross members and openings and having an inner surface and an outer surface. The method further includes forming retaining members  110 ,  116  extending from the outer surface of the grate in a direction transverse to the outer surface at first and second outer regions of the grill  111  to define opposed first and second side channels  118 . The first and second side channels  118  define a slot for insertion of an air filter. The slot has an upper end that allows for insertion and removal of an air filter, and a lower end that includes a stop  112 ,  114 ,  120  for restricting further movement of an inserted air filter. The grill  111  is mounted to a fan chassis. 
         [0109]    In this manner, the present invention provides a filter frame that can be readily mounted to and removed from a chassis of a fan, without causing permanent disfigurement of the fan body. In addition, the present invention provides a filter frame that is integrated into the grill of the frame, to further ease the application of a filter to a fan. 
         [0110]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.