Patent Publication Number: US-2021187425-A1

Title: Air filter devices with gap sealing unit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 15/762,409, filed 13 Aug. 2018, which is a national stage filing under 35 U.S.C. 371 of PCT/US2016/052047, filed 16 Sep. 2016, which claims the benefit of U.S. Provisional Application No. 62/222,836, filed 24 Sep. 2015, the disclosures of which are incorporated by reference in their entireties herein. 
    
    
     BACKGROUND 
     The present disclosure relates to air filters. More particularly, it relates to expandable air filters, such as expandable HVAC air filters, appropriate for use with multiple, differently sized air filter compartments. 
     Air filters are commonly used in forced air systems (e.g., residential heating, ventilation and air conditioning (HVAC) systems) in order to remove dust, dirt particles and the like. With many HVAC installations, a disposable air filter is conventionally employed. Such air filters typically include a filter media surrounded and supported by an outer frame. In addition to supporting the filter media, the outer frame rigidly defines a perimeter size and shape of the air filter. Other supporting and/or reinforcing components, such as mesh screens, adhesive beads, etc., may also be included. After a period of use, these filters become dirty or clogged and must be replaced. 
     To facilitate air filter replacement, HVAC systems conventionally house the air filter within a user-accessible compartment. The air filter is placed into and/or retrieved from the compartment via an access slot. In some instances, the air filter alone is inserted through the slot. In other instances, a separate cabinet is provided into which the air filter is placed, followed by insertion of the loaded cabinet through the slot. In all instances, upon final insertion, a seal is desirably established between the outer frame of the air filter and framework of the compartment so as to prevent airflow around the air filter during use (and thus prevent un-filtered airflow from passing through the HVAC system). Preferred replacement air filters have a size that corresponds with the expected size (in terms of height, width and depth) of the HVAC system&#39;s air filter compartment. 
     A number of “standard” HVAC air filter compartment sizes have gained industry acceptance over time and are widely employed. Replacement air filter manufacturers, in turn, attempt to make available for retail purchase air filters corresponding with these standard sizes, allowing a customer to select a particular air filter that should fit their HVAC system&#39;s compartment configuration. The rigid outer frame of conventional air filters dictates that the replacement air filter has the same size when shipped to a retailer, when presented to potential purchases, and when installation to the HVAC system is attempted. Because these typical HVAC air filters are thus rather bulky, they undesirably occupy a relatively large volume of space on transportation vehicles and retailer shelves. Further, where the retailer has limited available shelf space and/or desires to display for purchase a large number of differently-sized air filters, only a small number of larger-sized air filters (e.g., deep pleat air filters) can reasonably be presented on the retailer&#39;s shelving system. When the small number of a certain air filter size are subsequently removed from the shelf for purchase and the retailer does not consistently replenish the display shelf, it may undesirably appear to the next potential purchaser that the particular air filter size of interest is out of stock. 
     In addition, a potential customer may not immediately recall with confidence the correct air filter size for their HVAC system while at the retailer&#39;s place of business; this uncertainty can be exacerbated when a large number of different air filter sizes are displayed. Rather than purchase a potentially incorrectly-sized air filter, the consumer will instead decide to delay air filter replacement to a later date, potentially leading to inefficient operation of the HVAC system if a new air filter is not actually purchased for an extended period of time. 
     Moreover, the actual air filter compartment size associated with a particular HVAC system will oftentimes deviate from the designated “standard” or expected size. For example, the HVAC system manufacturer&#39;s specifications may identify an air filter size of 16″×20″×4″, yet the actual air filter compartment is slightly smaller or slightly larger in one or more dimensions. Thus, a purchased 16″×20″×4″ replacement air filter may not be an optimal fit for the actual HVAC system compartment (e.g., the purchased air filter may be too large for straightforward insertion, or may be too small and lead to suboptimal HVAC system operation). These circumstances can be frustrating for the user, and can lead to even greater uncertainty when considering the next replacement air filter purchase. 
     The above-described concerns with conventional replacement HVAC air filters can also arise in other contexts. Many other types of air handling devices or systems (e.g., room air purifiers, window air filters, etc.) make use of a replaceable, rigid-frame air filter, and a plethora of differently-sized replacement air filters are presented for retail purchase. Once again, the relatively large number of differently-sized air filters that must be displayed occupies valuable retail shelf space, and a potential purchaser will oftentimes be unsure as to which size is a best “fit” at the time of purchase. 
     SUMMARY 
     The inventors of the present disclosure recognize that a need exists for an air filter that overcomes one or more of the above-mentioned problems. 
     Some aspects of the present disclosure relate to an air filter device including an air filter unit and an expansion unit. The air filter unit includes a filter media assembly maintained by an outer frame assembly. The outer frame assembly defines exterior length, width and depth dimensions of the air filter device in an initial state. The expansion unit provides one or more of an expanded length, width or depth in an expanded state of the air filter device. In some embodiments, portions or an entirety of the expansion unit is provided apart from the air filter unit in a deliver condition of the air filter device (e.g., the air filter device can be provided in kit form to a user). In other embodiments, portions or an entirety of the expansion unit is assembled to the air filter unit prior to delivery to a user. Regardless, the air filter devices of the present disclosure are useful with a wide variety of differently size air handling devices, able to readily fit and seal with a compartment of the air handling device via the expansion unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a perspective view of an air filter device in accordance with principles of the present disclosure, including portions shown in block form; 
         FIG. 2A  is a perspective view of the air filter device of  FIG. 1  in an initial state; 
         FIGS. 2B-2D  are perspective views of the air filter device of  FIG. 1  in various expanded states; 
         FIG. 3A  is a perspective view of a filter media assembly useful with the air filter device of  FIG. 1A ; 
         FIG. 3B  is a side view of a portion of the filter media assembly of  FIG. 3A ; 
         FIG. 4A  is a perspective view of an air filter device in accordance with principles of the present disclosure; 
         FIG. 4B  is an enlarged view of a portion of the air filter device of  FIG. 4A ; 
         FIG. 5A  is a perspective view of an air filter device in accordance with principles of the present disclosure; 
         FIG. 5B  is an enlarged view of a portion of the air filter device of  FIG. 5A ; 
         FIG. 6A  is a perspective view of an air filter device in accordance with principles of the present disclosure; 
         FIG. 6B  is an enlarged view of a portion of the air filter device of  FIG. 6A ; 
         FIG. 7A  is a perspective view of an air filter device in accordance with principles of the present disclosure; 
         FIG. 7B  is an enlarged view of a portion of the air filter device of  FIG. 7A ; 
         FIG. 8A  is a perspective view of an air filter device in accordance with principles of the present disclosure; 
         FIG. 8B  is an enlarged view of a portion of the air filter device of  FIG. 8A ; 
         FIG. 9A  is a perspective view of an air filter device in accordance with principles of the present disclosure; 
         FIG. 9B  is an enlarged view of a portion of the air filter device of  FIG. 9A ; 
         FIG. 10A  is a perspective view of an air filter device in accordance with principles of the present disclosure; and 
         FIG. 10B  is an enlarged view of a portion of the air filter device of  FIG. 10A . 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present disclosure relate to air filter devices that readily fit, and achieve a desired seal within, differently-sized air handling compartments. One embodiment of an air filter device  20  in accordance with principles of the present disclosure is shown in  FIG. 1  and includes an air filter unit  22  and an expansion unit  24  (shown in block form). The air filter unit  22  can be akin to any conventional or known air filter (e.g., HVAC air filter), and includes a filter media assembly  30  and an outer frame assembly  32  as described below. The outer frame assembly  32  can establish exterior dimensions of the air filter unit  22 , including exterior dimensions in length L, width W, and depth D directions. The expansion unit  24  can assume a wide variety of forms as described below, and generally serves to selectively increase a footprint or size of the air filter unit  22  in one or more of the length L, width W and depth D directions. The air filter device  20  is generally constructed to have an initial state as initially provided to a user in which some or all of the expansion unit  24  is separate from the air filter unit  22 , or, if connected to the air filter unit  22  in the initial state, the expansion unit  24  (or corresponding portions thereof) is retracted so as to not overtly extend outside the footprint established by the outer frame assembly  32 .  FIG. 2A  is a non-limiting example of the initial state of the air filter device  20  in which a portion or entirety of the expansion unit  24  ( FIG. 1 ) is apart from the air filter unit  22 , and the air filter unit  22  alone (or with the optional portion of the expansion unit  24  in a retracted arrangement) serves as the air filter device  20  for installation to an air handling system (not shown). In the initial state, then, the air filter device  20  has length L I , width W I  and depth D I  dimensions as dictated by the air filter unit  22 , for example by the outer frame assembly  32 . Where desired by a user, the expansion unit  24  can be installed and/or deployed relative to the air filter unit  22 , to generate an expanded state of the air filter device  20 . The air filter device  20  can be installed to an air handling system in the expanded state (and/or be caused to transition to the expanded state following installation). As generally reflected by the non-limiting example expanded states of  FIGS. 2B-2D , the expanded state of the air filter device  20  of the present disclosure can include an expanded length L E  ( FIG. 2B ), an expanded width W E  ( FIG. 2C ) and/or an expanded depth D E  ( FIG. 2D ) that is greater than the corresponding dimension L I , W I , D I  in the initial state. 
     Returning to  FIG. 1 , in some embodiments, the air filter unit  22  is sized for installation to a conventional HVAC system, with at least the outer frame assembly  32  supporting the filter media assembly  30  in the presence of HVAC system airflow. With these non-limiting constructions, depending upon a size of the air filter compartment provided with the HVAC system, a user can install the air filter unit  22  alone (i.e., the air filter device  20  in the initial state as described above), or can utilize the expansion unit  24  to expand the air filter device  20  in one or more directions to better match an actual size of the air filter compartment, better ensuring a desired seal is achieved between the air filter device  20  and framework of the compartment. 
     With embodiments in which the initial state of the air filter device  20  includes a portion or an entirety of the expansion unit  24  not directly attached or connected to the air filter unit  22 , the air filter device  20  can optionally be provided to a user in kit form. For example, the air filter unit  22  and the expansion unit  24  can be commonly packaged within a container or other packaging, optionally with one or more additional items such as written instructions for use. The packaging can assume any useful format, for example packaging useful for retail display and sale. 
     Air Filter Unit 
     The air filter unit  22  can assume various forms, and can include the filter media assembly  30  and the outer frame assembly  32 . The filter media assembly  30  can assume a wide variety of forms useful for air filtration, such as HVAC air filtration, presently known, or in the future developed. In some embodiments, the filter media assembly  30  is a pleated filter media assembly. By “pleated” is meant a web at least a portion of which has been folded to form a configuration comprising rows of generally parallel, oppositely oriented folds. For example, and as shown in  FIGS. 3A and 3B , a pleated version of the filter media assembly  30  includes a plurality of pleats  40  each including a fold line  42  defining a pleat tip  44  and a pair of adjacent panels  46 . 
     The pleated version of the filter media assembly  30  can consist of a pleated filter media or web  60  alone (as in the illustrated embodiment), or can include one or more additional components or structures applied or assembled to a pleated filter media  60 . The pleated filter media  60  of the assembly  30  can be self-supporting or non-self-supporting. As used herein, the term “self-supporting filter media or web” can describe at least one of the following conditions: (1) a filter media or web that is deformation resistant without requiring stiffening layers, adhesive or other reinforcement in the filter media web; or (2) the filter media generally maintains its shape when subjected to an airstream as described, for example, in U.S. Pat. No. 7,169,202 to Kubokawa, the entire teachings of which are incorporated herein by reference; or (3) a web or media having sufficient coherency and strength so as to be drapable and handleable without substantial tearing or rupture. As used herein, the term “non-self-supporting” can denote an air filter media that is not capable, in the absence of a support frame and/or a support grill, of withstanding the forces encountered due to typical air flow. For example, where the pleated version of the filter media assembly  30  consists of the pleated filter media  60  alone, the pleated filter media or web  60  can be self-supporting or non-self-supporting. Where the pleated version of the filter media assembly  30  consists of the pleated filter media or web  60  and a support structure, the pleated filter media  60  can be non-self-supporting with the additional supporting structure rendering the pleated filter media assembly  30 , as a whole, to be self-supporting. 
     The particular filter media  60  selected for the pleated version of the filter media assembly  30  is not critical to the present disclosure so long as the resultant pleated filter media assembly  30  (whether consisting solely of the pleated filter media  60  alone or with additional structures applied thereto) has the desired characteristics described herein. The filter media  60  can be constructed, for example, from nonwoven fibrous media formed of thermoplastics or thermosetting materials such as polypropylene, linear polyethylene and polyvinyl chloride. Other suitable, non-limiting materials for the filter media include porous foams, nonwovens, papers, fiberglass, or the like. The filter media assembly  30  can optionally include a highly open wire mesh or screen, one or more adhesive strands, etc., that is bonded to the filter media  60  in order to enhance the pleatability thereof and that is pleated along with the filter media  60  itself. The wire mesh or screen (or other additional component) may impede re-collapsing of the pleated version of the filter media assembly  30 . In other embodiments, the pleated version of the filter media assembly  30  can incorporate wire-supported pleats, self-supported mini-pleats, or other pleat constructions currently available or in the future developed. 
     In some embodiments, the filter media  60  comprises a nonwoven web that can have random fiber arrangement and generally isotropic in-plane physical properties (e.g., tensile strength), or if desired may have aligned fiber construction (e.g., one in which the fibers are aligned in the machine direction as described in U.S. Pat. No. 6,858,297 to Shah et al., the teachings of which are incorporated herein by reference) and anisotropic in-plane physical properties. Some or all of the fibers comprising the nonwoven webs useful with the filter media  60  can be multicomponent fibers having at least a first region and a second region, where the first region has a melting temperature lower than the second region. Some suitable multicomponent fibers are described, for example, in U.S. Pat. Nos. 7,695,660, 6,057,256, 5,597,645, 5,972,808, 5,662,728 and 5,486,410 the teachings of each of which are incorporated herein by reference in their entireties. 
     Other nonwoven webs useful with the filter media  60  can be a high loft spunbond web, such as described, for example, in U.S. Pat. No. 8,162,153 to Fox et al., the entire teachings of which are incorporated herein by reference. In other embodiments, the filter media  60  can be a low loft spunbond web, such as those described in U.S. Pat. No. 7,947,142 to Fox et al., the entire teachings of which are incorporated herein by reference. In yet other embodiments, nonwoven webs useful with the filter media  60  are generated by other techniques and/or have other characteristics, such as the meltblown nonwoven webs disclosed in U.S. Pat. No. 6,858,297 to Shah et al. (mentioned above). Other non-limiting example of useful nonwoven web formats include bi-modal fiber diameter meltblown media such as that described in U.S. Pat. No. 7,858,163, the entire teaching of which are incorporated herein by reference. 
     In some embodiments, an electrostatic charge is optionally imparted into or on to material(s) of the filter media  60 . Thus, the filter media  60  can be an electret nonwoven web. Electric charge can be imparted to the filter media  60  in a variety of ways as is well known in the art, for example by hydrocharging, corona charging, etc. (e.g., as described in U.S. Pat. No. 7,947,142 (mentioned above)). In other embodiments, the filter media  60  is not electrostatically charged. 
     The optional pleats can be formed in the filter media  60  (or in the pleated filter media assembly  30 ) using various methods and components as are well known in the art, e.g., to form a pleated filter for use in applications such as air filtration, for example those described in U.S. Pat. No. 6,740,137 to Kubokawa et al. and U.S. Pat. No. 7,622,063 to Sundet et al., the entire teachings of both of which are incorporated herein by reference. 
     With pleated versions of the filter media assembly  30 , a variety of pleat depths D can be incorporated. In some embodiments, the pleated filter media assembly  30  has a pleat depth D of at least about 4 inches, optionally not less than 4 inches (e.g., a “deep pleat” pleated filter media). Other depths, greater or smaller, are also acceptable. 
     In other embodiments of the present disclosure, portions or all of the filter media assembly  30  need not have a pleated construction. 
     Regardless of an exact construction, the filter media assembly  30  defines opposing, first and second major faces  70 ,  72  (referenced generally in  FIGS. 3A and 3B ). Further, a perimeter of the filter media assembly can be defined by opposing, first and second side edges  80 ,  82 , and opposing, first and second end edges  84 ,  86 . In some embodiments, the perimeter can have the rectangular shape (that is specifically inclusive of a square shape) shown. 
     Returning to  FIG. 1 , the outer frame assembly  32  can assume a variety of forms and is generally configured to surround the perimeter of the filter media assembly  30 . Further, the outer frame assembly  32  is constructed to robustly support the filter media assembly  30  in the initial state as well as in any of the expanded states described below, including the outer frame assembly  32  rigidly maintaining the established length L I , width W I , and depth D I  ( FIG. 2A ) dimensions when subjected to expected forces of a designated end-use environment (e.g., the outer frame assembly  32  will maintain its structural integrity with installation to an HVAC system air filter compartment and subjecting the air filter device  20  to normal HVAC system airflow). With this in mind, the outer frame assembly  32  includes or defines opposing, first and second side frame structures  100  (one of which is visible in  FIG. 1 ) and opposing, first and second end frame structures  104  (one of which is visible in  FIG. 1 ). The side frame structures  100  are generally configured to cover a respective one of the first and second side edges  80 ,  82  ( FIG. 3A ) of the filter media assembly  30 , whereas the end frame structures  104  are generally configured to cover a respective one of the first and second end edges  84 ,  68  ( FIG. 3A ). 
     The frame structures  100 ,  104  can have any format conducive to use as part of the outer frame assembly  32 , and in some embodiments can be substantially identical. For example, in some embodiments, one or more or all of the frame structures  100 ,  104  can consist of a single frame member or body. In other embodiments, one or more or all of the frame structures  100 ,  104  can include two or more frame members that connected to another (e.g., slidably connected). 
     The outer frame assembly  32  can be formed from a variety of materials capable of maintaining their structural integrity in the presence of expected forces. For example, the outer frame assembly  32  can be constructed of cardboard, paperboard, plastic, metal, etc. In some embodiments, the outer frame assembly  32  integrally forms the side and end frame structures  100 ,  104 . Thus, in some embodiments a major portion of the outer frame assembly  32  may be conveniently formed by the folding of a suitable precursor material (e.g., paperboard) along fold lines so as to provide the side and end frame structures  100 ,  104 . However, any suitable frame construction may be used; i.e. any major portion of the outer frame assembly  32  may be made of any suitable material (whether paperboard, plastic, etc.) and may be formed e.g. by folding of a single frame piece, by the assembling of multiple pieces to each other, and so on. In many embodiments, all four major frame structures  100 ,  104  may each comprise upstream and downstream flanges and inner and outer sidewalls/panels and foldable connections there between. 
     In some embodiments, the air filter unit  22  can further include one or more grid or grill structures extending over a corresponding one of the major faces  70 ,  72  ( FIGS. 3A and 3B ) of the filter media assembly  30 . For example,  FIG. 1  illustrates a grid or grill  120  projecting from the outer frame assembly  32  and extending over the first major face  70  (best identified in  FIG. 3B ) of the filter media assembly  30 . The pattern reflected by  FIG. 1  for the grid or grill  120  is but one acceptable configuration. The air filter unit  22  can optionally include an additional grill or grid structure (not shown) overlying the second major face  72  (hidden in  FIG. 1 , but identified, for example, in  FIG. 3B ) of the filter media assembly  30 . Regardless, the grill(s) or grid(s)  120  can be formed of a material similar to that of the outer frame assembly  32 . In some embodiments, the grill(s) or grid(s)  120  can be integrally formed with, and folded relative to, the outer frame assembly  32 . In other embodiments, the grill(s) or grid(s) (or sub-components thereof) can be separately formed and subsequently attached to the outer frame assembly  32 . 
     Expansion Unit 
     The expansion unit  24  can assume a variety of forms compatible with the particular format of the air filter unit  22 . One or more portions of, or an entirety of, the expansion unit  24  can be provided as component of (e.g., pre-assembled to) the air filter unit  22 ; in other embodiments, an entirety of the expansion unit  24  can be provided apart from the air filter unit  22  and subsequently assembled thereto by a user. Various examples of expansion units in accordance with principles of the present disclosure are described below. While described separately, portions or an entirety of one example expansion unit can be combined with portions or an entirety of another example expansion unit. 
     An air filter device  220  including an example expansion unit  224  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 4A and 4B . As a point of reference,  FIGS. 4A and 4B  reflect a possible installation condition of the air filter device  220  in which the expansion unit  224  (or portions thereof) has been mounted to the air filter unit  22 . Conversely, a possible delivery condition (not shown) of the air filter device  220  includes the expansion unit  224  not yet mounted to the air filter unit  22  (e.g., a user can receive the air filter device  220  in the delivery condition, and then mount the expansion unit  224  (or portions thereof) to the air filter unit  22  in achieving the possible installation condition). 
     The expansion unit  224  includes one or more standoffs  230 . The standoffs  230  are generally sized and shaped for mounting to a designated region of the air filter unit  22 , and can include one or more of a length standoff  230 A, a width standoff  230 B, and a depth standoff  230 C. The length standoff  230 A is generally sized and shaped for mounting to one of the end frame structures  104  to effectuate an expanded state length L E  that is greater than the initial state length L I  ( FIG. 1 ). The width standoff  230 B is generally sized and shaped for mounting to one of the side frame structures  100  to effectuate an expanded state width W E  in the air filter device that is greater than the initial state width W I  ( FIG. 1 ). Finally, the depth standoff  230 C is generally sized and shaped for mounting to outer frame assembly  32  or other component of the air filter unit  22  at a location that does not overtly impede airflow through the air filter unit  22  (e.g., at a corner formed by two of the frame structures  100 ,  104 , on the grill or grid  120 , etc.) to effectuate an expanded state depth D E  that is greater than the initial state depth D I  ( FIG. 1 ). In some embodiments, the expansion unit  224  as provided to a user in the delivery condition mentioned above can include one (or more) of the length standoff  230 A, one (or more) of the width standoff  230 B, and a plurality of the depth standoffs  230 C. In other embodiments, the expansion unit  224  as provided to a user in the delivery condition can include less than all of the length standoff  230 A, the width standoff  230 B and/or the depth standoffs  230 C (e.g., the expansion unit can include only the depth standoffs  230 C). 
     Each of the standoffs  230  can have a similar construction, for example including a standoff body  240  (identified, for example, for the length standoff  230 A in  FIG. 4B ). In some embodiments, the standoff body  240  can be formed of a light weight, resilient, at least slightly compressible material capable of maintaining a designated shape when subjected to compression. For example, the standoff body  240  can be a foam material (e.g., open or closed cell foams, natural foams, synthetic foams, etc.). Other materials, such as rubber, plastic, etc., are also envisioned. In some embodiments, the standoff body  240  associated with each of the standoffs  230 A- 230 C is a pre-cut foam strip (e.g., as with the standoffs  230 A,  230 B) or block (e.g., a cylindrical block as with the standoffs  230 C), sized and shaped in accordance with geometries of the corresponding air filter unit  22  as described above. 
     Each of the standoffs  230  can further be configured to promote mounting thereof to the air filter unit  22  by a user. For example, a face of the standoff body  240  can carry (e.g., be coated with) an adhesive formulated to achieve a bond between the standoff body  240  and a corresponding portion of the air filter unit  22  (e.g., where the outer frame assembly  32  is a paperboard material, the selected adhesive can be formulated to achieve a bond with paperboard). As initially provided to a user (e.g., as part of a kit in which the standoff(s)  230  are provided to a user apart from the air filter unit  22 ), a release liner can further be included, temporarily covering the adhesive. When the user is ready to mount the standoff  230  to the air filter unit  22 , the release liner is removed thereby exposing the adhesive. In other embodiments, one or more adhesive strips (not shown) can be provided on the outer frame assembly  32  (or other exterior components of the air filter unit  22 ) at location(s) corresponding with potential application of a standoff  230 ; under these circumstances, the adhesive strip(s) can be temporarily covered by a release liner that is removed prior to mounting of the corresponding standoff  230 . In yet other embodiments, a strip of double sided tape (that may be provided to the user as part of the expansion unit  224 ) can be employed to secure the standoff(s)  230  to the air filter unit  22 . Other configurations that facilitate mounting of the standoff  230  to the air filter unit  22  are also acceptable (e.g., a mechanical fastener, hook-and-loop fasteners, etc.). 
     During use, the air filter device  220  is initially provided to a user in an initial state in which the air filter unit  22  is separated from the expansion unit  224 . For example, the air filter unit  22  and the expansion unit  224  can be provided to a user in a common packaging, with none of the standoffs  230  mounted to the air filter unit  22 . Alternatively, a user can obtain (e.g., purchase) the air filter unit  22  and the expansion unit  224  separately. Regardless, the user then evaluates (e.g., visually estimates) dimensions of the air filter compartment (not shown) to which the air filter device  220  will be installed. In some instances, dimensions of the air filter unit  22  will closely correspond to the dimensions of the air filter compartment. Under these circumstances, the air filter unit  22  alone can be installed to the air filter compartment (e.g., the air filter unit  22  serves as the installed air filter device  220 ). In other instances, the user may determine that one or more of the length L I , width W I  and/or depth D I  ( FIG. 2A ) dimension of the air filter unit  22  is appreciably less (e.g., 10% less) than the corresponding dimension of the air filter compartment. Under these circumstances, the user can select and mount one or more of the standoffs  230  to air filter unit  22 , effectuating a desired increase in the corresponding dimension. For example, if it is determined that the depth D I  of the air filter unit  22  is appreciable less than the depth dimension of the air filter compartment, one or more of the depth standoffs  230 C can be mounted to the air filter unit  22  as shown, for example, in  FIG. 4A . Additionally or alternatively, the length standoff  230 A can be selected and mounted to the air filter unit  22  to effectuate an increased or expanded length L E , and the width standoff  230 B can be selected to the air filter unit  22  to effectuate an increased or expanded width W E . It will be understood that for a particular air filter compartment installation, less than all of the standoffs  230 A- 230 C may be required. Once the selected standoff(s)  230  have been mounted to the air filter unit  22  so as to transition the air filter device  220  to an expanded state, the air filter device  220  can be installed to the air filter compartment, with the mounted standoff(s)  230  bearing against framework of the air filter compartment and promoting a seal between the air filter device  220  and the air filter compartment. 
     Another air filter device  320  including an example expansion unit  324  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 5A and 5B . As a point of reference,  FIGS. 5A and 5B  reflect a possible installation condition of the air filter device  320  in which the expansion unit  324  (or portions thereof) has been mounted to the air filter unit  22 . Conversely, a possible delivery condition (not shown) of the air filter device  320  includes the expansion unit  324  not yet mounted to the air filter unit  22  (e.g., a user can receive the air filter device  320  in the delivery condition, and then mount the expansion unit  324  (or portions thereof) to the air filter unit  22  in achieving the possible installation condition). In yet other embodiments, the delivery condition of the air filter device  320  includes the expansion unit  324  (or portions thereof) pre-assembled to (or integrally formed by) the air filter unit  22 . With some of these embodiments, the pre-assembled expansion unit  324  (or portions thereof) is configured to self-deploy to the expanded condition reflected by  FIGS. 5A and 5B  in the presence of airflow as described below. 
     The expansion unit  324  includes one or more flanges  330 . The flanges  330  are generally sized and shaped in accordance with a designated region of the air filter unit  22 , and can include one or more of a length flange  330 A and one or more of a width flange  330 B. The length flange  330 A is generally sized and shaped in accordance with dimensions of one of the end frame structures  104  to effectuate an expanded state length L E  that is greater than the initial state length L I  ( FIG. 1 ). The width flange  330 B is generally sized and shaped in accordance with dimensions of one of the side frame structures  100 ,  102  to effectuate an expanded state width W E  that is greater than the initial state width W I  ( FIG. 1 ). In some embodiments, the expansion unit  324  can include both of the length and width flanges  330 A,  330 B; in other embodiments, the expansion unit  324  includes only the length flange  330 A or only the width flange  330 B. 
     Apart from dimensions, each of the flanges  330  can have a similar construction. For example, and as identified for the length flange  330 A in  FIG. 5B , each of the flanges  330  can be a lightweight yet relative stiff material defining a fixed end  340  opposite a free end  342 . The fixed end  340  can be connected to, or is configured for connection to by a user, the corresponding frame structure of the air filter unit  22  (e.g., the fixed end  340  of the length flange  330 A is connected to the fend frame structure  104 ) in a manner permitting pivoting movement at the point or line of connection. The flange  330  projects away from the fixed end  340 , terminating at the free end  342  that is otherwise free of direct connection or attachment to the air filter unit  22 . For example, in some embodiments the flange  330  is a paperboard body integrally formed with the outer frame assembly  32 , with a fold line being formed at the line of interface between the flange  330  and the corresponding frame structure  100 ,  104  of the outer frame assembly  32  to define the fixed end  340 . 
     With embodiments in which the air filter device  320  is provided to a user with the flange(s)  330  pre-assembled to (e.g., integrally formed with) the air filter unit  22 , the user installs the air filter device  320  (including the flange(s)  330 ) to the air filter compartment (not shown). With embodiments in which the air filter device  320  is provided to a user with the flange(s)  330  uncoupled from the air filter unit  22 , the user can first compare an estimated size of the air filter compartment with the length and width L I , W I  dimensions of the air filter unit  22 . Based on this comparison, one or both of the flanges  330 A,  330 B can be mounted to the air filter unit  22  as described above, with the so-configured air filter device  320  then being installed to the air filter compartment. In either instance, the air filter device  320  can be installed such that the free end  342  of the flange(s)  330  faces the upstream direction of airflow through the air filter compartment. During operation of the air handling device, airflow (designated by arrow F in  FIG. 5A ) will interface between the flange(s)  330  and the outer frame assembly  32 , forcing the flange(s)  330  to extend outwardly relative to the outer frame assembly  32  (e.g., the flange(s)  330  is caused to pivot relative to the outer frame assembly  32  at the fixed end  340 , with the corresponding free end  342  moving outwardly away from the outer frame assembly  32 ). In this expanded state, the flange(s)  330  can be brought into contact with framework of the air filter compartment, promoting a seal between the air filter device  320  and the air filter compartment. 
     Another air filter device  420  including an example expansion unit  424  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 6A and 6B . As a point of reference,  FIGS. 6A and 6B  reflect a possible installation condition of the air filter device  420  in which the expansion unit  424  (or portions thereof) has been mounted to the air filter unit  22 . Conversely, a possible delivery condition (not shown) of the air filter device  420  includes the expansion unit  424  (or portions thereof) not yet mounted to the air filter unit  22  (e.g., a user can receive the air filter device  420  in the delivery condition, and then mount the expansion unit  424  (or portions thereof) to the air filter unit  22  in achieving the possible installation condition). In yet other embodiments, the delivery condition of the air filter device  420  includes the expansion unit  424  (or portions thereof) pre-assembled to (or integrally formed by) the air filter unit  22 . With some of these embodiments, the pre-assembled expansion unit  424  (or portions thereof) is configured to self-deploy to the expanded condition reflected by  FIGS. 6A and 6B , optionally in the presence of airflow as described below. 
     The expansion unit  424  can be akin to the expansion unit  324  ( FIGS. 5A and 5B ) described above, and includes one or more the flanges  330  (e.g., the length flange  330 A and the width flange  330 B). In addition, the expansion unit  424  includes one or more deflection bodies  430  associated with a corresponding one of the flanges  330  (e.g., with the non-limiting example of  FIGS. 6A and 6B , the expansion unit  424  includes a first deflection body  430 A corresponding with the length flange  330 A and a second deflection body  430 B corresponding with the width flange  330 B). Apart from dimensions, each of the deflection bodies  430  can have a similar construction. For example, each of the deflection bodies  430  can be formed of a light weight, resilient, at least slightly compressible material capable of maintaining a designated shape when subjected to compression. In some embodiments, the deflection bodies  430  can be a foam material (e.g., open or closed cell foams, natural foams, synthetic foams, etc.). Other materials, such as rubber, plastic, etc., are also envisioned. In some embodiments, the deflection bodies  430  can each be a pre-cut foam strip, sized and shaped in accordance with geometries of the corresponding air filter unit  22  components (e.g., the first deflection body  430 A is pre-cut to a size and shape corresponding with dimensions of one of the end frame structures  104 ; the second deflection body  430 B is pre-cut to a size and shape corresponding with dimensions of one of the side frame structures  100 ). 
     In some embodiments, the air filter device  420  is provided to a user with the deflection bodies  430  pre-assembled to the air filter unit  22 . In other embodiments, the delivery condition of the air filter device  420  can include the deflection bodies  430  apart from the air filter unit  22  (it being recalled that the flanges  330  may or may not be assembled to the air filter unit  22  in the delivery condition). With these configurations, the expansion unit  424  can further include one or more strips of double-sided adhesive tape or other fastening devices (e.g., complimentary strips of hook-and-loop fasteners) that are employed by a user to secure the deflection bodies  430  at the locations shown. Alternatively, the deflection bodies  430  can be coated with an adhesive that is temporarily covered by a release liner, the air filter unit  22  can be coated with an adhesive at desired locations and that are temporarily covered by a release liner, etc. 
     With embodiments in which the air filter device  420  is provided to a user with the flange(s)  330  and the deflection body/bodies  430  pre-assembled to the air filter unit  22 , the user installs the air filter device  420  to the air filter compartment (not shown). With embodiments in which the air filter device  320  is provided to a user with the deflection body/bodies  430  uncoupled from the air filter unit  22 , the user can first compare an estimated size of the air filter compartment with the length and width L I , W I  dimensions of the air filter unit  22 . Based on this comparison, one or both of the deflection bodies  430 A,  430 B can be mounted to the air filter unit  22  as described above, with the so-configured air filter device  420  then being installed to the air filter compartment. In either instance, the air filter device  420  can be installed such that the free end  342  of the flange(s)  330 A,  330 B faces the upstream direction of airflow through the air filter compartment. During operation of the air handling device, airflow (designated by arrow F in  FIG. 6A ) will progress between each of the flanges  330 A,  330 B and the outer frame assembly  32 , forcing the flange(s)  330  to extend outwardly relative to the outer frame assembly  32  as described above. The deflection body (where provided)  430  biases the corresponding flange  330  such that the free end  342  projects away from the outer frame assembly  32 , and prevents the corresponding flange  330 A,  330 B from collapsing on to the outer frame assembly  32 . Once again, in this expanded state, the flange(s)  330 A,  330 B can be brought into contact with framework of the air filter compartment, promoting a seal between the air filter device  420  and the air filter compartment. 
     Another air filter device  520  including an example expansion unit  524  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 7A and 7B . As a point of reference,  FIGS. 7A and 7B  reflect a possible installation condition of the air filter device  520  in which the expansion unit  524  (or portions thereof) has been mounted to the air filter unit  22 . Conversely, a possible delivery condition (not shown) of the air filter device  520  includes the expansion unit  524  not yet mounted to the air filter unit  22  (e.g., a user can receive the air filter device  520  in the delivery condition, and then mount the expansion unit  524  (or portions thereof) to the air filter unit  22  in achieving the possible installation condition). In yet other embodiments, the delivery condition of the air filter device  520  includes the expansion unit  524  (or portions thereof) pre-assembled to (or integrally formed by) the air filter unit  22 . With some of these embodiments, the pre-assembled expansion unit  524  (or portions thereof) is configured to self-deploy to the expanded condition reflected by  FIGS. 7A and 7B  in the presence of airflow as described below. 
     The expansion unit  524  includes one or more flanges  530  that can be akin to the flanges  330  ( FIG. 5A ) described above. The flanges  530  are generally sized and shaped in accordance with a designated region of the air filter unit  22 , and can include one or more of a length flange  530 A and one or more of a width flange  530 B. The length flange  530 A is generally sized and shaped in accordance with dimensions of one of the end frame structures  104  to effectuate an expanded state length L E  (not specifically identified in  FIGS. 7A and 7B  for ease of illustration) that is greater than the initial state length L I  ( FIG. 1 ). The width flange  530 B is generally sized and shaped in accordance with dimensions of one of the side frame structures  100  to effectuate an expanded state width W E  (not specifically identified in  FIGS. 7A and 7B  for ease of illustration) that is greater than the initial state width W I  ( FIG. 1 ). In some embodiments, the expansion unit  524  can include both of the length and width flanges  530 A,  530 B; in other embodiments, the expansion unit  524  includes only the length flange  530 A or only the width flange  530 B. 
     Apart from dimensions, each of the flanges  530  can have a similar construction. For example, each of the flanges  530  can be a lightweight yet relative stiff material. As identified in  FIG. 7B  for the width flange  530 B, each of the flanges  530  can define a fixed end  540  opposite a free end  542 . Further, a fold line  544  can be formed intermediate the ends  540 ,  542 . With this construction, the flange  530  can be viewed has having or defining a first portion  546  between the fixed end and the fold line  544 , and a second portion  548  between the fold line  544  and the free end  542 . The fixed end  540  can be connected to, or is configured for connection to be a user, the corresponding frame structure of the air filter unit  22  (e.g., the fixed end  540  of the width flange  530 B is connected to the side frame structure  100 ) in a manner permitting pivoting movement at the point or line of connection. For example, in some embodiments the flange  530  is a paperboard body integrally formed with the outer frame assembly  32 , with a fold line being formed at the line of interface between the flange  530  and the corresponding frame structure  100 ,  104  of the outer frame assembly  32  to define the fixed end  540  as described above. The fold line  544  arranges the first and second portions  546 ,  548  in differing spatial orientations. For example, with the non-limiting example of  FIGS. 7A and 7B , the second portion  548  extends over or overlaps the first portion  546 . Other spatial arrangements are also envisioned, and in other embodiments, two or more fold lines can be formed along the corresponding flange  530 . 
     With embodiments in which the air filter device  520  is provided to a user with the flange(s)  530  pre-assembled to (e.g., integrally formed with) the air filter unit  22  and pre-folded to arrangement shown in  FIGS. 7A and 7B , the user installs the air filter device  520  (including the flange(s)  530 ) to the air filter compartment (not shown). With embodiments in which the air filter device  520  is provided to a user with the flange(s)  530  either uncoupled from the air filter unit  22  or pre-assembled to the air filter unit  22  but not fully folded (e.g., the fold line  544  can be imparted into the flange  530 , but the second portion  548  is not completely folded relative to the first portion  546 ), the user can first compare an estimated size of the air filter compartment with the length and width L I , W I  dimensions of the air filter unit  22 . Based on this comparison, one or both of the flanges  530 A,  530 B can be mounted to the air filter unit  22  as described above and then folded at the corresponding fold line  544  (or, if pre-assembled but not yet folded, the selected flange(s)  530 A,  530 B can then be folded), with the so-configured air filter device  520  then being installed to the air filter compartment. In either instance, the air filter device  520  can be installed such that the fixed end  540  of the flange(s)  530  is opposite of the upstream direction of airflow through the air filter compartment. During operation of the air handling device, airflow (designated by arrow F in  FIG. 7A ) will interface between the flange(s)  530  and the outer frame assembly  32 , forcing the flange(s)  530  to extend outwardly relative to the outer frame assembly  32  (e.g., the flange(s)  530  is caused to pivot relative to the outer frame assembly  32  at the fixed end  540 , with the corresponding free end  542  moving outwardly away from the outer frame assembly  32 ). In this expanded state, the flange(s)  530  can be forced into contact with framework of the air filter compartment, promoting a seal between the air filter device  520  and the air filter compartment. The folded arrangement of the flange(s)  530  better ensures contact between the free end  542  (and other regions of the flange  530 ) and the air filter compartment framework. 
     Another air filter device  620  including an example expansion unit  624  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 8A and 8B . As a point of reference, the expansion unit  624  can be pre-assembled to the air filter unit  22  in a delivery condition of the air filter device  620 .  FIGS. 8A and 8B  reflect a possible expanded state of the air filter device  620 . 
     The expansion unit  624  includes at least one flange  630  that can be generally akin to the flanges  330  ( FIG. 5A ) described above. The flange  630  is generally sized and shaped in accordance with a designated region of the air filter unit  22 , such as dimensions of one of the end frame structures  104  or one of the side frame structures  100 . For example,  FIGS. 8A and 8B  illustrate the flange  630  as being associated with the end frame structure  104 . Alternatively, the flange  630  can be associated with one of the side frame structures  100 . In yet other embodiments, the expansion unit  624  can include two (or more of flanges  630 ), such as a flange at each of the side frame structures  100 , a flange at each of the end frame structures  104 , a first flange at one of the side frame structures  100  and a second flange at one of the end frame structures  104 , etc. 
     The flange  630  can include a main panel  640  and locking tabs  642 ,  644 . The main panel  640  is sized and shaped in accordance with dimensions of the corresponding frame structure  100 ,  104 . The locking tabs  642 ,  644  extend from opposing side edges of the main panel  640 . In other embodiments, a single one of the tabs  642  or  644  is included. The main panel  640  defines a fixed end  650  opposite a free end  652 . The fixed end  650  can be connected to, or is configured for connection to by a user, the corresponding frame structure of the air filter unit  22  (e.g., the fixed end  650  is connected to the end frame structure  104 ) in a manner permitting pivoting movement at the point or line of connection. The panel  640  projects away from the fixed end  650 , terminating at the free end  652  that is otherwise free of direct connection or attachment to the air filter unit  22 . For example, in some embodiments the flange  630  is a paperboard body integrally formed with the outer frame assembly  32 , with a fold line being formed at the line of interface between the main panel  640  and the corresponding frame structure  100 .  104  of the outer frame assembly  32  to define the fixed end  650 , and additional fold lines defining the locking tabs  642 ,  644  relative to the main panel  640 . 
     The locking tabs  642 ,  644  are configured to selectively lock the flange  630  relative to the air filter unit  22  at a desired spatial orientation. For example, each of the locking tabs  642 ,  644  can form or define a tab end  660  projecting from a shoulder  662  as identified for the locking tab  642  in  FIG. 8B . The tab end  660  is sized for insertion within one or more locking slots  664  formed in the outer frame assembly  32 . Upon insertion, the shoulder  662  bears against a structure of the outer frame assembly  32 , with this interface preventing the flange  630  from collapsing on to the outer frame assembly  32 . In some embodiments, a plurality of the locking slots  664  are provided, with the locking slots  664  being arranged in a spaced apart manner to provide differing spatial orientations of the flange  630  relative to the outer frame assembly  32 , and thus a range of available including spacings between the free end  652  and the outer frame assembly  32 . The locking slots  664  can be formed in various manners (e.g., slits, cuts, perforations, etc. through a thickness of the corresponding frame structure of the outer frame assembly  32 ), and may or may not be complete cuts in the initial state (e.g., to the extent a user desires to employ a selected one of the locking slots  664 , the selected locking slot  664  can first be “completed” by the user). Other locking mechanisms or techniques are also acceptable that may or may not entail the locking slots  664 ; for example, an adhesive can be provided along a face of the locking tabs  642 ,  644 . 
     Use of the air filter device  620  can include the first comparing an estimated size of the air filter compartment with the length and width L I , W I  ( FIG. 2A ) dimensions of the air filter unit  22  for which one of the flanges  630  is available (e.g., with the non-limiting example of  FIGS. 8A and 8B , the flange  630  is available to affect an expansion in the length direction). Based on this comparison, the flange  630  can be arranged to an expanded state corresponding with the estimated dimension by coupling the locking tabs  642 ,  644  to the outer frame assembly  32  at a desired location (e.g., the locking tabs  642 ,  644  are connected to the locking slot  664  appropriate for locating the free end  652  at a spatial position that effectuates an expanded length L E  corresponding with the estimated length of the air filter compartment). The so-configured air filter device  620  can then be installed to the air filter compartment, with the free end  652  contacting framework of the air filter compartment to promote a seal between the air filter device  620  and the framework. In other instances, the comparison may indicate that the air filter unit  22  is appropriately sized for installation to the air filter compartment, in which case the flange  630  is not transitioned to an expanded stated. Instead, the flange  630  can remain collapsed against the outer frame assembly  32  with installation of the air filter device  620  to the air filter compartment. 
     Another air filter device  720  including an example expansion unit  724  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 9A and 9B . As a point of reference, the expansion unit  724  can be pre-assembled to the air filter unit  22  in a delivery condition of the air filter device  720 . The expansion unit  724  can be configured to self-deploy to the expanded state reflected by  FIGS. 9A and 9B  in the presence of airflow as described below. 
     The expansion unit  724  includes first-fourth flanges  730 A- 730 D. The flanges  730 A- 730 D can be akin to the flanges  330  ( FIG. 5A ) described above, and are generally sized and shaped in accordance with a designated region of the air filter unit  22 . For example, the first and second flanges  730 A,  730 B are each generally sized and shaped in accordance with dimensions of one of the end frame structures  104  to effectuate an expanded state length L E  (not specifically identified in  FIGS. 9A and 9B  for ease of illustration) that is greater than the initial state length L I  ( FIG. 1 ). The third and fourth flanges  730 C,  730 D are each generally sized and shaped in accordance with dimensions of one of the side frame structures  100  to effectuate an expanded state width W E  (not specifically identified in  FIGS. 9A and 9B  for ease of illustration) that is greater than the initial state width W I  ( FIG. 1 ). 
     Apart from dimensions, each of the flanges  730 A- 730 D can have a similar construction. For example, each of the flanges  730 A- 730 D can be a lightweight yet relative stiff material defining a fixed end  740  opposite a free end  742  (identified in  FIG. 9B  for the third flange  730 C). The fixed end  340  can be connected to the corresponding frame structure of the air filter unit  22  (e.g., the fixed end  740  of the third flange  730 C is connected to the side frame structure  100 ) in a manner permitting pivoting movement at the point or line of connection. The free end  742  of each of the flanges  730 A- 730 D is free of direct connection or attachment to the air filter unit  22 . Finally, a continuous connection feature  744  (drawn generally in  FIGS. 9A and 9B ) is established or provided between orthogonally adjacent ones of the flanges  730 A- 730 D that permits pivoting movement of the corresponding flanges while maintaining a continuous obstruction to airflow. For example, the first flange  730 A and the third flange  730 C are orthogonal to one another, and are connected to one another at the connection feature  744 . The connection feature  744  is configured such that the flanges  730 A,  730 C can readily transition from a collapsed arrangement (not shown), in which the flanges  730 A,  730 C are collapsed on to the outer frame assembly  32 , to the expanded state shown. The connection feature  744  remains intact throughout this transition, presenting a continuous structure or obstruction to airflow. For example, the connection feature  744  can include the flanges  730 A,  730 C providing complimentary engagement features, such as a tab-and-slot type connection, that permits sliding movement of the flanges  730 A,  730 C relative to one another. Alternatively, a series of folds can be imparted into a material defining an interface between the flanges  730 A,  730 C (e.g., akin to origami). In yet other embodiments, a separate corner piece (not shown) can be assembled to the flanges  730 A,  730 C in defining the connection feature  744 . 
     In some embodiments the flanges  730 A- 730 D are each a paperboard body integrally formed with the outer frame assembly  32 , with a fold line being formed at the line of interface between each of the flanges  730 A- 730 D and the corresponding frame structure  100 ,  104  of the outer frame assembly  32  to define the fixed end  740 . 
     During use, the air filter device  720  can be installed such that the free end  742  of each of the flanges  730 A- 730 D faces the upstream direction of airflow through the air filter compartment. During operation of the air handling device, airflow (designated by arrow F in  FIG. 9A ) will interface between the flanges  730 A- 73 D and the outer frame assembly  32 , forcing the flanges  730 A- 730 D to extend outwardly relative to the outer frame assembly  32  (e.g., the flanges  730 A- 730 D are caused to pivot relative to the outer frame assembly  32  at the corresponding fixed end  740 , with the corresponding free end  742  moving outwardly away from the outer frame assembly  32 ). The expansion unit  724  can optionally be viewed as self-energizing to the expanded state. In the expanded state, the flanges  730 A- 730 D can be brought into contact with framework of the air filter compartment, promoting a seal between the air filter device  720  and the air filter compartment. 
     Another air filter device  820  including an example expansion unit  824  (referenced generally) in accordance with principles of the present disclosure applied to the air filter unit  22  is shown in  FIGS. 10A and 10B . As a point of reference,  FIGS. 10A and 10B  reflect a possible expanded state of the air filter device  820  in which the expansion unit  824  has been mounted to the air filter unit  22 . Conversely, a possible delivery condition (not shown) of the air filter device  820  includes the expansion unit  824  not yet mounted to the air filter unit  22  (e.g., a user can receive the air filter device  820  in the delivery condition, and then mount the expansion unit  824  (or portions thereof) to the air filter unit  22  in achieving the possible expanded state). 
     The expansion unit  824  includes one or more seal bodies  830 . The seal bodies  830  are generally sized and shaped in accordance with a designated region of the air filter unit  22 , and can include first-fourth seal bodies  830 A- 830 D. The first and second seal bodies  830 A,  830 B can each be generally sized and shaped in accordance with dimensions of one of the end frame structures  104  to effectuate an expanded state length L E  (not specifically identified in  FIGS. 10A and 10B  for ease of illustration) that is greater than the initial state length L I  ( FIG. 1 ). The third and fourth seal bodies  830 C,  830 D can each be generally sized and shaped in accordance with dimensions of one of the side frame structures  100  to effectuate an expanded state width W E  (not specifically identified in  FIGS. 10A and 10B  for ease of illustration) that is greater than the initial state width W I  ( FIG. 1 ). In other embodiments, the expansion unit  824  can include less than all of the first-fourth seal bodies  830 A- 830 D. 
     Apart from dimensions, each of the seal bodies  830  can have a similar construction. For example, each of the seal bodies  830  can be formed of a light weight, resilient, at least slightly compressible material capable of maintaining a designated shape when subjected to compression. In some embodiments, the seal bodies  830  can be a foam material (e.g., open or closed cell foams, natural foams, synthetic foams, etc.). In related embodiments, the seal bodies  830  can be hollow structures. Other materials, such as rubber, plastic, etc., are also envisioned. In some embodiments, the seal bodies  830  associated can each be a pre-cut, hollow foam strip, sized and shaped in accordance with geometries of the corresponding air filter unit  22  components (e.g., the first and second seal bodies  830 A,  830 B are both pre-cut to a size and shape corresponding with dimensions of one of the end frame structures  104 ; the third and fourth seal bodies  830 C,  830 D are pre-cut to a size and shape corresponding with dimensions of one of the side frame structures  100 ). 
     In some embodiments, the air filter device  820  is initially provided to a user with the seal bodies  830 A- 830 D mounted to the air filter unit  22  (e.g., via an adhesive or other fastener). In related embodiments, one or more of the seal bodies  830 A- 830 D are pre-assembled to the air filter unit  22  in a releasable fashion (e.g., a pressure sensitive adhesive) that permits a user to selectively remove one or more of the pre-applied seal bodies  830 A- 830 D. In yet other embodiments, the delivery condition of the air filter device  820  can include the seal bodies  830 A- 830 D apart from the air filter unit  22 . With these configurations, the expansion unit  824  can further include one or more strips of double-sided adhesive tape or other fastening devices (e.g., complimentary strips of hook-and-loop fasteners) that are employed by a user to secure the seal bodies  830 A- 830 C at the locations shown. Alternatively, the seal bodies  830 A- 830 D can be coated with an adhesive that is temporarily covered by a release liner, the air filter unit  22  can be coated with an adhesive at desired locations and that are temporarily covered by a release liner, etc. 
     With embodiments in which the air filter device  820  is provided to a user with the seal bodies  830 A- 830 D permanently assembled to the air filter unit  22 , the user installs the air filter device  820  to the air filter compartment (not shown). With embodiments in which the air filter device  820  is provided to a user with the seal bodies  830 A- 830 D uncoupled from the air filter unit  22  or with the seal bodies  830 A- 830 D removably pre-mounted to the air filter unit  22 , the user can first compare an estimated size of the air filter compartment with the length and width L I , W I  dimensions of the air filter unit  22 . Based on this comparison, one or more of the seal bodies  830 A- 830 D can be mounted to (or removed from) the air filter unit  22  as described above, with the so-configured air filter device  820  then being installed to the air filter compartment. With circumstances in which at least one of the seal bodies  830 A- 830 D is mounted to the air filter unit  22  upon installation, the seal body/bodies  830 A- 830 D can be brought into contact with framework of the air filter compartment, promoting a seal between the air filter device  820  and the air filter compartment. 
     Features or components of two or more of the expansion units  224 ,  324 ,  424 ,  524 ,  624 ,  724 ,  824  described above can be combined. For example, any of the expansion units described above can further include at least the depth standoffs  230 C ( FIG. 4A ). 
     Returning to  FIG. 1 , the air filter devices of the present disclosure are useful in a wide variety of air handling applications. In some embodiments, the air filter device can be configured for use with HVAC systems. With these and other embodiments, a user is afforded the ability to custom fit the air filter device  20  (via expansion in one or more of the length, width, and depth directions L, W, D) to an exact size of the air filter compartment provided with the user&#39;s actual HVAC system. In related embodiments, the air filter device  20  can be provided as a universal product, appropriate for use with a number of different HVAC systems that might otherwise have slightly different air filter compartment dimensions. By way of example, different HVAC system manufacturers may each specify to a user that a 16″×20″×4″ air filter should be used with their HVAC system, yet the actual air filter compartment is sized and shaped to provide a best fit with slightly different dimensions (e.g., 16″×19″×4″; 16″×21″×4″; 15″×20″×4″; 17″×20″×4″; 16″×20″×3.5″; 16″×20″×4.5″; etc.). With this in mind, the air filter device  20  of the present disclosure can be configured such that outer length, width and depth dimensions of the air filter unit  22  correspond with the smallest expected air filter compartment dimensions utilized by several different HVAC system manufacturers. Continuing with the above example, then, the air filter unit  20  can be configured to have outer dimensions of 15″×19″×3.5″, and promoted to potential users as being acceptable for use with any HVAC system requiring a 16″×20″×4″ air filter. Upon evaluating the size of the actual air filter compartment, the user can then, if necessary, effectively expand the 15″×19″×3.5″ air filter unit  22  in one or more of the length, width and depth directions L, W, D as described above, transitioning the air filter device  20  to an expanded state having dimensions corresponding with those of the actual air filter compartment. Similar benefits can be recognized in other, non-HVAC air filter applications, such as with room air purifier filters, window air filters, etc. 
     The air filter devices and related methods of use of the present disclosure provide a marked improvement over previous designs. By promoting simple, manual expansion in one or more of the length, width and depth directions, the air filter devices of the present disclosure afford a user the ability to achieve a “best fit” with the air handling device to which the air filter is installed. 
     Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure.