You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application of U.S. Provisional Patent Application No. 61/390,334 filed Oct. 6, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The subject matter disclosed herein generally relates to furnaces, and in particular to a furnace door latch assembly. 
         [0003]    Furnaces often include doors to provide access to internal components. Door latches are used to secure the door to the furnace cabinet, and allow for the door to be opened. Embodiments of the invention relate to improvements in furnace door latches. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    An embodiment is a latch assembly for securing a furnace door to a furnace casing, the latch assembly comprising: a latch for placement on an inside of the furnace door; a knob for placement through a hole in the furnace door, the knob snapped into the latch, the knob for placement on a front surface of the furnace door; a gasket for placement between the knob and the latch; and a cap secured at an end of the knob, wherein the latch, knob, and cap are keyed to allow assembly in only one orientation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0006]      FIG. 1  is a perspective, partial cross-sectional view of latches mounted to a furnace door; 
           [0007]      FIG. 2  is an exploded perspective view of a latch assembly; and 
           [0008]      FIG. 3  is a cross-sectional view of the latch assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    Latch assemblies according to embodiments of the invention are used to secure doors on a furnace. Referring to  FIG. 1 , access to compartments in furnace is available through doors  100  attached to casing  102 . In exemplary embodiments, two doors may be used, one to access an upper compartment housing the heat exchangers and one to access a lower compartment housing the controller  54  and blower  26 . A shown in  FIG. 1 , latch assemblies  200  secure door  100  to furnace casing  102 . As described in further detail herein, latch assemblies  200  can be rotated clockwise or counter-clockwise and include two latch tabs. This allows the latch assemblies  200  to be used in multiple orientations (e.g., top of door and bottom of door) so that only one latch design is needed and doors can be moved from a top location to a bottom location by reorienting the latch assemblies  200 . 
         [0010]      FIG. 2  is an exploded perspective view of a latch assembly  200 . Latch assembly  200  includes a cap  202 , knob  204 , gasket  206  and latch  208 . When assembled to door  100 , gasket  206 , knob  204  and cap  202  are positioned on a front side of door  100  and latch  208  is positioned on a backside of door  100 . Knob  204  has a cylindrical knob body  210  having a recess  212  at a first end for receiving cap  202 . Cap  202  includes resilient tabs  214  that snap into knob  204 . As described in further detail with reference to  FIG. 4 , cap  202  includes snap features that once engaged, will prevent the resilient tabs  214  from unsnapping from the knob  204 . Cap  202  provides a seal against air leakage through the knob  204 . 
         [0011]    Knob body  210  has an opening therethrough for receiving a plurality of spaced fingers  216  extending from the latch  208 . Fingers  216  have prongs  218  extending radially outwardly that are received over an interior lip defining recess  212  to snap fittingly secure the knob  204  and latch  208 . Shoulders  220  on an interior surface of knob body  210  abut against fingers  216 . The interference between shoulders  220  and fingers  216  causes rotation of knob  204  to rotate latch  208 . Knob body  210  also includes a plurality of extensions  222  that are received in pockets  224  ( FIG. 1 ) in the latch  208 , between respective fingers  216 . The interference between the extensions  222  and the pockets  224  causes rotation of knob  204  to rotate latch  208 . Gasket  206  provides an airtight seal between the knob  204  and the door  100 . 
         [0012]    Latch  208  includes a generally rectangular latch body  226 . Latch body  226  includes two arcuate, cam surfaces  227 . As the knob  204  and latch  208  are turned from an unlatched state to a latched state, one cam surface  227  rides on an edge of the casing  102  to move the door  100  in a vertical direction. Two semi-circular latch tabs  228  extend away from latch body  226  and have a latch tab surface  230  distanced from and parallel to the surface of the latch body  226 . As shown in  FIG. 1 , the latch tab surface  230  is positioned behind the furnace casing the pull the door  100  tight against the furnace casing  102  in the latched position. The latch tab surface  230  is chamfered to facilitate positioning of the latch tab  228  behind the casing as the latch  208  rotates. The edge of latch body  226  rests on an edge of casing  102  to position door  100  in the vertical direction. The latch body  226  has a flat detent  229  ( FIG. 3 ) on an edge thereof that rests on the edge of the casing  102  in the latched position. 
         [0013]    When the latch  200  is in a first orientation (e.g., latch tabs  228  aligned horizontally), door  100  can be mounted against casing  102  as latch body  226  clears the opening in casing  102 . As knob  204  is rotated (either clockwise or counter-clockwise), a cam surface  227  contacts an edge of the casing  102  to move the door in a vertical direction as knob  204  is rotated. Latch tab  228  moves behind casing  102  to pull door  100  against casing  102  with latch tab surface  230  in contact with casing  102 . As the latch  208  is rotated, this forces the door to be moved vertically while compressing casing insulation. Once the latch assembly  208  has rotated 90 degrees, detent  229  ( FIG. 3 ) on the edge of latch body  226  rests on an edge of casing  102 , locating the door vertically. 
         [0014]      FIG. 3  is a cross-sectional view of a latch assembly  200  mounted on door  100 . As shown in  FIG. 3 , the resilient tabs  214  have an edge  215  that is received under a lip  217  extending radially inwards from fingers  216 . In this construction, the resilient tabs  214  are secured to fingers  216  and prevent fingers  216  from being disengaged from knob  204  until cap  202  is removed. The cap  202  is keyed to the knob  204  (e.g., via a notch on the cap  202  and a tab on knob  204 , or vice versa) so that the cap  202  and knob  204  only mate in a single orientation. Further, the knob  204  and latch  208  are keyed, so that the knob  204  and latch  208  only mate in a single orientation  204  (e.g., via a notch on the knob  204  and a tab on latch  208 , or vice versa). Flat detent  229  is provided on the surface of latch body  226  to coincide with an edge of casing  102  once the latch assembly  200  has been rotated to the latched position. 
         [0015]    Embodiments of the invention attach furnace doors to a casing and provide a tight seal against either the top or bottom plate insulation and front edges of casing. Latches are rotatable and operate either clockwise or counter clockwise. The latches are air tight in their design, snap together, not easily come apart, and hold door secure over the operating life of the furnace. The snap together design allows door to be swapped between the top and bottom compartments and the latches can be oriented correctly. The latches provide a tight seal to restrict air flow into the combustion compartment, increasing burner reliability. 
         [0016]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Summary:
A latch assembly for securing a furnace door to a furnace casing, the latch assembly comprising: a latch for placement on an inside of the furnace door; a knob for placement through a hole in the furnace door, the knob snapped into the latch, the knob for placement on a front surface of the furnace door; a gasket for placement between the knob and the latch; and a cap secured at an end of the knob, wherein the latch, knob, and cap are keyed to allow assembly in only one orientation.