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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of U.S. Provisional Application No. 60/548,491 filed Feb. 27, 2004, which is entirely incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to installation of residential and light commercial HVAC equipment, and more particularly to suspension systems for air handlers, gas furnaces, and related HVAC equipment in attics and crawlspaces. 
   2. Discussion of the Related Art 
   Currently, residential and light commercial HVAC equipment, including air handlers and gas furnaces, are typically installed in attics and crawlspaces in the manner illustrated in  FIG. 1  (referred to herein as the “prior art manner of installation”).  FIG. 1  shows 22-gauge sheet metal strapping  10 , nailed to overhead wood trusses at the top and connected to a secondary pan  12  at the bottom. Near the bottom, a length of angle iron  14  is connected to the 22-gauge sheet metal strapping  10  to form a cradle upon which sits the HVAC unit  5 . Several shortcomings are inherent with the prior art manner of installation. 
   For example, the prior art manner of installation typically requires at least two people to carry out the installation. The prior art manner of installation requires the usage of heavy and relatively expensive angle iron  14 . The prior art manner of installation lacks adjustability, which makes it difficult to achieve the proper pitch (or levelness) of the HVAC unit  5 . The prior art manner of installation also makes it difficult to achieve the proper pitch for the secondary pan  12 . The prior art manner installation requires the 22-gauge strapping  10  to be cut to fit in the field, which leaves the 22-gauge strapping  10  with sharp corners and edges that can injure the installers, other trades people, the owner or anyone else in the area. The prior art manner of installation leaves the secondary pan  12  in a position that often gets bumped by other tradesmen and/or the owner, which can bend the secondary pan  12  and defeat the purpose of the secondary pan  12  by permitting leakage onto surfaces below. Similarly, the prior art manner of installation can permit leakage from the air handler  5  to travel along the length of the angle iron  14 , bypassing the secondary pan  12 , and drip on surfaces below. 
   Other hanging apparatus have been disclosed in the following United States or foreign patents: U.S. Pat. No. 77,587 (L H Colborn), U.S. Pat. No. 382,171 (G W Lutz), U.S. Pat. No. 528,319 (A J Beaton), U.S. Pat. No. 670,870 (J R Drozeski), U.S. Pat. No. 2,025,377 (C W Crannel), U.S. Pat. No. 2,057,092 (R L Geib), U.S. Pat. No. 3,355,030 (N E Cathcart), U.S. Pat. No. 3,907,118 (J Y Pelavin), U.S. Pat. No. GB 2,092,257 (J Harding), and U.S. Pat. No. 6,457,692 (W E Gohl, Jr.). None of these references, however, disclose the aspects of the current invention. 
   SUMMARY OF THE INVENTION 
   The invention is summarized below only for purposes of introducing embodiments of the invention. The ultimate scope of the invention is to be limited only to the claims that follow the specification. 
   Generally, the present invention (referred to also as the “suspension system”) is incorporated in a system for suspending an HVAC unit  5  from one or more top support members through the use of one or more top lock plates  22  connected to the top support member, one or more channels  23  connected to the HVAC unit  5 , one or more bottom lock plates  36  slidably coupled to the channels  23 , and one or more suspension chains  26  connected between the top lock plates  22  and the bottom lock plates  36 . The suspension system provides a system for suspending HVAC equipment for residential and light commercial applications that is safer, quicker, cheaper, more reliable and more accurate than systems currently in use. 
   For example, the suspension system allows most residential and light commercial HVAC equipment to be installed by one person. The suspension system does not require the usage of heavy and relatively expensive angle iron. As described in more detail below, the suspension system can be adjusted at least three times during and after installation: (1) gross adjustments can be made by adjusting the lengths of suspension chain  26  through the top and bottom lock plates  22 ,  36 , (2) fine adjustments can be made by rotating the top lock plate  22  about the first fastening point  32  before fixing the second fastening point  34 , and (3) fine adjustments can be made by sliding the bottom lock plate  36  along the channels  23 . The suspension system need not leave any sharp edges or sharp corners and edges that could injure the installers, other trades people or the owner. The suspension system permits the secondary pan  12  to be installed in close proximity to the HVAC unit  5  to minimize bumping or bending by other tradesmen and/or the owner. Similarly, the suspension system does not employ any angle iron  14 , so no leakage bypasses the secondary pan  12  to drip on surfaces below. 
   The description of the invention that follows, together with the accompanying drawings, should not be construed as limiting the invention to the example shown and described, because those skilled in the art to which this invention pertains will be able to devise other forms thereof within the ambit of the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a widely used prior art system for hanging air handlers. 
       FIG. 2A  illustrates an embodiment of the suspension system in a six-connection point embodiment. 
       FIG. 3  illustrates another embodiment of the suspension system. 
       FIG. 4  illustrates a preferred embodiment of a top locking plate. 
       FIG. 4A  illustrates an alternative view of a top locking plate. 
       FIG. 5  illustrates an embodiment of a bottom locking plate. 
       FIG. 5A  illustrates a view of a bottom locking plate slidably connected to a channel  23 . 
       FIG. 5B  illustrates a top view of a bottom locking plate slidably connected to a channel  23 . 
       FIG. 6  illustrates a side view of one connection. The top arrows illustrate how a top lock plate  22  can be rotated about a first connection point  32  for added adjustability before fixing a second connection point  34 . The bottom arrows illustrate how a bottom lock plate  36  can be moved relative to the channel  23  for added adjustability before fixing the second connection point  34 . 
       FIG. 7  illustrates the preferred embodiment for a heat pump auxiliary pan installation method and location. 
       FIG. 7A  illustrates the preferred embodiment for a furnace (with cooling coils) auxiliary pan installation method and location. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
   It is to be understood that the descriptions below are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the detail of construction or design herein shown other than as defined in the appended claims. In this specification, the term “HVAC unit” refers to any heating, venting or air conditioning unit, including a gas furnace, a heat pump air handler or other similar residential or light commercial HVAC equipment. Examples of an “HVAC unit” include those units manufactured by the CARRIER® Corporation under model numbers 58STA, 58DLA, 58CTA, 58CVA, 58STX, 58DLX, 58CTX, and 58CVX, those manufactured by GOODMAN® Manufacturing Company, L.P., those manufactured by American Standard, Inc. under the trademark TRANE® and those manufactured by YORK® International Corporation. Other air handlers, furnaces and related HVAC equipment could also be employed by the suspension system described herein. Similarly, while the description that follows is generally directed at installations where a wood truss provides the structural support at the top, the suspension system described herein could be adapted to fit other types of structural top support members. 
   Generally, the invention is incorporated in a system for suspending an HVAC unit  5  from one or more wood truss members through the use of one or more top lock plates  22  connected to the wood truss, one or more channels  23  connected to the HVAC unit  5 , one or more bottom lock plates  36  slidably coupled to the channels  23 , and one or more suspension chains  26  connected between the top lock plates  22  and the bottom lock plates  36 . 
   While many materials, dimensions, thicknesses and combinations thereof can be used to construct the top lock plate  22 , it is preferred that the top lock plate  22  be made from 16 gauge galvanized steel. See e.g.,  FIG. 4A . The preferred top lock plate  22  is 6.6 inches long and 1.5 inches wide. The preferred top lock plate  22  has rounded corners and edges. The preferred top lock plate  22  has a first fastening point  32  located 0.75 inches from the top edge. The preferred top lock plate  22  has a second fastening point  34  located 1.5 inches below the first fastening point  32 . It is preferred that the first and second fastening points  32 ,  34  be a hole approximately 0.188 inch in diameter through the top lock plate  22 . 
   As shown in  FIG. 4 , the preferred top lock plate  22  has an opening to permit a suspension chain  26  to slidably pass through. While it is preferred to use a 1-inch 155-pound double loop chain for the suspension chain  26 , many types of chains, ropes, or other flexible tensile elements could be used. If the preferred chain is used, it is also preferred that the opening be 0.625 inches in diameter centered 1.8125 above the bottom of the top lock plate  22 . As shown in  FIG. 4 , it is preferred that a locking slot extend downward from the edge of the opening. The slot should be wide enough so that one link of chain can slide sideways into the slot, but not so wide to permit the suspension chain  26  to pass through the slot altogether. If the preferred suspension chain  26  is used, it is preferred that the slot be 0.141 inches wide and 1.3125 inches long. If the preferred top lock plate  22  is used, it is also preferred to use at least one lock plate for every 55 pounds of HVAC unit  5  being suspended. If the preferred suspension chain  26  is used, it is also preferred to use at least one suspension chain  26  for every 55 pounds of HVAC unit  5  being suspended. 
   Like the top lock plate  22 , many materials, dimensions, thicknesses and combinations thereof can be used to construct the channels  23 . It is preferred that the channels  23  be made from 16 gauge galvanized steel. The preferred channels  23  are connected to the top side of the HVAC unit  5  with a fastening means. Many types of fasteners  30  can be used. It is preferred to use #8 hex screws. It is recommend that prior to connecting the bottom lock plate  36  to the cabinet of the HVAC unit  5 , the installer should verify that the fastener  30  will not interfere with the interior wiring or other internal HVAC parts upon during the connection process. The preferred channels  23  have a plurality of fastening points spaced evenly along the length of the HVAC unit  5  as shown in  FIG. 5B . The channels  23  should have rounded corners and edges. 
   Like the top lock plate  22 , many materials, dimensions, thicknesses and combinations thereof can be used to construct the bottom lock plate  36 . It is preferred that the bottom lock plate  36  be made from 16 gauge galvanized steel. The preferred bottom lock plate  36  is 16 inches long and 1.5 inches wide. The preferred bottom lock plate  36  has rounded corners and edges. The preferred bottom lock plate  36  has a pair of notches  28  as shown in  FIGS. 5 &amp; 5A . The preferred bottom lock plate  36  also has a 90 degree bend. The 90 degree bend should occur at a distance below the notches to permit the bottom lock plate  36  to slide but not twist within the channel  23  as shown in  FIG. 5A . 
   As shown in  FIG. 5 , the preferred bottom lock plate  36  has an opening to permit a suspension chain  26  to slidably pass through. While it is preferred to use a 1-inch 155-pound double loop chain for the suspension chain  26 , many types of chains, ropes, or other flexible tensile elements could be used. If the preferred suspension chain is used, it is also preferred that the opening be 0.625 inches in diameter centered 1.8125 below the top of the bottom lock plate  36 . As shown in  FIG. 5 , it is preferred that a locking slot extends upward from the edge of the opening. The slot should be wide enough so that one link of chain can slide sideways into the slot, but not so wide to permit the suspension chain  26  to pass through the slot altogether. If the preferred suspension chain  26  is used, it is preferred that the slot be 0.141 inches wide and 1.3125 inches long. If the preferred bottom lock plate  36  is used, it is also preferred to use at least one bottom lock plate  36  for every 55 pounds of HVAC unit  5  being suspended. 
   While many fasteners  30  can be used to connect the top locking plate to the wood truss, it is preferred to connect the top lock plate  22  to the wood truss using 16d nails. During installation, it is preferred that only the first fastening point  32  be connected to the truss at the beginning. Once the HVAC unit  5  has been hung and the suspension chains  26  adjusted, the top lock plate  22  can be rotated about the first fastening point  32  to make finer adjustments to the level height of the HVAC unit  5  before the second fastening point  34  is connected to the wood truss. As such, it is preferred to size the fastener and top lock plate  22  so that the connection at the first fastening point can support the entire design load. This permits the rotational adjustability before fastening the second fastening point  34 . Of course, the order of connecting the fasteners could be reversed (i.e., fasten the second fastening point  34  first, rotate about the second fastening point  34  for adjustability and then fasten the first fastening point  32 .) 
   Once the HVAC unit  5  has been suspended, a secondary pan  12  can be fastened directly to the cabinet of the HVAC unit  5 . It is preferred to fasten the secondary pan  12  using #8 hex screws. The secondary pan  12  should be adjusted to create a slight tilt towards the corner nearest the drain  38 . The secondary pan  12  is preferably installed less than one inch clearance below the bottom of the HVAC unit  5 . The secondary pan  12  is preferably sized so that it does not extend past the ends of the unit. 
   As shown in  FIG. 7 , it is preferred to strap the secondary pan  12  in a location so that the secondary pan  12  covers the area underneath the entire coil for the heat pump. As shown in  FIG. 7A , it is preferred to strap  40  the secondary pan  12  in a location so that the secondary pan  12  covers the area underneath the entire coil and supply plenum for the furnace. Most any straps  40  can be used, but it is preferred to use sheet metal straps with ½-inch long, #8 metal screws in the locations shown. Other fastening methods, including those approved by Byan, can also be employed. 
   In pratice, an installer using the preferred embodiments of the suspension system described herein could employ the following steps to install an HVAC unit  5  in a residential or light commercial application having wood trusses for support:
         1. Set HVAC unit  5  on surface below the location where the HVAC unit  5  is intended to be suspended;   2. Connect channels  23  to HVAC unit  5  as shown in  FIGS. 2-6 , using at least 4-#8 hex screws per channel  23 , and verifying that no screw will interfere with heating coil, wiring or other HVAC unit  5  parts as it penetrates cabinet wall;   3. Slide bottom lock plates  36  into the channels  23  as shown in  FIG. 5A .   4. Connect the top lock plate  22  to the top chord of truss by driving one 16 d nail through the first fastening point  32 , making sure top lock plates  22  are plumb with the straps on the equipment and in-line with each other;   5. Cut the suspension chain  26  to length by applying the following formula:
 
Length of suspension chain= A−B  plus 10 inches, where
           A=the distance from the locking slot in the top lock plate  22  to the locking slot on the bottom lock plate  36  when the HVAC unit  5  sitting on the surface below the top supporting member with the bottom locking plates directly below the top locking plates.   B=the distance that the HVAC unit  5  will be suspended above the bottom surface (preferably at 24″ above surface if space allows).   
           6. Slip each suspension chain  26  through the opening of each top lock plate  22 , leaving three extra links of suspension chain  26  on one side of the top lock plate  22 ;   7. Lift one end of the HVAC unit  5  and slip the suspension chain  26  through the opening in each bottom lock plate  36 , leaving three extra links of suspension chain  26 ;   8. Lift other end and slip each remaining suspension chain  26  through the opening in each bottom lock plate  36 , leaving three extra links of suspension chain  26 ;   9. Adjust bottom lock plates within each channel as needed for minor leveling adjustments and/or to adjust the suspension chain  26  for desired plumbness;   10. Adjust links through locking slots in either the top or bottom lock plates to make HVAC unit  5  as close to level as possible;   11. Pivot top lock plates  22  about the first fastening point  32  to make final level adjustments to the HVAC unit  5 , and drive a second 16d nail through the second fastening point  34  once final adjustments have put the HVAC unit  5  in its most desired position;   12. Cut off any suspension chain  26  in excess of three extra links;   13. Connect secondary pan  12  to HVAC unit  5  with #8 hex screw, ensuring that secondary pan  12  is tilted towards the drain corner.       

   Although the invention has been described in detail with reference to one or more particular preferred embodiments, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the claims that follow.

Summary:
A system for suspending an HVAC unit from one or more wood truss members through the use of one or more top lock plates connected to a top support member, one or more channels connected to the top of the HVAC unit, one or more bottom lock plates slidably connected to the one or more channels, and one or more suspension chains connected between the top lock plates and the bottom lock plates to adjustably suspend the HVAC unit at the desired height and pitch. The suspension system provides a system for suspending HVAC equipment in residential and light commercial applications that is safer, quicker, cheaper, more reliable and more accurate than systems currently in use.