Abstract:
A hybrid wood-burning fireplace assembly configured for burning wood-based fuel, wherein the burning generates combustion exhaust. The assembly comprising a fire box having an interior area, a baffle in the interior area defining lower and upper combustion chambers relative to the baffle. The upper combustion chamber has an upper exhaust passageway between baffle and the top portion of the firebox. A secondary combustion airway has air outlets in the firebox that direct the secondary combustion air adjacent to the baffle to mix with the exhaust for non-catalytic secondary combustion of the exhaust before the exhaust flows through the upper exhaust passageway. A catalytic combustion unit is positioned above the baffle and across the upper exhaust passageway, whereby the exhaust will pass through the catalytic combustion unit after the non-catalytic secondary combustion of the exhaust and before the exhaust exits the upper combustion chamber through the upper exhaust passageway.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/029,740, titled HYBRID WOOD BURNING FIREPLACE ASSEMBLY and filed Sep. 17, 2013, which is a continuation of U.S. patent application Ser. No. 13/047,714, titled HYBRID WOOD BURNING FIREPLACE ASSEMBLY and filed Mar. 14, 2011, which is a non-provisional patent application that claims priority to and claims the benefit of U.S. Provisional Patent Application No. 61/313,678, title HYBRID WOOD BURNING FIREPLACE ASSEMBLY and filed Mar. 12, 2010, the disclosure of which is incorporated by reference in its entirety by reference thereto. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to fireplace assemblies, and more particularly to wood burning fireplace assemblies, including fireplace units, fireplace inserts and stoves and associated methods. 
       BACKGROUND 
       [0003]    Conventional fireplace assemblies are configured to burn a selected fuel, such as wood, pellets, gas, etc., and this burning of the fuel results in exhaust that contains combustion bi-products. As an example, a wood burning fireplace assembly, such as a stove or insert, is used to burn wood in the firebox, which creates combustion bi-products (solid and gaseous) that exit the firebox as exhaust. Technology has been developed to reduce or otherwise control the emissions from the fireplace assemblies, including catalytic fireplace assemblies and non-catalytic fireplace assemblies that provide for secondary combustion of the exhaust to reduce the emissions. 
         [0004]    Conventional catalytic fireplace assemblies having catalytic converters are generally effective in achieving low particulate emissions at low temperatures, but become less effective as temperatures rise. On the other hand, conventional non-catalytic fireplace assemblies having secondary combustion tubes are generally effective in causing secondary combustion of the combustion bi-products to achieve low particulate emissions at high temperatures, but become less effective as temperatures fall. In both cases, a bypass damper may need to be frequently controlled and/or other manual adjustments may need to be made in order to regulate the rate of combustion within the fireplace assembly. 
       SUMMARY 
       [0005]    The present invention provides a fireplace assembly that overcomes drawbacks experienced in the prior art and that provide other embodiments. At least one embodiment of the invention provides a hybrid fireplace assembly, including a fireplace unit, a stove or an insert, that comprises a fire box with an interior area configured to contain a combustible fuel that will burn and generate exhaust. The firebox has a front wall, a back wall, sidewalls, a base plate, a top portion, and an exhaust outlet. A baffle is connected to the firebox and disposed in the interior area to define a lower combustion chamber below the baffle and an upper combustion chamber above the baffle. The lower combustion chamber is sized and shaped to contain at least a portion of the fire from burning combustible fuel. The upper combustion chamber has an upper exhaust passageway between baffle and the top portion of the firebox. A primary combustion air passageway configured to carry primary combustion air to the lower combustion chamber. The primary combustion air passageway having an inlet that receives air therein for primary combustion and having at least one outlet in the firebox that directs primary combustion air toward the fire in the lower combustion chamber. A secondary combustion air passageway is configured to carry secondary combustion air into the firebox. The secondary combustion air passageway has an inlet that receives air therein for secondary combustion of at least portions of exhaust from the burning of the combustible fuel in the lower combustion chamber. The secondary combustion air passageway has air outlets in the firebox that directs the secondary combustion air adjacent to the baffle to mix with the exhaust for non-catalytic secondary combustion of the exhaust before the exhaust flows through the upper exhaust passageway. A catalytic combustion unit is positioned above the baffle and across the upper exhaust passageway whereby the exhaust will pass through the catalytic combustion unit after the non-catalytic secondary combustion of the exhaust and before the exhaust exits the upper combustion chamber through the upper exhaust passageway. The catalytic combustion unit is configured to remove combustion byproducts from the exhaust when the exhaust passes through the catalytic combustion unit. 
         [0006]    In one embodiment the secondary combustion air passageway is configured to facilitate the combustion of exhaust particles in a first range of temperatures with a first level of efficiency. The catalytic combustion unit is configured to provide combustion of exhaust particles in the first range of temperatures with a second level of efficiency less than the first level of efficiency. The secondary combustion air passageway facilitates the combustion of exhaust particles in a second range of temperatures greater than with a third level of efficiency, and the catalytic combustion unit is configured to provide combustion of exhaust particles in the range of second temperatures with a fourth level of efficiency greater than the third level of efficiency. 
         [0007]    Another aspect of an embodiment provides a hybrid wood-burning fireplace assembly configured for burning wood-based fuel, wherein the burning generates combustion exhaust. The assembly comprising a fire box having an interior area, a base portion, and a top portion with an exhaust outlet. A baffle is in the interior area defining a lower combustion chamber below the baffle and an upper combustion chamber above the baffle. The upper combustion chamber has an upper exhaust passageway between baffle and the top portion of the firebox. A primary combustion airway has an inlet that receives primary combustion air therein and has at least one outlet in the firebox that directs the primary combustion air to the lower combustion chamber for primary combustion with the burning wood-based fuel. A secondary combustion airway has an inlet that receives air therein for secondary combustion of at least portions of exhaust from the burning wood-based fuel in the lower combustion chamber. The secondary combustion airway has air outlets in the firebox that directs the secondary combustion air adjacent to the baffle to mix with the exhaust for non-catalytic secondary combustion of the exhaust before the exhaust flows through the upper exhaust passageway. A catalytic combustion unit positioned above the baffle and across the upper exhaust passageway whereby the exhaust will pass through the catalytic combustion unit after the non-catalytic secondary combustion of the exhaust and before the exhaust exits the upper combustion chamber through the upper exhaust passageway. 
         [0008]    Another aspect provides a method of reducing emissions from a wood-based fuel burning fireplace assembly. The method comprises burning a wood-based fuel in firebox of the fireplace assembly during primary combustion of the fuel to generate exhaust with particulates therein. The fireplace assembly has a baffle in the firebox that divides an interior area into an upper combustion chamber and a lower combustion chamber. The upper combustion chamber has an upper exhaust passageway between baffle and a top portion of the firebox. The method includes directing secondary combustion air into the lower chamber below the baffle for mixing with the exhaust for secondary combustion of the exhaust in the firebox, burning particulates in the exhaust in the secondary combustion adjacent to the baffle, and passing the exhaust after the secondary combustion through a catalytic combustion unit positioned across an exhaust passageway in the upper combustion chamber above the baffle, wherein passing the exhaust through the catalytic combustion unit removed additional particulates from the exhaust after the secondary combustion. The method can also include directing the exhaust out of the firebox after the exhaust exits the catalytic combustion unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an isometric view of a hybrid wood burning fireplace assembly in accordance with an embodiment of the present invention. 
           [0010]      FIG. 2  is an enlarged front isometric view of the hybrid fireplace assembly of  FIG. 1  showing a hybrid combustion system. 
           [0011]      FIG. 3  is an enlarged partial front isometric view of the hybrid fireplace assembly of  FIG. 1  showing the secondary combustion tubes in the firebox of the assembly. 
           [0012]      FIG. 4  is an enlarged, partial isometric view of the catalytic converter of the hybrid combustion system of  FIG. 2 . 
           [0013]      FIG. 5  is an enlarged, partial top isometric view of the fireplace assembly of  FIG. 1  showing a portion of the catalytic converter and a bypass damper visible through an exhaust aperture when the exhaust flue is removed. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    A hybrid fireplace assembly is described in detail herein in accordance with embodiments and aspects of the present invention. In one embodiment, a hybrid wood-burning fireplace assembly includes a hybrid combustion system having both catalytic and non-catalytic components. A non-catalytic component comprises one or more secondary combustion tubes that remove particulate emissions, such as carbon monoxide, from the exhaust gases generated by a wood burning fire. A catalytic component comprises a catalytic converter that removes additional particulate emissions from the exhaust gases before the gases are emitted from the fireplace assembly. Among other benefits, the hybrid fireplace assembly described herein improves heating efficiency and achieves low particulate emissions over a wide range of temperatures. 
         [0015]    The hybrid fireplace assembly described herein employs both a catalytic converter and secondary combustion tubes. At higher temperatures, the secondary combustion tubes are more effective at reducing particulate emissions, and the catalytic converter is used relatively less. At lower temperatures, the secondary combustion tubes are less effective at reducing particulate emissions, and the catalytic converter is used relatively more. The hybrid fireplace assembly provides a user-friendly, self-regulating system that accommodates temperature changes, without requiring excessive control of a bypass damper, opening and closing a door of the fireplace assembly, and/or making other manual adjustments. 
         [0016]    The fireplace assembly described herein may be used in combination with wood burning fireplaces, stoves, and fireplace inserts. In the following description, numerous specific details are discussed to provide a thorough and enabling description for embodiments of the disclosure. One skilled in the relevant art, however, will recognize that the disclosure can be practiced without one or more of the specific details. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosure. In general, alternatives and alternate embodiments described herein are substantially similar to the previously described embodiments, and common elements are identified by the same reference numbers. 
         [0017]      FIG. 1  is a front isometric view of a hybrid fireplace assembly  100  in accordance with an embodiment of the present invention. The hybrid fireplace assembly  100  includes a firebox  105  for containing a wood burning fire. The firebox  105  comprises a front wall  110 , a back wall  115 , a base plate  120 , a top plate  125 , and sidewalls  130 . 
         [0018]    The front wall  110  of the firebox  105  includes an opening  135  for receiving wood. The opening  135  receives a door  140  mounted by hinges  145  (identified individually as a first hinge  145   a  and a second hinge  145   b ) coupled to the front wall  110 . The door  140  has a glass window  150  or the like that allows the interior of the firebox  105  to be observed while the door is closed. A door seal  155  extending about the inside of the door  140  engages with the front panel  110  to provide an airtight seal when the door is closed. The door  140  also includes a handle  160  that can be rotated to latch and unlatch the door. 
         [0019]    In the illustrated embodiment, the hybrid fireplace assembly  100  also includes a flue adapter  165  configured to receive a direct vent chimney. The flue adapter  165  can be located on the top, back, or side of the hybrid fireplace assembly  100 . In an alternative embodiment, the hybrid fireplace assembly  100  includes two separate, non-concentric flues (e.g., an exhaust flue and an air intake flue) connected to the top, back, or side of the assembly. 
         [0020]    When the hybrid fireplace assembly  100  is operated, wood is placed within the firebox  105  adjacent to the base plate  120  and ignited in a usual manner. As the fire burns, it produces exhaust gases that contain particulate emissions, such as carbon monoxide, unburned hydrocarbons, and/or other gases that may be undesirable, such as for the environment. The exhaust gases are processed by a hybrid combustion system that includes a series of combustion stages—primary, secondary, tertiary, and catalytic. At each stage of combustion, particulate emissions are removed from the exhaust gases, so that by the time the exhaust gases reach the flue adapter  165 , most of the particulate emissions have been eliminated. This improved combustion of the wood fuel and the particulate emissions results in more heat produced by the same amount of wood. 
         [0021]      FIG. 2  is an enlarged front isometric view of the hybrid fireplace assembly  100  of  FIG. 1  showing a hybrid combustion system. The firebox  105  includes a baffle  205  extending between the sidewalls  130  from the back wall  115  toward the front wall  110 , and terminating in a leading edge  220  before it reaches the front wall  110 . The baffle  205  separates the firebox into a lower combustion chamber  210  between the baffle and the base plate  120 , and an upper combustion chamber  215  between the baffle and the top plate  125 . In the illustrated embodiment, the baffle is configured so the leading edge  220  is spaced apart from the front wall to provide an exhaust/air flow path from under the baffle, up and around the leading edge between the baffle and the front wall  110  to above the baffle  205 . In other embodiments, the baffle can be configured in another position or arrangement, such as to provide the leading edge adjacent to and spaced apart from, as an example, the rear wall or a side wall, so that the exhaust/air flow path is between the baffle&#39;s leading edge and the adjacent, spaced apart rear wall or side wall. 
         [0022]    The upper combustion chamber  215  includes a catalytic component of the hybrid combustion system—a catalytic converter  245 . The lower combustion chamber  210  includes a non-catalytic component of the hybrid combustion system—one or more secondary combustion air passageways, such as secondary combustion air tubes  230  affixed to the underside of the baffle  205 . 
         [0023]    In the illustrated embodiment, the baffle  205  comprises a metal plate having a top insulation layer. The insulation layer can comprise firebricks, ceramic fiber, vermiculite board, or the like. In other embodiments, the baffle  205  comprises one or more firebricks mounted on brackets. The insulated baffle  205  retains heat in the lower combustion chamber  210  below the baffle, in order to facilitate combustion at the secondary combustion tubes  230 . 
         [0024]    The location and thickness of the baffle  205  are determined based at least in part on the space needed above the baffle for the catalytic converter  245 . For example, the size of the hybrid fireplace assembly  100  can affect a minimum size and/or surface area needed for optimum performance of the catalytic converter  245 . A small hybrid fireplace assembly  100 , which generates relatively fewer particulate emissions, may require a relatively small catalytic converter  245 . Accordingly, the baffle  205  may be positioned relatively closer to the top plate  125 , and/or the baffle may be relatively thicker. A large hybrid fireplace assembly  100 , which generates relatively more particulate emissions, may require a relatively large catalytic converter  245 . Accordingly, the baffle  205  may be positioned relatively further away from the top plate  125 , and/or the baffle may be relatively thinner. 
         [0025]    In some embodiments, the baffle  205  is substantially horizontal and parallel with the base plate  120 . In other embodiments, the baffle  205  is sloped, such as upward from the rear wall  115  toward the front wall  110 , such that the leading edge  220  of the baffle is higher than a rear edge of the baffle that intersects with the rear wall. The degree of slope is determined based at least in part on the size of the firebox  105 . For example, a relatively large firebox  105  can generally accommodate a sloped baffle  205 , while a relatively small firebox may be better suited for a horizontal baffle. The slope of the baffle  205  (or lack thereof) can affect the speed of the flow of a secondary air supply along the underside of the baffle, described in additional detail herein. A horizontal baffle  205  (i.e., with zero or approximately zero degree slope) can cause the secondary air supply to flow at a relatively slow rate. As the degree of slope of the baffle  205  increases, the secondary air supply is directed increasingly upward, and thus flows at a relatively faster rate. 
         [0026]    Primary and secondary combustion occur in the lower combustion chamber  210  of the firebox  105 . Primary combustion occurs adjacent to the base plate  120 , as the burning wood comes into contact with a primary air supply and generates exhaust gases. The primary air supply can be distributed into the firebox  105  from a variety of locations, such as a primary air intake aperture  225  (identified individually as first primary air intake aperture  225   a  and second primary air intake aperture  225   b ) located in the base plate  120 . The primary air intake aperture(s)  225  are fluidly coupled to a base chamber  170  on the underside of the base plate  120  that freely provides the primary air supply to the aperture(s). The primary air supply mixes with the exhaust gases adjacent to the base plate  120  and upstream of the secondary combustion tubes  230 , removing particulate emissions from the exhaust gases. 
         [0027]    In some embodiments, the primary air supply is spaced apart from the firebox  105 , such that the primary air supply is not heated substantially by the firebox prior to entry via the primary air intake aperture(s)  225 . For example, the base chamber  170  may be located apart from the firebox  105 , and/or an insulation layer between the firebox and the base chamber may reduce the flow of heat from the firebox to the base chamber. Such an arrangement enables delivery of a maximum concentration of oxygen (O 2 ) to the base plate  120  for primary combustion. 
         [0028]    In some embodiments, a primary air control (not shown) is provided to allow a user to selectively control the flow of the primary air supply. The primary air control can extend along the underside of the firebox  105  through a control opening  250  (identified individually as a first control opening  250   a  and a second control opening  250   b ). The primary air control can be opened completely to allow for free flow of the primary air supply through the primary air intake aperture(s)  225 , or the primary air control can be progressively closed to reduce the flow of the primary air supply through the primary air intake aperture(s). 
         [0029]    Secondary combustion also occurs in the lower combustion chamber  210 . Secondary combustion occurs adjacent to one or more secondary combustion tubes  230  that carry a secondary air supply.  FIG. 3  is an enlarged front isometric view of the hybrid fireplace assembly  100  of  FIG. 1  showing the secondary combustion tubes  230 . In the illustrated embodiment, the hybrid fireplace assembly  100  includes four secondary combustion tubes  230 ,  320 ,  325 , and  330 . The number, size, and position of the secondary combustion tubes  230 ,  320 ,  325 , and  330  can vary based on, as an example, the size of the firebox  105 , the desired oxygen (O 2 ) level for mixture with the exhaust gases, and/or a variety of other factors. 
         [0030]    The secondary combustion tubes  230 ,  320 ,  325 , and  330  are mounted to common side chambers  305  (only one side chamber shown) by fasteners  310  (only one fastener shown). The side chambers  305  receive the open ends of the secondary combustion tubes  230 ,  320 ,  325 , and  330 , as illustrated by the broken line  315 . The side chambers  305  are fluidly coupled to a secondary air supply, and freely provide this secondary air supply to the secondary combustion tubes  230 ,  320 ,  325 , and  330 . In some embodiments, the secondary air supply is warmed to within a particular temperature range in order to facilitate more efficient secondary combustion. 
         [0031]    Each of the secondary combustion tubes  230  includes a plurality of air distribution holes  235  along the length of the tube that distribute the secondary air supply into the firebox  105 . In some embodiments, the air distribution holes  235  are oriented at a selected angle relative to the baffle, such as substantially parallel or horizontally. The air distribution holes  235  direct the secondary air supply into the firebox  105  toward the leading edge  220  of the baffle  205 . Such an arrangement of air distribution holes  235  helps to reduce or avoid turbulence between the secondary air supply and the burning fire, and allows the secondary air supply to blend with the flow of exhaust gases passing forwardly under the baffle  205 , while maintaining an active flame in the firebox  105 . 
         [0032]    In the illustrated embodiment, each of the secondary combustion tubes  230 ,  320 ,  325 , and  330  has air distribution holes  235  that are similarly spaced, sized, and oriented. In other embodiments, each of the secondary combustion tubes  230 ,  320 ,  325 , and  330  has air distribution holes  235  that are differently spaced, sized, and/or oriented. The spacing, size, and/or orientation of the air distribution holes  235  can be based on the size of the firebox, the desired oxygen (O 2 ) level for mixture with the exhaust gases, and/or a variety of other factors. In the illustrated embodiments, the air distribution holes are shown below the baffle. In other embodiments, one or more secondary combustion tube  230  can be positioned, configured, or oriented to that a plurality of the air distribution holes are positioned above a portion of the baffle, e.g., above the leading edge area of the baffle, but still upstream of the catalytic converter discussed above. This arrangement can provide for an air flow above the baffle that mixes with the exhaust gases before passing through the catalytic converter. 
         [0033]    As the secondary air supply is distributed into the firebox  105  by the air distribution holes  235 , the secondary air supply mixes with the exhaust gases downstream of primary combustion and upstream of the leading edge  220  of the baffle  205 , removing additional particulate emissions from the exhaust gases. The secondary combustion tubes  230 ,  320 ,  325 , and  330  are more effective at reducing particulate emissions at higher temperatures. Accordingly, fewer particulate emissions remain to be removed during the tertiary and catalytic combustion stages, described herein. At lower temperatures, the secondary combustion tubes  230 ,  320 ,  325 , and  330  are less effective at reducing particulate emissions. Accordingly, more particulate emissions remain to be removed during the tertiary and catalytic combustion stages. 
         [0034]    Conventional secondary combustion tubes used by existing non-catalytic fireplace assemblies are not used in the hybrid wood burning fireplace assembly  100  described herein. For example, to obtain a desired level of particulate emissions at high temperatures, secondary combustion tubes with a conventional size, orientation, hole distribution, etc., generate a high level of excess air. If these conventional secondary combustion tubes were to be combined with a catalytic converter, the conventional tubes would provide an excessive flow of air (including too much oxygen) around the baffle and through the catalytic converter, resulting in ineffective use of the catalytic converter. Accordingly, the secondary combustion tubes in the hybrid wood burning fireplace assembly  100  described herein must be configured with a desired size, spacing, and/or orientation of the air distribution holes of the tubes, based at least in part upon the configuration of the firebox, the catalytic converter, and other factors. 
         [0035]    In some embodiments, secondary combustion includes a rear air supply in addition to the secondary air supply. In the illustrated embodiment, a back wall chamber  340  mounted to the back wall  115  is fluidly coupled to a rear air supply. The back wall chamber  340  includes a plurality of rear air distribution holes  335 . Like the air distribution holes  235  of the secondary combustion tubes  230 , the rear air distribution holes  335  in the illustrated embodiment are spaced substantially horizontally, such that they direct a rear air supply into the firebox  105  toward the leading edge of the baffle  205 . This arrangement of rear air distribution holes  335  helps to reduce or avoid turbulence between the rear air supply and the burning fire, allowing the rear air supply to blend with the flow of exhaust gases passing forwardly under the baffle  205 , while maintaining an active flame in the firebox  105 . 
         [0036]    Like the air distribution holes  235  of the secondary combustion tubes  230 , the rear air distribution holes  335  can be evenly spaced across the surface of the back wall chamber  340 . In other embodiments, including the illustrated embodiment, the rear air distribution holes  335  are variably spaced across the surface of the back wall chamber  340 . Such variations in the placement of the rear air distribution holes  340  can be based on the size of the firebox, the desired oxygen (O 2 ) level for mixture with the exhaust gases, and/or a variety of other factors. Alternatively or additionally, variations can be made in the size and orientation of the rear distribution air holes  340  based on similar factors. 
         [0037]    The presence or absence of a back wall chamber  340  can be determined based on the size of the firebox, the desired oxygen (O 2 ) level for mixture with the exhaust gases, and/or a variety of other factors. For example, a small hybrid fireplace assembly  100 , which generates relatively fewer particulate emissions, requires a smaller overall air supply for combustion of the particulate emissions. Accordingly, the back wall chamber  340  may have relatively fewer rear air distribution holes  355 , or the back wall chamber may be omitted altogether. A large hybrid fireplace assembly  100 , which generates relatively more particulate emissions, typically requires a larger overall air supply for combustion of the particulate emissions. Accordingly, the back wall chamber  340  may have more rear air distribution holes  340  and/or larger rear air distribution holes  355 . 
         [0038]    Returning to  FIG. 2 , tertiary combustion takes place downstream of the secondary combustion tubes  230  and upstream of the catalytic converter  245 . The leading edge  220  of the baffle  205  forms an exhaust passageway  240  adjacent to the front wall  110  of the firebox  105 . The exhaust gases from the burning fire are directed from the lower combustion chamber  210 , through the exhaust passageway  240 , and into the upper combustion chamber  215 . A tertiary air supply mixes with the exhaust gases in the exhaust passageway  240 , removing additional particulate emissions. 
         [0039]    The tertiary air supply can be distributed into the firebox  105  from a variety of locations, such as an air wash passageway  255  adjacent to the interior of the front wall  110  and near the top of the front wall. The tertiary air supply in the illustrated embodiment is directed downwardly through the exhaust passageway  240  and across the face of the window  150 . In addition to removing particulate emissions from the exhaust gases, the tertiary air supply can help cool and/or clean the surface of the window  150 . 
         [0040]    As previously described, the hybrid combustion system includes both catalytic and non-catalytic components. Once the exhaust gases have passed through the primary, secondary, and tertiary combustion stages, the exhaust gases enter the catalytic combustion stage. Catalytic combustion takes place in the upper combustion chamber  215 . As previously described, the catalytic converter  245  is mounted above the baffle  205  so that all of the exhaust gases will pass through the catalytic converter  245  before entering the exhaust flue. The catalytic converter  245  is positioned rearward of the leading edge  220  of the baffle  205 , such that the exhaust gases mix with sufficient air during secondary and tertiary combustion to achieve desired oxygen (O 2 ) levels before entering the catalytic converter. In the illustrated embodiment, the desired oxygen level is within in the range of 5-6%, while other embodiments, the desired oxygen level falls within a different range. The desired oxygen level may be based in part on the size of the hybrid fireplace assembly  100 , in addition to other factors. If the catalytic converter  245  is positioned too close to the leading edge  220  of the baffle  205 , the exhaust gases may not mix with enough air during secondary and tertiary combustion, causing the catalytic converter to be used ineffectively. 
         [0041]      FIG. 4  is a front isometric view of the catalytic converter  245  of  FIG. 2 . The catalytic converter  245  is a honeycomb  410 , steel wool  405 , or other base or matrix structure coated with selected metals, such as precious metals or the like. The surface properties of these metals are such that particulate emissions that are too cool to burn on their own will ignite when they react with the catalytic converter  245 . In other words, the catalytic converter  245  provides a reaction with the components in the exhaust gas, such as the carbon monoxide, that causes portions of the catalytic converter to heat up to a temperature so as to cause the particulate emissions to burn and be substantially removed from the exhaust. In the illustrated embodiment, the catalytic converter  245  is serviceable, and may be removed for repair and/or replacement as necessary. 
         [0042]    The catalytic converter  245  reacts with the exhaust gases downstream of tertiary combustion and upstream of the flue adapter  165 , removing additional particulate emissions from the exhaust gases before these gases reach the flue adapter  165 . As previously discussed, at higher temperatures, the secondary combustion tubes  230 ,  320 ,  325 , and  330  are more effective at reducing particulate emissions, and the catalytic converter  245  is used relatively less. At lower temperatures, the secondary combustion tubes  230 ,  320 ,  325 , and  330  are less effective at reducing particulate emissions, and the catalytic converter  245  is used relatively more. Regardless of the temperature, the catalytic converter  245  is configured to allow sufficient air to flow therethrough in order to maintain an active flame in the firebox  105 . 
         [0043]    The catalytic converter  245  can be engaged and disengaged via a bypass damper.  FIG. 5  is a top isometric view of the fireplace assembly  100  of  FIG. 1  showing a bypass damper  505 . In some embodiments, a damper control (not shown) is provided to allow the user to selectively open and close the bypass damper  505 . The damper control can extend along the top plate  125  through a damper control opening  510 . When the bypass damper  505  is closed, the exhaust gases generated by the burning fire must flow through the catalytic converter  245  before reaching the flue adapter  165 . When the bypass damper is open, the exhaust gases may flow around the catalytic converter  245  and reach the flue adapter  165  without being processed by the catalytic converter. In the illustrated embodiment, the bypass damper  505  is downstream of the catalytic converter  245 . However, in other embodiments, the bypass damper  505  is located upstream of the catalytic converter  245 . 
         [0044]    The hybrid fireplace assembly  100  described herein allows for the use of a thinner catalytic converter  245  than those used in conventional catalytic fireplace assemblies. Conventional catalytic fireplace assemblies (which do not include non-catalytic secondary combustion tubes  230 ,  320 ,  325 , and  330 ) generally have catalytic converters that are 2-4″ thick, depending on the size of the firebox. Because the hybrid fireplace assembly  100  described herein reduces particulate emissions during primary, secondary, and tertiary combustion, there are fewer particulate emissions to be processed by the catalytic converter  245 . Accordingly, the hybrid fireplace assembly  100  allows for use of a thinner catalytic converter  245 . In some embodiments, the catalytic converter  245  employed by the hybrid fireplace assembly  100  is 1-2″ thick, depending on the size of the firebox  105 . That is, in some embodiments, the reduction in the size of the catalytic converter  245  over those used by conventional catalytic fireplace assemblies is approximately fifty percent. Among other benefits, the reduction in the size of the catalytic converter  245  lowers the cost of the catalytic converter, and thus the cost of the fireplace assembly  100 . 
         [0045]    The hybrid fireplace assembly  100  described herein achieves better particulate emission levels than both conventional catalytic fireplace assemblies and conventional non-catalytic fireplace assemblies having secondary combustion tubes. A standard catalytic fireplace assembly achieves a maximum particulate emission level of approximately 2.5 grams/hour, while a standard non-catalytic fireplace assembly having secondary combustion tubes achieves a maximum particulate emission level of approximately 4.5 grams/hour. In contrast, the hybrid fireplace assembly  100  described herein achieves a maximum particulate emission level of approximately 1.0 grams/hour. 
         [0046]    The above description of illustrated embodiments of the disclosure is not intended to be exhaustive or to limit the invention to the precise form disclosed. While specific embodiments of, and examples for, the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize. The teachings of the disclosure herein can be applied to other wood burning fireplace assemblies, not necessarily the assemblies described above. 
         [0047]    While certain aspects of the disclosure are presented below in certain claim forms, the inventors contemplate the various aspects of the disclosure in any number of claim forms. In general, in the following claims, the terms used should not be construed to limit the disclosure to the specific embodiments disclosed in the specification and claims, but should be construed to include all components and methods of manufacturing the components, in accordance with the claims. Accordingly, the disclosure is not limited by the description, but instead the scope of the disclosure is to be determined entirely by the claims. 
         [0048]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.