SINGLE BURN RATE POT STOVE WITH SECONDARY COMBUSTION

Abstract

A single burn rate stove including a burn chamber configured to burn biomass therein and a door configured to receive primary combustion air and provide the received primary combustion air to the burn chamber. The door is at a front of the stove. The stove further includes a bottom configured to receive secondary combustion air, a plurality of secondary air tubes extending across a top of the burn chamber, and a secondary air manifold configured to conduct the secondary combustion air from the bottom to the plurality of secondary air tubes.

Description

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates generally to biomass stoves. More particularly, this invention pertains to biomass stoves utilizing primary and secondary combustion.

Single burn rate pot stoves are cheap wood burning appliances typically used to heat cabins, tents, or other secondary or low cost shelters. Single burn rate pot stoves are typically configured to burn split wood or logs inserted into the burn chamber through a door in the front of the stove. Single burn rate pot stoves have thin walls to allow heat transfer into the space to be heated. Sing burn rate pot stoves also have a very hot top plate which can be cooked on. Single burn rate pot stoves are generally very inefficient resulting in large amounts of heat loss through the flue and relatively fast consumption of wood or biomass burned therein.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a single burn rate biomass stove (i.e., fixed burn rate stove) with improved burn efficiency and heat transfer to the area heated by the stove. Biomass (e.g., cut wood) is placed in the stove burn chamber through a door at the front of the stove and lit. The stove has a primary air intake in the door. The primary combustion air is routed from a top of the door to a bottom of the door and into the burn chamber. Secondary combustion air is taken in through a bottom of the stove at the front of the stove and routed under the burn chamber toward the back of the stove. A pair of secondary air manifolds receive the secondary combustion air and provide it to a plurality of air tubes extending across a top of the burn chamber. The secondary air manifolds are spaced apart from the sides of the burn chamber. The secondary combustion air is preheated as it travels under the bottom of the burn chamber and through the secondary air manifolds inside the burn chamber.

In one aspect, a single burn rate stove includes a burn chamber configured to burn biomass therein and a door configured to receive primary combustion air and provide the received primary combustion air to the burn chamber. The door is at a front of the stove. The stove further includes a bottom configured to receive secondary combustion air, a plurality of secondary air tubes extending across a top of the burn chamber, and a secondary air manifold configured to conduct the secondary combustion air from the bottom to the plurality of secondary air tubes.

In another aspect, a stove includes a burn chamber configured to burn biomass therein and a primary combustion airflow system configured to intake primary combustion air and direct the primary combustion air into the burn chamber. The stove further includes a secondary combustion airflow system configured to intake secondary combustion air, preheat the secondary combustion air, and direct the secondary combustion air into the burn chamber. The secondary combustion airflow system includes a secondary air intake configured to intake the secondary combustion air and at least one secondary air manifold fluidly connected to the secondary air intake. The at least one secondary air manifold is disposed within and extends from a bottom to a top of the burn chamber. The secondary combustion airflow system further includes a first air tube connected to and extending from the at least one secondary air manifold across the top of the burn chamber, the first air tube is configured to output the secondary combustion air into the burn chamber, and a second air tube connected to and extending from the at least one secondary air manifold across the top of the burn chamber. The second air tube is configured to output the secondary combustion air into the burn chamber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front isometric view of a single burn rate stove including secondary combustion.

FIG. 2 is a front isometric view of a pair of secondary air manifolds with a plurality of secondary air tubes extending therebetween of the stove of FIG. 1.

FIG. 3 is an elevated side perspective view of the secondary air manifolds and secondary air tubes of FIG. 2 showing an airflow path of secondary combustion air therethrough.

FIG. 4 is a front cutaway view of the stove of FIG. 1 showing an airflow path of secondary combustion air.

FIG. 5 is a side cutaway view of the stove of FIG. 1 showing airflow paths of primary combustion air, secondary combustion air, and exhaust gases.

Reference will now be made in detail to optional embodiments of the invention, examples of which are illustrated in accompanying drawings. Whenever possible, the same reference numbers are used in the drawing and in the description referring to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of the embodiments described herein, a number of terms are defined below. The terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a,” “an,” and “the” are not intended to refer to only a singular entity, but rather include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as set forth in the claims.

As described herein, an upright position is considered to be the position of apparatus components while in proper operation or in a natural resting position as described herein. As used herein, the upright and assembled orientation of a single burn rate wood stove with secondary combustion is when operating on a generally level surface such as shown in FIGS. 1, 4, and 5. Vertical, horizontal, above, below, side, top, bottom and other orientation terms are described with respect to this upright position during operation unless otherwise specified. The term “when” is used to specify orientation for relative positions of components, not as a temporal limitation of the claims or apparatus described and claimed herein unless otherwise specified. The terms “above”, “below”, “over”, and “under” mean “having an elevation or vertical height greater or lesser than” and are not intended to imply that one object or component is directly over or under another object or component.

The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without operator input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

Referring now to FIGS. 1-5, a single burn rate (i.e., fixed burn rate) biomass stove 10 is shown. The stove 10 has an outer cast shell 12 which includes a front wall 14, a back wall 16 opposite the front wall 14, side walls 18, a bottom 20, and a top 22, collectively defining a burn chamber 24 or firebox therein. The stove 10 has a primary airflow system 26 for introducing primary combustion air PA into the burn chamber 24 and a secondary airflow system 28 for introducing secondary combustion air SA at the top of the burn chamber 24 (FIG. 5). The stove 10 utilizes secondary combustion to improve burn efficiency, reduce emissions, and improve heat transfer into the space, e.g., the room, heated by the stove 10. In one embodiment, the sides of the stove are single layer (i.e., a single wall defines the outside edge of the burn chamber and the outside of the stove itself).

Biomass, e.g., cut wood, is placed in the stove burn chamber 24 through a door 30 of the front wall 14 and lit. The stove 10 has a primary air intake 32 at a top of the door 30 (FIG. 5). In one embodiment, the door 30 is double walled, and the primary combustion air PA is routed from a top of the door 30 to a bottom of the door 30 (FIG. 5). The primary combustion air PA enters the burn chamber 24 through an outlet 34 in the back of the door 30, at the bottom of the door 30. The primary air intake 32, a primary air conduit 36, and the outlet 34 define the primary combustion airflow system 26 which intakes and directs the primary combustion air PA into the burn chamber 24 (FIG. 5).

In one embodiment, the door 30 includes a window, with the intake 32 above the window and the outlet 34. The primary combustion air PA can enter the intake 32 above the window and exit the door 30 into the burn chamber 24 below the window. As shown, the stove 10 does not include a window.

The secondary airflow system 28 includes a secondary air intake 38, which intakes secondary combustion air SA through the bottom 20, a secondary air channel 40, at least one secondary air manifold 42, 44, and air tubes 46, 48, 50 structurally and fluidly connected to the at least one secondary air manifold 42, 44 for outputting the secondary combustion air SA into the burn chamber 24 (FIGS. 2-5). In one embodiment, the secondary airflow system 28 includes two secondary air manifolds 42, 44 and three air tubes 46, 48, 50 connected to each secondary air manifold 42, 44 at each end thereof (FIGS. 2-3).

The secondary combustion air SA enters the secondary air intake 38 at the bottom 20. In more detail, the bottom 20 comprises a bottom 52 of the burn chamber 24 and a bottom plate 54 spaced apart from and located below the bottom 52 of the burn chamber 24 (FIG. 5). Thereby, the secondary combustion air SA passes between the bottom 52 of the burn chamber 24 and the bottom plate 54, from the front toward the back of the stove 10.

The stove 10 preheats the secondary combustion air SA in multiple stages. The secondary combustion air SA is preheated as it passes under the burn chamber 24, through the secondary air manifolds 42, 44, and the air tubes 46, 48, 50. Initially, the secondary combustion air SA is preheated as it passes underneath the bottom 52 of the burn chamber 24. Thereafter, the secondary combustion air SA is further preheated as it passes from the bottom 52 of the burn chamber 24, through the secondary air manifolds 42, 44 inside the burn chamber 24. The secondary combustion air SA is further preheated as it passes through and out of the secondary air tubes 46, 48, 50. The secondary combustion air SA ignites the gases (e.g., smoke) in the burn chamber 24.

Each secondary air manifold 42, 44 is fluidly connected to the secondary air intake 38 and the secondary air channel 40. Each secondary air manifold 42, 44 is connected to and supported by a base plate 56, which in turn is connected to the bottom 52 of the burn chamber 24 via fasteners. Each secondary air manifold 42, 44 can extend below the base plate 56, and also the bottom 52 of the burn chamber 24, and reside at least partially within the secondary air channel 40. Each secondary air manifold 42, 44 is located within the burn chamber 24 and spaced apart from the front wall 14, the side walls 18, the top 22, and the back wall 16, which allows air to pass therebetween and preheat the secondary combustion air SA within the secondary air manifold(s) 42, 44. Each secondary air manifold 42, 44 extends from the bottom 52 of the burn chamber 24, at the back of the burn chamber 24 (i.e., next to the back wall 16), toward a top of the burn chamber 24. Therein, each secondary air manifold 42, 44 is configured to conduct the secondary combustion air SA toward the top of the burn chamber 24 and forward to the air tubes 46, 48, 50 at the top of the burn chamber 24.

Each secondary air manifold 42, 44 includes one or more portions 58, 60 (FIG. 2). The portions 58, 60 of each secondary air manifold 42, 44 can mirror one another. For example, each secondary air manifold 42, 44 can include a first, substantially vertical portion and a second, substantially horizontal portion 60. The first portion 58 is connected to the bottom 52 of the burn chamber 24, via the base plate 56, and is further fluidly coupled to the secondary air intake 38. The first portion 58 extends substantially upwardly and vertically from the bottom 52 of the burn chamber 24. The second portion 60 is fluidly coupled to the first portion 58. The second portion 60 extends substantially laterally and horizontally from the first portion 58. The second portion 60 is perpendicular to the first portion 58. The second portion 60 mounts the air tubes 46, 48, 50. The second portion 60 does not include air outlets; thereby, the secondary combustion air only enters the burn chamber 24 through the secondary air tubes 46, 48, 50. In one embodiment, the second portions 60 may include locating and support features 62 that mate with respective mounting features (unnumbered) on the side walls 18 for properly installing and supporting the secondary air manifolds 42, 44.

The secondary air tubes 46, 48, 50 extend across the top of the burn chamber 24 between the pair of secondary air manifolds 42, 44. The secondary air tubes 46, 48, 50 may be rigidly or removably connected to the secondary air manifolds 42, 44 at each end thereof. As a result of each end of each air tube 46, 48, 50 being connected to the respective secondary air manifolds 42, 44, the secondary combustion air SA is simultaneously fed into each end of each air tube 46, 48, 50, resulting in an even distribution of the secondary combustion air SA across a length of each air tube 46, 48, 50 (as illustrated by the length of each airflow arrow of the air tubes 46, 48, 50 in FIGS. 2-5).

Each air tube 46, 48, 50 includes at least one set of air outlets 46A, 48A, 50A for outputting the secondary combustion air SA into the burn chamber 24 (FIG. 2). In one embodiment, the air tubes 46, 48, 50 can include two sets of air outlets to direct the secondary combustion air SA forward and down as the secondary combustion air SA enters the burn chamber 24. In one embodiment, the air tubes 46, 48, 50 can include air outlets that direct the secondary combustion air SA to the front of the burn chamber 24. In one embodiment, a first air tube 46 can include two or more sets of air outlets and a second air tube 48, 50 can include a single set of air outlets such that the secondary combustion air SA is unevenly and only distributed into the burn chamber 24 by the secondary air tubes 46, 48, 50.

In yet another embodiment, the first, distal air tube 46, which is located next to a proximal end of the second portions 60 of the secondary air manifolds 42, 44 next to the front of the burn chamber 24, can include three sets of outlets 46A, 46B, 46C that are oriented differently from one another to individually distribute the secondary combustion air SA into the burn chamber 24 (FIGS. 2-3). In more detail, the first air tube 46 can include front facing air outlets 46A located at a front thereof and configured to direct the secondary combustion air SA substantially horizontally and forwardly toward the front of the burn chamber 24, rear facing outlets 46B located at a back thereof and configured to direct the secondary combustion air SA substantially horizontally and rearwardly toward the back of the burn chamber 24, and downward facing outlets 46C located at a bottom thereof and configured to direct the secondary combustion air SA substantially vertically downward toward the bottom 52 of the burn chamber 24. The second air tube 48, which is located distally of the first air tube 46 on the secondary air manifolds 42, 44, can include a single set of air outlets 48A such as front facing outlets 48A located at a front thereof and configured to direct the secondary combustion air SA substantially horizontally and forwardly toward the front of the burn chamber 24. The third air tube 50, which is located distally of the second air tube 48 on the secondary air manifolds 42, 44, can include a single set of air outlets 50A such as front facing outlets 50A located at a front thereof and configured to direct the secondary combustion air SA substantially horizontally and forwardly toward the front of the burn chamber 24.

Thereby, the secondary combustion air SA can be unevenly distributed within the burn chamber 24, via the air tubes 46, 48, 50 for creating more turbulent airflow next to an exhaust outlet 64, augmenting the secondary combustion burn rate for burning more matter during secondary combustion (FIG. 5). Furthermore, the second and third air tubes 48, 50 significantly increase the secondary combustion burn rate as the additional airflow therefrom increases turbulent airflow near the exhaust outlet 64, as such forward airflow is directed toward the rearwardly directed airflow of the rear facing air outlets 46B of the first air tube 46. Specifically, the third air tube 50 significantly increases the secondary combustion burn rate because the forwardly directed airflow therefrom, which is introduced rearwardly of a center point of the burn chamber 24, creates a counterclockwise flow of air within the burn chamber 24 and causes significantly more turbulent airflow near the exhaust outlet 64 as compared to just the airflow introduced by the first air tube 48. Conventional wisdom in the art suggested that a third air tube 50 would increase laminar airflow of the secondary combustion air SA, as such airflow from the third air tube 50 would seemingly magnify the parallel airflow of the second air tube 48 and thereby reduce the secondary combustion burn rate. However, the third air tube 50 creates multiple turbulent airflow areas T1, T2, T3, as illustrated in phantom in FIG. 5, respectively located underneath the second air tube 48, in between the first and second air tubes 46, 48, and underneath the first air tube 46.

The stove 10 can further include a baffle 66 above the secondary air tubes 46, 48, 50, which forms the top 66 of the burn chamber 24, a top plate 68 located above the baffle 66 with one or more integrated cooking surfaces (unnumbered), and a flue 70 or stovepipe at the back of the stove 10 with a butterfly valve (unnumbered) therein (FIGS. 1 and 5). Exhaust gases EG from the burn chamber 24 reach the top plate 68 by rising above a front of the baffle 66 and subsequently travel toward the back of the stove 10 under the top plate 68 to exit through the flue 70. In more detail, exhaust gases EG exit the burn chamber 24 by passing through the exhaust outlet 64, above the baffle 66 at the front of the baffle 66 between the front edge of the baffle 66, and the inside of the front of the stove 10. The exhaust gases EG travel rearward under a top plate 68 to the flue 70 to be exhausted from the room being heated by the stove 10.

This written description uses examples to disclose the invention and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

It is contemplated within the scope of the claims that the plurality of secondary air tubes may not be identical components. It is contemplated within the scope of the claims that although a plurality of secondary air tubes may be substantially identical, a stove may include secondary air tubes within the plurality that differ in shape, size, and number and location of air outlets.

It will be understood that the particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention may be employed in various embodiments without departing from the scope of the invention. Those of ordinary skill in the art will recognize numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All of the compositions and/or methods disclosed and claimed herein may be made and/or executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of the embodiments included herein, it will be apparent to those of ordinary skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.

Thus, although there have been described particular embodiments of the present invention of a new and useful SINGLE BURN RATE POT STOVE WITH SECONDARY COMBUSTION it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.

Claims

1. A single burn rate stove comprising: a burn chamber configured to burn biomass therein;a door configured to receive primary combustion air and provide the received primary combustion air to the burn chamber, wherein the door is at a front of the stove;a bottom configured to receive secondary combustion air;a plurality of secondary air tubes extending across a top of the burn chamber, wherein the plurality of secondary air tubes comprises: a first air tube comprising a first set of air outlets;a second air tube comprising a second set of air outlets; anda third air tube comprising a third set of air outlets, wherein the first, second, and third air outlets are each directed to a front of the burn chamber; anda secondary air manifold configured to conduct the secondary combustion air from the bottom to the plurality of secondary air tubes.

2. The single burn rate stove of claim 1, wherein: the bottom comprises a bottom of the burn chamber and a bottom plate spaced apart from the bottom of the burn chamber; andthe secondary combustion air enters the bottom at the front of the stove.

3. The single burn rate stove of claim 1, wherein: the bottom comprises a bottom of the burn chamber and a bottom plate spaced apart from the bottom of the burn chamber;the secondary combustion air enters the bottom at the front of the stove; andthe secondary air manifold receives the secondary combustion air from the bottom of the burn chamber at a back of the burn chamber opposite the front of the stove.

4. The single burn rate stove of claim 1, wherein: the bottom comprises a bottom of the burn chamber and a bottom plate spaced apart from the bottom of the burn chamber;the secondary combustion air enters the bottom at the front of the stove;the secondary air manifold receives the secondary combustion air from the bottom of the burn chamber at a back of the burn chamber opposite the front of the stove;the secondary air manifold is spaced apart from a side of the burn chamber; andthe secondary air manifold is spaced apart from the back of the burn chamber.

5. The single burn rate stove of claim 1, wherein: the bottom comprises a bottom of the burn chamber and a bottom plate spaced apart from the bottom of the burn chamber;the secondary combustion air enters the bottom at the front of the stove;the secondary air manifold receives the secondary combustion air from the bottom of the burn chamber at a back of the burn chamber opposite the front of the stove;the secondary air manifold is a first secondary air manifold spaced apart from a first side of the burn chamber and spaced apart from the back of the burn chamber;the first secondary air manifold connects to a first end of each secondary air tube of the plurality of secondary air tubes;the stove further comprises a second secondary air manifold configured to receive secondary combustion air from the bottom of the burn chamber and provide the secondary combustion air to a second end of each secondary air tube of the plurality of secondary air tubes opposite the first end of each secondary air tube of the plurality of secondary air tubes; andthe second secondary air manifold is spaced apart from the back of the burn chamber and spaced apart form a second side of the burn chamber opposite the first side of the burn chamber.

6. The single burn rate stove of claim 1, wherein: the door is configured to selectively open to enable placing the biomass in the burn chamber.

7. The single burn rate stove of claim 1, wherein: the door is configured to receive the primary combustion air at a top of the door and provide the primary combustion air to the burn chamber at a bottom of the door.

8. The single burn rate stove of claim 1, wherein: the first air tube is connected to the secondary air manifold next to a proximal end of the secondary air manifold, the first air tube comprising three sets of air outlets, the first set of air outlets being one of the three sets of air outlets;the second air tube is connected to the secondary air manifold and located distally of the first air tube, the second air tube comprising a single set of air outlets, the second set of air outlets being the single set of air outlets.

9. (canceled)

10. (canceled)

11. A stove comprising: a burn chamber configured to burn biomass therein;a primary combustion airflow system configured to intake primary combustion air and direct the primary combustion air into the burn chamber; anda secondary combustion airflow system configured to intake secondary combustion air, preheat the secondary combustion air, and direct the secondary combustion air into the burn chamber, the secondary combustion airflow system comprising: a secondary air intake configured to intake the secondary combustion air;at least one secondary air manifold fluidly connected to the secondary air intake, the at least one secondary air manifold disposed within and extending from a bottom to a top of the burn chamber;a first air tube connected to and extending from the at least one secondary air manifold across the top of the burn chamber, the first air tube configured to output the secondary combustion air into the burn chamber, the first air tube comprising a first set of air outlets directed to a front of the burn chamber; anda second air tube connected to and extending from the at least one secondary air manifold across the top of the burn chamber, the second air tube configured to output the secondary combustion air into the burn chamber, the second air tube comprising a second set of air outlets directed to the front of the burn chamber.

12. The stove of claim 11, wherein: the at least one secondary air manifold comprises a first manifold and a second manifold spaced apart from the first manifold;each first and second air tube is connected to and extends between the first manifold and the second manifold such that the secondary combustion air is simultaneously fed into each end of each first and second air tube, respectively by the first manifold and the second manifold, resulting in an even distribution of the secondary combustion air across a length of each first and second air tube.

13. The stove of claim 11, wherein: the first air tube comprises two or more sets of air outlets;the second air tube comprises a single set of air outlets such that the secondary combustion air is unevenly and only distributed into the burn chamber by the first and second air tubes.

14. The stove of claim 11, wherein: the first air tube comprises three sets of air outlets, each set oriented differently from one another to individually distribute the secondary combustion air into the burn chamber; andthe second air tube comprises a single set of air outlets.

15. The stove of claim 11, wherein: the first air tube comprises: the first set of air outlets located at a front of the first air tube and configured to direct the secondary combustion air horizontally and forwardly toward a front of the burn chamber;rear facing outlets located at a back of the first air tube and configured to direct the secondary combustion air horizontally and rearwardly toward a back of the burn chamber; anddownward facing outlets located at a bottom of the first air tube and configured to direct the secondary combustion air vertically downward toward the bottom of the burn chamber; andthe second air tube comprises: front facing outlets located at a front of the second air tube and configured to direct the secondary combustion air horizontally and forwardly toward the front of the burn chamber.

16. The stove of claim 11, wherein: the at least one secondary air manifold comprises a proximal end located next to a front of the burn chamber;the first air tube is located next to the proximal end of the at least one secondary air manifold; andthe second air tube is located distally of the first air tube on the at least one secondary air manifold.

17. The stove of claim 11, further comprising: a third air tube connected to and extending from the at least one secondary air manifold across the top of the burn chamber, the third air tube configured to output the secondary combustion air into the burn chamber.

18. The stove of claim 17, wherein: the at least one secondary air manifold comprises a proximal end located next to a front of the burn chamber;the first air tube is located next to the proximal end of the at least one secondary air manifold;the second air tube is located distally of the first air tube on the at least one secondary air manifold; andthe third air tube is located distally of the second air tube on the at least one secondary air manifold.

19. The stove of claim 11, wherein: the at least one secondary air manifold is disposed within the burn chamber so that a primary combustion of the biomass in the burn chamber preheats the secondary combustion air passing through the at least one secondary air manifold and each first and second air tube.

20. The stove of claim 11, wherein: the at least one secondary air manifold comprises: a first portion connected to the bottom of the burn chamber and fluidly coupled to the secondary air intake, the first portion extending substantially upwardly and vertically from the bottom of the burn chamber; anda second portion fluidly coupled to the first portion, the second portion extending substantially laterally and horizontally from the first portion, and the second portion mounting the first and second air tubes.