GB2533040A

GB2533040A - Stove

Info

Publication number: GB2533040A
Application number: GB1521530.4A
Authority: GB
Inventors: Peter Van Vuuren David; Jonathan Turner James
Original assignee: JETMASTER FIRES Ltd
Current assignee: JETMASTER FIRES Ltd
Priority date: 2015-12-07
Filing date: 2015-12-07
Publication date: 2016-06-08
Anticipated expiration: 2035-12-07
Also published as: GB2533040B; GB201521530D0

Abstract

A stove (2, Fig. 1A) for burning fuel comprises a fuel chamber 8, a viewing window 24 at a front side of the chamber 8, and an airwash passage 50 for passing external air along the inside of the window 24. An airwash control 54 adjusts the amount of air provided by the airwash passage 50. A combustion air channel 70 passes external air via a ceiling portion 78 which extends along a ceiling 11 of the chamber 8 in a direction towards or away from the front of the chamber 8 to one or more combustion air outlets (82, Fig. 12) which are further from the front of the chamber 8 than an outlet of the airwash passage 50. A gas outlet hole 30 may be formed in the ceiling of the chamber 8. The combustion air channel 70 may comprise a tubular channel having air inlets (72, Fig. 11) a bend or serpentine section (120, Fig. 13B). The window 24 may be formed in a door (20, Fig. 1B). A method of burning fuel in the stove (2, Fig. 1A) is also claimed.

Description

STOVE

The present technique relates to a stove for burning fuel.

A stove for burning fuel (e.g. wood, wood pellets, biomass or charcoal) can be used as a heating appliance within the home. The visual appearance of the stove when burning the fuel can be an important consideration when designing such a stove. For example, many users may consider the stove not merely as a heating appliance, but also as a decorative feature of the room in which the stove is located. Typically, the user will wish to see the flames while the fire is burning, and so a viewing window is typically provided at a front side of the chamber in which the fuel is burnt. The burning fuel typically releases various combustion products. For example, burning wood may release carbon particles or soot, wood tars, hydrocarbons, etc. These combustion products may condense on the viewing window, so that the viewing window may quickly become dirty and prevent the user seeing the flames. For this reason, virtually all stoves are provided with an airwash passage which draws in air from outside the chamber and directs the air along the inside of the viewing window. By passing a curtain of air along the viewing window, the dirty combustion products released by the fuel when burning can be prevented from settling on the window, keeping the viewing window clean and hence improving the visual appearance of the stove.

Since the fire may require a certain amount of air (oxygen) to support combustion, and the airwash passage provides a relatively large volume of air sufficient for maintaining the fire, the airwash passage is also typically used as the main air source for the combustion while the fire is burning.

At least some examples provide a stove for burning fuel, comprising: a chamber for receiving the fuel; a viewing window at a front side of the chamber; at least one airwash passage configured to pass air from outside the chamber along the inside of the viewing window; an airwash control configured to adjust an amount of air provided by said at least one airwash passage; and at least one combustion air channel configured to pass air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of said at least one airwash passage.

The stove according to the present technique is provided with at least one combustion air channel for passing air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of the airwash passage. An airwash control is also provided to adjust an amount of air provided by the airwash passage.

The inventors found that, surprisingly, using the airwash as the primary source of air for combustion when the fire is up to temperature reduces the efficiency of combustion. For efficient combustion, it is desirable to be able to burn not only the fuel itself but also the combustion products emitted from the fuel when the fuel is burnt. For example, for a wood-burning stove, when the wood is charred it releases various combustion products including carbon monoxide gas, carbon particles or soot, wood tars and various hydrocarbons such as formaldehyde or acetaldehyde. However, the air provided by the airwash passage typically does not support efficient combustion of these combustion products, for two reasons.

Firstly, combustion of the combustion products typically requires relatively hot air to be provided, but the air from the airwash passage passes along the inside of the viewing window which is typically the coldest part of the stove, and so when the airwash air enters the chamber it is not hot enough to burn the combustion products efficiently. Also, since the airwash is provided to guide air along the viewing window, it is by definition located at the very front side of the chamber. The stove may have a chimney or flue for releasing smoke from the burning fire, and the air from the airwash typically rushes in off the viewing window from the front side, and tends to blow the combustion products from the burning fuel straight up the chimney before they have fully combusted.

In contrast, since the air outlets of the at least one combustion air channel are positioned further from the front side than the airwash passage, they are less likely to blow the combustion products up the chimney. Also the ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber enables the air provided by the combustion air channel to be heated before it is injected. The region of the chamber near the ceiling is typically one of the hottest parts of the stove because hot gases released by the burning fuel tend to rise to the ceiling, so by passing air through a channel along the ceiling of the chamber, the air can be preheated before it is emitted into the chamber to increase the efficiency of combustion of the combustion products.

Therefore, by using the combustion air channel as the primary source of air once the fire is up to temperature, more efficient combustion can be achieved. An airwash control is provided which allows the user to adjust the amount of air provided by the airwash passage. The airwash passage is still useful to prevent the viewing window getting dirty when the fire has only just been lit and the fire is warming up to temperature, but when the fire is hot enough to burn the combustion products, the airwash control can be used to shut off the airwash passage (or at least reduce the amount of airwash air to less than the amount of air provided by the at least one combustion air channel), and then the at least one combustion air channel can be used as the main source of combustion air to support combustion. This is counterintuitive since the convention in this field is that the airwash always needs to be provided to keep the viewing window clean, to satisfy the aesthetic requirements for the stove. However, by increasing the efficiency with which combustion products such as tars and soot are burnt using air from the combustion air channel, the dirty combustion products are burnt off rapidly and so will not settle on the viewing window anyway. Therefore, surprisingly there is no need for the airwash during the main burning phase of the fire when the fire is sufficiently hot to burn the combustion products. Therefore, providing a combustion air channel as discussed above can greatly improve the efficiency of the stove, so that more of the available energy can be extracted from a given amount of fuel. Also, the smoke emitted by the stove is cleaner as it contains less of the dirty combustion products such as the tars and soot, so the stove is more environmentally friendly. Another benefit is that the ash produced by the stove is finer and less ash is produced, so that the stove requires less cleaning.

At least one of the combustion air outlets of the at least one combustion air channel may be configured to direct air into the chamber from the ceiling of the chamber. While it would be possible for a combustion air channel to pass air through the at least one ceiling portion along the ceiling of the chamber and then down to one or more outlets located at a lower part of the chamber than the ceiling, more efficient combustion can be achieved by providing at least some of the combustion air outlets on the ceiling itself, because combustion gases emitted by the fuel when burning tend to collect near the ceiling, and so by injecting pre-heated air directly into the region containing these gases, the combustion gases can burn more efficiently.

The stove may have a gas outlet hole in the ceiling of the chamber. The gas outlet hole may lead to a passageway or cavity which extends to the flue or chimney of the stove for emitting exhaust gases produced by combustion. At least one of the combustion air outlets of the at least one combustion air channel may be positioned further from the front side of the chamber than the gas outlet hole. Hence, the combustion air channel outputs the pre-heated air at a point of the chamber further back than the gas outlet hole, which means that, unlike the airwash, the combustion air channel is less likely to wash the combustion gases straight up the gas outlet hole and out through the chimney.

Also, a barrier may be provided on the ceiling of the chamber between the gas outlet hole and at least one of the one or more combustion air outlets. This barrier traps combustion gases behind it to make it harder for the combustion gases to escape up the gas outlet hole until they have been burnt.

The at least one combustion channel may include a protruding part which protrudes from the ceiling of the chamber. For example, part of the combustion channel may be formed by a tubular portion which extends along the ceiling substantially parallel to the ceiling with a lower side edge of the tube positioned lower than the ceiling itself. By providing a channel which protrudes from the ceiling, the hot combustion gases rising to the ceiling flow along the ceiling and are forced over the protruding part, which increases the turbulence of the flow of the combustion gases. By encouraging more turbulence, this improves the mixing of the combustion gases with oxygen from the air provided by the combustion air channel, which improves the efficiency of combustion.

At least one of the combustion air outlets may be formed in the protruding part of the combustion air channel. Hence, as the combustion gases wash past the protruding part, air which has been preheated as it extends through the ceiling portion is injected into the gases and this causes turbulent mixing of the combustion gases with the oxygen from the injected air, which increases combustion efficiency.

The at least one combustion air channel may have a number of combustion air outlets at different orientations relative to the chamber. For example, air can be injected into the chamber at different angles. For example, when the protruding part is provided on the ceiling as discussed above, the combustion air outlets may be formed at different points about the perimeter of the protruding part. By injecting air at different angles into the chamber this further promotes turbulent flow of the combustion gases and mixing of the combustion gases with the injected air, to improve combustion efficiency.

The at least one combustion air channel may take a wide variety of paths between one or more air inlets where air is drawn in from outside the chamber and the combustion outlets. The air inlets for the combustion air channel could be located at a range of positions on the stove, but in general air is drawn in and passed via the at least one ceiling portion which extends along the ceiling in a direction towards or away from the front side, and out through the combustion air outlets into the chamber.

The hotter the air provided by the at least one combustion air channel, the greater the efficiency with which the combustion gases can be burnt. To increase the amount of heating of the air as it travels through the combustion air channel, an indirect path may be provided between the air inlets and the combustion air outlets, so that the air does not travel along the most direct route between the inlets and outlets. For example, the at least one combustion air channel may include at least one bend where the air travels around a bent portion of the channel. By passing the air along a relatively tortuous route along or through the chamber, the air can be made hotter at the point when it is injected into the chamber to increase the combustion efficiency.

In some examples the combustion air channel may include a serpentine portion which passes the air from outside the chamber along a serpentine path along or through the chamber to at least one of the combustion air outlets. By providing a channel which snakes back and forth along or through the chamber, the length of travel of the combustion air is increased and the amount of preheating can therefore be increased to improve the combustion efficiency. The serpentine portion could be formed along any of the walls of the chamber, including the back wall of the chamber opposite the viewing window, the left or right side walls, or along the ceiling of the chamber.

In some examples the at least one combustion air channel may draw air in near the top of the chamber and then pass it along the ceiling portion to the outlets. However, greater heating can be achieved if the air is passed from outside the chamber to the ceiling portion via a rising portion which extends from a lower portion of the chamber towards the ceiling of the chamber. By drawing air in lower down in the stove and passing it from a lower portion of the chamber up to the ceiling, this increases the distance travelled and so increases the amount of pre-heating of the combustion air.

In some cases the at least one combustion air channel may include a firebed portion which extends along or below a firebed of the chamber (the firebed is the portion of the chamber containing the fuel being burnt). For example, air can be drawn in at the base of the stove, passed along or below the firebed, and then up through one or more rising portions up to the at least one ceiling portion where it is passed along the ceiling in a direction towards or away from the front side of the chamber and onto one or more combustion air outlets to inject air into the chamber from above. Since the fire bed is another part of the chamber which becomes relatively hot when the fire is burning, passing the at least one combustion air channel through, along or below the firebed portion further improves the combustion efficiency by providing greater heating.

In some examples, only one combustion air channel may be provided. However, it is also possible to provide two or more independent combustion air channels with separate air inlets and air outlets.

The combustion air channel may also have at least one further combustion air outlet which is at a lower part of the chamber than the one or more combustion air outlets reached via the ceiling portion. The air emitted from the further combustion air outlet need not pass through the ceiling portion. For example, in addition to the combustion air outlets for injecting air from the ceiling of the chamber to support burning of the combustion products, then may also be some additional air outlets which inject air at the base of the fire to support burning of the fuel itself.

In some embodiments, the at least one combustion air channel may comprise a tubular channel having air inlets at both ends for drawing in air from outside the chamber, and the one or more combustion air outlets may be at an intermediate part of the channel between the air inlets. By providing a double ended channel with air inlets at both ends and the combustion air outlets in the middle of the channel, this can provide a more symmetric distribution of the air into the chamber than a channel in which air is drawn in only at one end and output at the other. The tubular channel could have a circular cross section or a non-circular cross section (e.g. an elliptical or rectangular cross section could be used). When such a double ended tubular channel is provided, then the combustion air channel may have at least two ceiling portions which extend along the ceiling of the chamber in the direction towards or away from the front side of the chamber, with at least one ceiling portion on each side of the intermediate part which includes the combustion air outlet. For example, a tubular channel may be provided with air inlets at the base of the stove on either side, rising portions in the back left and back right corners of the chamber (where the left/right side walls meet the back wall), two ceiling portions which extend along the ceiling of the chamber where the ceiling meets the left/side walls respectively, and an intermediate part extending between the two ceiling portions which includes a number of combustion air holes for injecting air into the chamber from the ceiling. Such a channel has been found to be relatively cheap to manufacture while providing a sufficiently long air channel for heating the air hot enough to support combustion of the combustion gases.

The at least one combustion air channel may be formed in different ways. In some examples the combustion air channel may comprise a one-piece channel. For example, the channel could be a continuous tube. This simplifies manufacturing and also reduces the chance of air leaking out from joins in the channel.

Alternatively the channel could be formed from two or more pieces which slot together with a relatively tight join (e.g. a sleeve fit or screw fit) to reduce air leakage.

In some cases at least part of the conversion air channel could be formed from a passageway within a frame of the chamber. A tubular portion could then extend through the chamber itself to provide air from the frame portions of the channel to the desired location within the chamber.

Alternatively, the combustion air channel could be formed entirely outside the chamber, without any portion extending inside the chamber. For example, a passage may extend back and forth above the ceiling of the chamber, leading to air outlets which inject the air through the ceiling into the chamber. By forming the ceiling of the chamber from a heat-conductive material, the hot combustion products gathering at the ceiling can heat the air inside the channel above the ceiling, so that hot air is injected into the combustion products.

The combustion air channel may also provide other functions in addition to providing air for supporting combustion. For example part of the combustion air channel could provide structural support for another part of the stove, such as a roof of the chamber or an airwash baffle for guiding the air from the airwash passage down the inside of the viewing window.

For example, the combustion channel may include a rigid tubular portion extending across enough of the ceiling of the chamber to support the heat-insulating board forrning the roof of the chamber.

In some examples, the viewing window may be provided on a static wall of the chamber at the front side of the chamber, and there may be a separate loading hatch for placing the fuel to be burnt inside the chamber. However, often there may be a door at the front side of the chamber and the viewing window may be formed in the door. The door can then be opened to insert the fuel and then swung back shut to locate the viewing window at the front side.

The front side of the chamber may be considered to be the side containing the main viewing window of the stove, or the side where the door of the stove is situated. The front side may be the side which would face into the room being heated by the stove when the stove is installed (as opposed to the closed back side of the chamber which would face the wall).

In some stoves, a viewing window could also be formed in one or both of the left and right side walls of the chamber, to provide further visibility of the fire.

At least some examples provide a method for burning fuel in a stove comprising a chamber for receiving the fuel, a viewing window at a front side of the chamber, at least one airwash passage configured to pass air from outside the chamber along the inside of the viewing window, and at least one combustion air channel configured to pass air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of said at least one airwash passage; the method comprising: lighting a fire in the chamber; passing air along the inside of the viewing window using the at least one airwash passage while the fire heats up; and when the fire is up to temperature, reducing an amount of air provided by the at least one airwash passage to less than an amount of air provided by the at least one combustion air channel.

By reducing the amount of air provided by the at least one airwash passage to less than the amount of air provided by the at least one combustion air channel when the fire is up to temperature, more efficient combustion is possible than in conventional stoves. This leads to cleaner ash, cleaner smoke emitted by the stove and more useful energy extracted from a given amount of fuel. This is surprising since a skilled person would regard maintaining the airwash while the fire running as essential in order to keep the viewing window clean. However, by improving combustion efficiency the need for cleaning the viewing window is reduced because the combustion products are burnt off anyway.

Further aspects, features and advantages of the present technique will be apparent from the following description of examples, which is to be read in conjunction with the accompanying drawings, in which: Figure 1A schematically illustrates an example of a stove for burning fuel; Figure 1B shows the stove with its door open; Figure 2 shows a front view of the stove; Figure 3 shows a front view of the stove with the door hidden; Figure 4 shows a cross section of the stove when viewed from the side; Figure 5 shows an isometric view of the inside of the chamber; Figure 6 shows the stove when viewed from below; Figure 7 shows a view of the stove from the left hand side; Figure 8 shows a view of the stove from the rear side; Figure 9 shows a view of the stove from the right hand side; Figure 10 shows a plan view of the stove from above; Figure 11 shows a combustion air channel for providing air into the chamber; Figure 12 shows an example of combustion air outlets provided at different orientations on the channel; Figures 13A to 13D show four examples of different paths which can be taken by the combustion air channel between air inlets and the air outlets; Figure 14 shows a second embodiment of a combustion air channel Figure 15 shows an example of forming the combustion air channel from two or more pieces; Figure 16 shows an example where part of the frame of the chamber forms the combustion air channel; Figure 17 shows a method of burning fuel in the stove.

Figures 1 to 10 show various views of a stove 2 for burning fuel. The fuel may include wood, wood pellets (e.g. derived from sawdust), biomass, coal or charcoal, or other kinds of fuel. Some stoves may be designed specifically for one type of fuel, e.g. a wood-burning stove, while other stoves may be multi-fuel stoves which are capable of burning different types of fuel. As shown in Figure 1A, the stove 2 comprises a substantially rectangular (cuboid) housing 4 which is raised from the floor supported by feet 6. Inside the housing 4 is formed a chamber 8 for receiving the fuel to be burnt. The base of the chamber comprises a fire brick or other heat proof material, and the left, right and back walls and the ceiling of the chamber 8 are formed from heat insulating boards 10 (see Figures 4 and 5). For example, the boards 10 may be made from fire clay. Near the base of the chamber is provided a grate 12 for supporting the fuel to be burnt. The grate 12 is placed a short distance above the bottom of the chamber with a space below the grate 12 in which an ashtray 14 is provided. The grate 12 includes a number of slots or holes 16 so that ash produced when burning the fuel can drop through the slots 16 into the ashtray 14. The ashtray 14 can be removed from the front side of the stove and emptied when necessary. A fire guard 18 extends upwards from the front side of the grate 12 to enclose the fuel being burnt and prevent it falling out of the chamber 8.

A door 20 is attached by hinges 22 to the front side of the stove. The door 20 can be opened as shown in Figure 1B to allow fuel to be inserted into the chamber on the grate 12, and closed as shown in Figure 1A with the door forming the front wall of the chamber. A viewing window 24 is formed within the door 20 to allow the user to view the flames of the fire when the fire is burning inside the chamber 8. The viewing window 24 can be made of glass, glass-ceramic, or a transparent plastic such as polycarbonate for example. Figure 2 shows a front view of the stove to when the door 20 is shut. As shown in Figure 2, a latch 26 is provided to hold the door shut. The latch 26 can be released by turning a handle 28. It will be appreciated that the latch 26 is just one example of a mechanism for securing the door closed.

As shown in the cross-section view in Figure 4, a gas outlet hole 30 is provided in the ceiling of the chamber for emitting exhaust gases produced when burning the fuel. The gases pass through the gas outlet hole 30 into a cavity 32 at the top of the housing 4 (above the roof 10 of the chamber). As shown in the rear and plan views in Figures 8 and 10, a flue outlet 34 is provided in the housing of the stove 2 for coupling to a flue or chimney in order to pass the exhaust gases to outside the building in which the stove is situated. As shown in Figures 8 and 10, two (or more) alternative flue openings 34 may be provided to provide flexibility in the relative positioning of the chimney relative to the stove. For example, one flue outlet hole 34 may be provided in the top of the housing as shown in Figure 10, while another flue outlet hole 34 may be provided in the back of the housing as shown in Figure 8.

The top flue opening allows the stove to be positioned immediately below the chimney while the back flue opening 34 enables the stove to be positioned further forward relative to the chimney. The flue opening 34 which is not required for a given installation can be shut off by attaching a cover, while the other flue opening 34 is connected to the flue or chimney. Hence, smoke from the fire passes out of the chamber through the gas outlet hole 30 in the ceiling of the chamber into cavity 32 and then out of one of the flue outlet holes 34 and out through the flue to the outside.

As shown in Figure 4, when wood or other fuel 40 is burnt on the grate 12, various combustion products 42 are released. The combustion products 42 may for example include gases such as carbon dioxide or carbon monoxide, carbon particles or soot, hydrocarbons such as formaldehyde, and wood tars or other kinds of tar. The combustion products 42 are generally gaseous or contain small solid particles dispersed through other gaseous products, and are hot so tend to rise towards the ceiling of the chamber 8.

The viewing window 24 is typically one of the colder parts of the stove since it is exposed to the room or space being heated by the stove, and so it is more prone to the collection of particulates. To prevent combustion products 42 condensing on the viewing window 24 while the fire is heating up to temperature, which would make the viewing window dirty and prevent the user seeing the flames of the fire, an airwash passageway 50 is provided to draw in air from outside the chamber and pass it down the inside of the viewing window 24 (see Figure 4) . As shown in Figure 6, the airwash passageway comprises a pair of tubular channels 50 in the front left and front right corners of the housing 4. Figure 6 shows a view underneath the stove. In this example, the airwash passageways 50 have a rectangular cross-section, but it will be appreciated that other shapes can be provided. As shown in Figure 4, the airwash passageways 50 to the top of the chamber. As shown in Figure 5, an airwash baffle 52 extends laterally along the front of the chamber at the top of the stove. As shown in Figure 4, the airwash baffle 52 is angled down from the ceiling of the chamber to point towards the viewing window 24. As the wood 40 is charred, it burns off oxygen in the chamber 8, lowering the air pressure, which causes air to be drawn in from outside of the chamber up through the airwash passageways 50 and laterally along the width of the airwash baffle 52. The air then washes down over the front of the baffle 52 and along the inside of the viewing window 24, as shown in Figure 4. Effectively the airwash 50, 52 provides a curtain of air in front of the viewing window which prevents combustion products 42 settling on the viewing window and condensing. This helps to keep the glass of the viewing window 24 clean while the fire is heating up to temperature. As shown in Figure 6, an airwash control 54 is provided to control the amount of air provided by the airwash 50. A pair of plates 56 are attached to a cross bar 58 and a control lever 60. When the user pulls the control lever 60 forwards, this pulls the cross bar 58 towards the front side of the stove and this causes the plates 56 to slide over the inlets of the airwash passages 50 to fully or partially close off the airwash passageways 50. If the control lever 60 is pulled all the way out then the cover plates 56 completely shut off the airwash 50 to prevent any air being drawn in.

The stove also has a second air channel, referred to as a combustion air channel 70. The combustion air channel 70 is formed from a one-piece tube which is shown separately in Figure 11. While in this example the ceiling 11 of the chamber slopes, rising from the back of the chamber towards the front, it is also possible to provide a flat ceiling, in which case the channel 70 may have a different shape to conform to the shape of the ceiling. The tube of the combustion air channel 70 may be rigid and has portions 78, 80 extending along the ceiling, so the top heat-proof board forming the roof of the chamber 8 can be supported by the tube 70. In other embodiments the airwash baffle 52 could at least partially be supported on the tube 70.

As shown in Figures 6 and 11, the combustion air channel 70 has a pair of air inlets 72 at either end of the tube for drawing in air from outside the chamber. Each air inlet 72 is provided at one of the left and right sides of the chamber in the base of the stove (see the view of the underside of the stove in Figure 6 showing the inlets 72). The air from each air inlet 72 is passed via a firebed portion 74 of the combustion air channel 70 which passes along the fire bed, just below the grate 12, with each of the two fire bed portions 74 running along opposite sides of the chamber. The air inlets 72 are provided towards the front of the chamber and the fire bed portions 74 run back to the back wall of the chamber and then around bends 75 to respective rising portions 76 which extend upwards in the back left and back right corners of the chamber (the corners where the left and right side walls meet the back wall). Each of the rising portions 76 rises up to the point where the left and right side walls of the chamber meet the ceiling 11. Further bent portions 77 join the rising portions 76 to ceiling portions 78 which extend forwards from the back of the chamber towards the front side along the ceiling 11. The ceiling portions 78 extend along the sides of the chamber in the corners where the ceiling 11 meets the left and right side walls. The ceiling portions 78 extend forwards to a part of the ceiling above the grate 12. Further bends 79 link the two ceiling portions 78 to an intermediate portion 80 which extends horizontally between the ends of each ceiling portion 78 to link the two sides of the channel together. As shown in Figure 12, a number of combustion air outlets 82 are formed in the intermediate portion 80 so that air drawn in via both halves of the combustion air channel 70 is injected into the chamber from the ceiling. As shown in Figure 12, the combustion air outlets 82 are formed at different points around the perimeter of the intermediate portion 80 of the tube so as to inject the air into the chamber at different angles or orientations.

Hence, the air from the combustion air channels 70 takes a relatively indirect path to the point at which the air is injected into the chamber. The air is drawn in at the base of the stove near the front and then sent to the back of the chamber, up the back wall of the chamber and forward along the ceiling 11 before extending laterally over the ceiling towards the middle of the chamber where it is injected down from the ceiling into the chamber. The tube forming the channel 70 may be made from a heat-conductive material such as metal, so that the air in the tube is heated due to the heat of the fire and the accumulation of hot gases around the tube. As shown in Figure 4, the combustion products 42 from the burning fuel 40 will tend to gather near the ceiling and so the air from the combustion air channel 70 is injected directly into the region where the combustion products are gathering.

As shown in Figure 4, the intermediate part 80 of the combustion air channel protrudes out from the ceiling 11, so that combustion products 42 flowing along the ceiling are pushed downwards as they wash over the intermediate part 80 of the tube. This causes turbulent flow of the combustion gases over the tube which helps to mix the combustion products with the air being injected by the combustion air channel 70 to improve the efficiency with which the combustion gases are burnt. Since the air has travelled on a relatively long path through the chamber, along the fire bed where the fire is burning, up around the back of the chamber and along the ceiling, with the ceiling being particularly hot due to the accumulation of hot combustion gases, the air injected by the combustion air channel 70 is hot enough to support complete combustion of the combustion products 42. Also, the provision of air holes 82 in the intermediate part 80 of the channel at different angular positions around the tube circumference it means that air is injected at different orientations into the chamber which further promotes mixing of the combustion gases with the injected oxygen to improve combustion.

As shown in Figure 4, to encourage trapping of the combustion products near the outlets of the combustion air channel 70, a barrier 90 is formed in the ceiling of the chamber 8 between the gas outlet hole 30 and the outlet of the combustion air channel 70. For example, a lip may be formed in the ceiling which extends across the ceiling parallel to the front side of the chamber, between the gas outlet hole 30 and the intermediate part 80 of the channel 70. The barrier 90 makes it harder for the combustion products 42 to escape through the gas outlet hole 30 before they have been fully combusted.

As shown in Figures 4 and 6, a combustion air control 100 is provided for closing off the air supply from the combustion air channel 70 in a similar way to the airwash control 54. The combustion air control 100 includes a pair of closure plates 102, a crossbar 104 and a control lever 106. When the user pulls the control lever 106, the crossbar is drawn forwards and this causes the plates 102 attached to the crossbar 104 to slide over the air inlet 72 of the combustion air channel 70 to close off the air supply. It will be appreciated that the mechanisms shown for the airwash control 54 and combustion air control 100 are just one example. Other techniques could be used to control the amount of air provided by the channels 50, 70. For example, butterfly valves could be located inside the airwash passages 50 and combustion air channel 70, which can be opened or closed to vary the amount of air provided.

As shown in Figure 5, the parts of the combustion air channel 70 which extend along the sides of the chamber are at least partially inset into the walls of the chamber. For example, the firebed portion 74 on either side of the channel may extend underneath the bottom of the heatproof boards forming the left and right side walls 10 of the chamber, and the rising portion 76 may extend upwards between the back end of the side walls and the front of the rear wall, so that the channel 70 is at least partially hidden from view. This can make the stove more aesthetically pleasing and increases the effective width of the chamber 8 for a given width of stove 2, and also makes the stove easier to manufacture since by gripping the channel 70 between the heat boards forming the walls of the chamber, it is not necessary to provide other structural support for the channel. An alterative would be to have the channel jutting out from the side walls and this would increase the amount of heating of the air passing through the channels which may improve combustion, in which case some brackets or other form of support may be provided to hold the channel out from the side walls.

In use, the fuel 40 is loaded into the chamber 8 and placed on the grate 12. The fuel is lit and starts to char. Initially, both the airwash channel 50 and the combustion air channel 70 are fully open with the control levers 60, 106 pushed all the way in to allow the full amount of air to be provided by the airwash 50 and combustion air channel 70. The airwash is useful while the fire is heating up because at this point the fire is not yet hot enough to permit combustion of the combustion products 42 and so by providing air using the airwash 50 which washes down over the inside of the viewing window 24, the viewing window 24 can be kept clean. As the fire burns, it burns off some of the oxygen in the air within the chamber 8 and this causes the pressure in the chamber 8 to be lower than outside the stove, causing air to be drawn in from outside.

In conventional stoves, the airwash 50 would remain open once the fire is up to temperature and burning fully. One would expect that the airwash is required to keep the glass of the viewing window 24 clean. However, the inventors recognised that this leads to inefficient combustion of the combustion products 42 because the air drawn in through the airwash 50 eddies off the viewing window 24 into the chamber and tends to wash the combustion gases 42 straight up the gas outlet hole 30 without fully being combusted. Also, the air from the airwash is relatively cold since it has travelled up through the front corners of the housing outside the chamber, which are relatively cold compared to the chamber walls, and the air has passed along the viewing window which is also relatively cold, and so the airwash air is not hot enough to support efficient combustion of the combustion products 42.

The airwash 50 can be shut off by pulling out the airwash control lever 60 to cause the plates 56 to slide over the inlets to the airwash channels 50, once the fire is up to temperature and burning well. At this point, the combustion air channel 70 becomes the main source of oxygen for supporting the fire and this is injected directly into the region of the chamber near the ceiling where the combustion gases 42 gather. Since the air has travelled through a relatively long path through the fire bed, up the back of the chamber, and forwards along the ceiling before travelling into the centre of the chamber to the air outlet 82, the air is preheated to a relatively high temperature, enabling complete combustion of the combustion products. This means that the soot and tar and other dirty residue within the combustion products 42 is burnt off and so will not settle on the viewing window 24, avoiding the need for the airwash 50 to be kept open.

Eventually, the fire may die down once the fuel is used up, or if the user wishes to shut off the fire earlier then they can shut the combustion air control 100 to starve the fire of oxygen.

The combustion channel 70 can be made large enough to provide sufficient air to support a given size of fire. For example, for a 4.8 kW fire, the tube forming the channel 70 may have a diameter of at least 20 millimetres (providing a total cross sectional area at both inlets 72 of at least approximately 2500 square millimetres). It will be appreciated that for fires with different power ratings the size of the combustion air channel 70 may be smaller or larger. Also, while Figure 11 shows an example where the combustion air channel 70 has a circular cross-section, non-circular cross-sections such as an ellipse or a rectangle could also be used.

In summary, by using the combustion air channel 70 as the main source of air for the regular operation of the fire, rather than the airwash 50, surprisingly more efficient combustion can be achieved which results in cleaner smoke being output via the flue, cleaner ash gathering in the ashtray 14 and more energy being extracted from a given amount of fuel. This is contrary to the conventional wisdom that the airwash 50 is required to keep the viewing window 24 clean.

While Figure 11 shows one example of a possible path which the combustion air channel 70 may take through the chamber en route to the point at which the air is injected, other paths can also be used as shown in Figures 13A to 13D. In each of Figures 13A to 13D, the path of the combustion air channel 70 is shown in a side elevation in the left hand diagram, in a front elevation in the middle diagram and in plan view from above in the right hand diagram. Figure 13A shows for comparison the path taken by the tube shown in Figure 11. In this example the air inlets are formed near the front of the chamber and the tube has a firebed portions 74 which extend backwards near the base of the chamber through the firebed along the walls of the chamber, rising portions 76 which extend upwards at the back of the chamber along the walls to the left and right of the chamber, ceiling portions 78 which extend forwards again along the ceiling of the chamber from back to front and an intermediate portion 80 which extends laterally from left to right between the ceiling portion 78 on either side. The intermediate portion 80 includes the air outlets 82 for injecting air into the chamber from the ceiling.

Figure 13B shows another example of a path for the combustion air channel 70. Figure 133 is generally similar to Figure 13A, except that a serpentine portion 120 is provided at each side of the chamber where the channel 70 snakes backwards and forwards along the left and right walls of the chamber as it rises up to meet the ceiling portion 78.

Hence, rather than rising straight up at the back of the chamber as in Figure 13a, there are some additional bends in the channel which increase the length of the path taken by the air as it is guided up to the outlet 82. By increasing the length of the path taken by the air, the amount of heating is increased and so the air will be hotter at the point when it is injected into the chamber to improve combustion.

Figure 13C shows another example. This time, a single air inlet 72 is provided towards the back of the chamber at the base of the stove and a serpentine portion 122 then snakes left and right along the back wall of the chamber and rises up to meet the ceiling portion 78 which extends forwards from the back of the chamber along the ceiling of the chamber. Unlike in Figures 13A and 13B, the channel 70 of Figure 13C is a single ended channel which draws the air in at one end and outputs the air at the other end into the chamber. Hence, this time the part 122 extending laterally from left to right above the grate ends with an air outlet rather than connecting to part of the tube on the opposite wall. Again by providing a serpentine portion 122 with a number of bends snaking backwards and forwards, greater heating is achieved which increases the temperature of the injected air and improves the combustion efficiency of the combustion products.

Figure 13d shows another example. In this case, the tube is again a double ended tube with air inlets 72 at both ends at the front of the chamber to the left and right sides near the base of the stove. Again, there is a fire bed portion 74 which extends back through the fire bed just below the grate 12 and then there is a bend 75 and the air passes through a rising portion 76 which extends forwards diagonally towards the front of the chamber along the side walls and rises upwards to meet the ceiling. When the rising portion 76 meets the ceiling, it doubles backwards and a ceiling portion 78 extends back and forth along the ceiling in a serpentine path as shown in the right hand diagram of Figure 13D. The serpentine ceiling portion 78 links the two sides of the channel, and air outlet holes 82 are provided at various locations along the serpentine path 78 as it snakes back and forth along the ceiling.

As shown in Figures 13A to 13D there are a number of options for the path of the tube, but in general there may be at least one portion which extends along the ceiling 11 of the chamber in a direction towards or away from the front side of the chamber at which the viewing window 24 is located. By extending the air passageway forwards into the middle of the chamber along the ceiling, or from the front of the chamber backwards away from the viewing window, the distance travelled by the air is greater. This exploits the fact that the ceiling portion 78 of the combustion air channel 70 is where most heating of the combustion air will take place because this is where the hot gases rise to and so by increasing the length of the ceiling portion 78, better combustion can be achieved.

As shown in Figure 13A, in addition to having combustion air outlets 82 at the ceiling of the chamber, it is also possible to provide some further air outlets 130 lower down in the chamber. For example, as shown in Figure 13A, the further air holes 130 may be provided near the bottom of the rising portion 76 of the tube so that they inject air near the fire bed to enhance combustion of the fuel 40 itself Hence, there may be a number of air outlets in the combustion channel at different vertical levels within the chamber. Nevertheless, the main supply of air may be from the ceiling through the main air outlet 82. The other examples of Figures 13B, 130 and 130 could similarly be provided with further air outlets lower down the stove.

In general, to avoid resistance in the air flow through the combustion air channel 70, a total cross-sectional area of all the air outlet holes in the tube may be made equal to a total cross-sectional area of the inlet 72. As discussed above, by providing different outlets 82 at different orientations about the tube more mixing of the combustion gases can be achieved to improve combustion.

Figure 14 shows an alternative embodiment for forming a combustion air channel 70.

As shown in Figure 14, instead of extending up through the chamber, the combustion air channel 70 can be formed above the ceiling 11 of the chamber. The back of the housing 8 of the stove may have one more air inlet holes or slots 150 which draw air into a cavity 152 to the rear of the stove. Three parallel boards 154, 156, 158 extend outwards towards the front of the stove from the cavity 152. The boards may be made of metal or another heat-conducting material. The middle board 156 is shorter than the top and bottom boards 158 and the end of the top board 154 is bent down past the end of the middle board 156 to meet the bottom board 158. Hence, the boards form a passageway which extends from the cavity 152 towards the front of the chamber and then back towards the rear of the chamber along the ceiling 11. This passageway could extend throughout substantially the width of the stove from left to right (the direction into or out of the plane of the page as shown in Figure 14), or could be subdivided into a number of distinct passageways spaced across the width of the stove. A number of air outlets 82 are provided for injecting air in through the lower board 158 and into the chamber. Bolts or screws 160 hold the boards together. Hence, when the fire is burning, the low pressure in the chamber causes air to be drawn in through inlet 150 into the cavity 152. At this point the air from outside is relatively cold, but as it travels through the passageway 70, the combustion gases gathering just underneath the ceiling 11 formed by the lower board 158 heats the lower board 158 and the heat conductive material causes this heat to pass to the other boards and the passageway 70 and so the air gradually becomes hotter as it moves along the passageway until it reaches the air outlet 82 where the hot air is injected into the region comprising the combustion products. Otherwise the stove in this embodiment functions in a similar way to discussed above. Note that in this example the barrier 90 for trapping the combustion products behind the flue outlet hole 30 can be formed from the ends of the top and bottom boards 154, 158 forming the passageway 70, which may extend beyond the front wall of the passageway 70 to form a lip in the ceiling of the stove 2.

In the examples of Figures 13A to 13D, the combustion air channel 70 is a one-piece channel formed from a continuous tubular part. However, as shown in Figure 15 it is also possible to form the tube from a number of separate pieces 200 which may be joined together to form the combustion air channel. For example, the different parts may screw together or fit together by sliding a collar of one part 200 over a shoulder portion of another part 200 with the tight fit between the parts preventing air from escaping. In some cases making the channel out of multiple sections may make manufacturing easier or fitting of the channel in the chamber easier.

The combustion air channel 70 need not be rigid in all embodiments. For example in some cases the channel could be formed from a flexible hose which may be fed through the chamber and held in place by either sandwiching it between the boards 10 forming the walls of the chamber 8, or by providing hooks or brackets for holding the hose in place.

Also, as shown in Figure 16, in some cases the combustion channel may at least partially be formed by a frame of the chamber. For example, the chamber may include a metal frame 210 with hollow columns forming bottom left and back left edges of the chamber (and a similar frame to the right side of the stove). An air hole 212 in the base of the stove may draw in air through the inside of the frame towards the back of the chamber and up the rising portion 212 of the frame towards the ceiling. As shown in parts 1 and 2 of Figure 16, a tube portion 214 may then drop into a hole at the top of the frame (part 1) or alternatively sit over the open end of the frame with a hole in the tube as shown in part 2 of Figure 16, to receive the air drawn in through the frame. The tube portion 214 includes the ceiling portion 78 which extends forwards along the ceiling of the chamber and the intermediate portion 80 including the air holes for injecting air into the chamber. Hence, as shown in the bottom right part of Figure 16, the air may be passed in through a similar path to the one shown in Figure 11, but may reuse part of the frame of the chamber.

While the embodiment discussed above shows an example where a window is formed only in the front side of the chamber, in other examples is also possible to form additional windows in the left and right side walls of the stove to provide further visibility of the fire. In this case, additional airwash passageways 50 and baffles 52 may be provided for guiding air down the inside of the side windows.

While the examples shown above draw in air into the airwash passage 50 and the combustion air channel 70 at the base of the stove, in other examples the air inlets could be at a different part of the stove such as higher up the back of the stove. Also, in the examples above, the air is extracted from the vicinity of the stove in the room in which the stove is situated. However, it is also possible to connect the air inlets 50, 72 via a tube or hose to a location outside the building in which the stove is situated so that external air from the outside environment is drawn into the stove to avoid depleting the air in the room housing the stove. In such an embodiment, the air drawn in is likely to be even colder and so using the airwash as a main air supply would provide even lower efficiency. By heating the air through a relatively long combustion channel 70 before it is injected into the region near the ceiling of the chamber, combustion efficiency can be improved.

Figure 17 shows a method of burning fuel in the stove 2. At step 300, fuel is loaded into the chamber 8 and placed on the grate 12. At step 302 the fuel is lit. At step 304 the user shuts the door and ensures that the airwash 50 is fully open so that as much air as possible is provided for getting the fire started and a curtain of air is directed down the inside of the viewing window 24 to prevent the combustion products 42 from the fuel settling on the viewing window 24 before the fire is hot enough to burn off the combustion products. At step 306 the user determines whether the fire is up to temperature. For example, the user can see through the viewing window and determine from the appearance of the flames whether the fire is up to temperature. If the fire is not yet up to temperature then the user waits for it to heat up and the airwash remains open. Once the fire is up to temperature then at step 308 the user adjusts the airwash control 54 to reduce the amount of air provided by the airwash 50 to less than the amount of air provided by the combustion air channel 70. Preferably the airwash 50 is shut off entirely so that no air is provided by the airwash. Even without the airwash, the viewing window 24 does not become dirty because the preheated air provided by the channel 70 is sufficient to burn off the combustion products 42 to avoid dirtying the viewing window 24. Sometimes the user may wish to leave the airwash 50 slightly open to reduce the chance of the glass becoming dirty, so it is not essential to shut off the airwash altogether. Nevertheless by running the fire with the rear combustion air channel 70 providing the main source of oxygen for the fire, this avoids the combustion products 42 being washed up the chimney before they are fully burnt and enables more complete combustion. At step 310 the combustion products are burnt using the combustion air as the main supply. Wien the user wishes to turn off the fire, then the user can shut off both the airwash 50 and the combustion air channel 70 by closing both controls 54, 100. This starves the fire of oxygen and causes the fire to go out.

In the present application, the words "configured to..." are used to mean that an element of an apparatus has a configuration able to carry out the defined operation. In this context, a "configuration" means an arrangement or manner of interconnection of hardware or software. For example, the apparatus may have dedicated hardware which provides the defined operation, or a processor or other processing device may be programmed to perform the function. "Configured to" does not imply that the apparatus element needs to be changed in any way in order to provide the defined operation.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.

Claims

CLAIMS1. A stove for burning fuel, comprising: a chamber for receiving the fuel; a viewing window at a front side of the chamber; at least one airwash passage configured to pass air from outside the chamber along the inside of the viewing window; an airwash control configured to adjust an amount of air provided by said at least one airwash passage; and at least one combustion air channel configured to pass air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of said at least one airwash passage.
2. The stove according to claim 1, wherein at least one of said one or more combustion air outlets is configured to direct air into the chamber from the ceiling of the chamber.
3. The stove according to any of claims 1 and 2, comprising a gas outlet hole in the ceiling of the chamber; wherein at least one of said one or more combustion air outlets is positioned further from the front side than the gas outlet hole.
4. The stove according to claim 3, comprising a barrier on the ceiling of the chamber between said gas outlet hole and said at least one of said one or more combustion air outlets.
5. The stove according to any preceding claim, wherein said at least one combustion channel includes a protruding part which protrudes from the ceiling of the chamber.
6. The stove according to claim 5, wherein at least one of said one or more combustion air outlets is formed in the protruding part.
7. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a plurality of said combustion air outlets at different orientations relative to the chamber.
8. The stove according to claim 6, wherein a plurality of the combustion air outlets are formed at different points about the perimeter of the protruding part.
9. The stove according to any preceding claim, wherein said at least one combustion air channel comprises at least one bend.
10. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a serpentine portion configured to pass the air from outside the chamber along a serpentine path along or through the chamber to at least one of said one or more combustion air outlets.
11. The stove according to any preceding claim, wherein said at least one combustion air channel is configured to pass the air from outside the chamber to said at least one ceiling portion via a rising portion extending from a lower portion of the chamber towards the ceiling of the chamber.
12. The stove according to any preceding claim, wherein said at least one combustion air channel is configured to pass the air from outside the chamber to said at least one ceiling portion via a firebed portion extending along or below a firebed of the chamber.
13. The stove according to any preceding claim, wherein said at least one combustion air channel also comprises at least one further combustion air outlet at a lower part of the chamber than said one or more combustion air outlets.
14. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a tubular channel having air inlets at both ends for drawing in air from outside the chamber, and the one or more combustion air outlets are at an intermediate part of the channel between the air inlets.
15. The stove according to claim 14, wherein said at least one combustion air channel comprises at least two ceiling portions extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber, one ceiling portion on each side of the intermediate part.
16. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a one-piece channel.
17. The stove according to any of claims 1 to 15, wherein at least part of said at least one combustion air channel comprises a passageway within a frame of the chamber.
18. The stove according to any preceding claim, wherein said at least one combustion air channel provides structural support for another part of the stove.
19. The stove according to claim 18, wherein the other part of the stove comprises a roof of the chamber.
20. The stove according to any of claims 18 and 19, wherein the other part of the stove comprises an airwash baffle for guiding the air from the airwash passage down the inside of the viewing window.
21. The stove according to any preceding claim, comprising a door at the front side of the chamber, wherein the viewing window is formed in the door.
22. A method for burning fuel in a stove comprising a chamber for receiving the fuel, a viewing window at a front side of the chamber, at least one airwash passage configured to pass air from outside the chamber along the inside of the viewing window, and at least one combustion air channel configured to pass air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of said at least one airwash passage; the method comprising: lighting a fire in the chamber; passing air along the inside of the viewing window using the at least one airwash passage while the fire heats up; and when the fire is up to temperature, reducing an amount of air provided by the at least one airwash passage to less than an amount of air provided by the at least one combustion air channel.
23. A stove substantially as herein described with reference to the accompanying drawings.
24. A method substantially as herein described with reference to the accompanying drawings.Amendments to the claims have been de as follows:CLAIMS1. A stove for burning fuel, comprising: a chamber for receiving the fuel; a viewing window at a front side of the chamber; at least one airwash passage configured to pass air from outside the chamber along the inside of the viewing window; an airwash control configured to adjust an amount of air provided by said at least one airwash passage; and at least one combustion air channel configured to pass air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of said at least one airwash passage.2. The stove according to claim 1, wherein at least one of said one or more combustion air outlets is configured to direct air into the chamber from the ceiling of the chamber.3. The stove according to any of claims 1 and 2, comprising a gas outlet hole in the ceiling of the chamber; wherein at least one of said one or more combustion air outlets is positioned further from the front side than the gas outlet hole.4. The stove according to claim 3, comprising a barrier on the ceiling of the chamber between said gas outlet hole and said at least one of said one or more combustion air outlets.5. The stove according to any preceding claim, wherein said at least one combustion channel includes a protruding part which protrudes from the ceiling of the chamber.6. The stove according to claim 5, wherein at least one of said one or more combustion air outlets is formed in the protruding part.7. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a plurality of said combustion air outlets at different orientations relative to the chamber.8. The stove according to claim 6, wherein a plurality of the combustion air outlets are formed at different points about the perimeter of the protruding part.9. The stove according to any preceding claim, wherein said at least one combustion air channel comprises at least one bend.10. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a serpentine portion configured to pass the air from outside the chamber along a serpentine path along or through the chamber to at least one of said one or more combustion air outlets.11. The stove according to any preceding claim, wherein said at least one combustion air channel is configured to pass the air from outside the chamber to said at least one ceiling portion via a rising portion extending from a lower portion of the chamber towards the ceiling of the chamber.12. The stove according to any preceding claim, wherein said at least one combustion air channel is configured to pass the air from outside the chamber to said at least one ceiling portion via a firebed portion extending along or below a firebed of the chamber.13. The stove according to any preceding claim, wherein said at least one combustion air channel also comprises at least one further combustion air outlet at a lower part of the chamber than said one or more combustion air outlets.14. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a tubular channel having air inlets at both ends for drawing in air from outside the chamber, and the one or more combustion air outlets are at an intermediate part of the channel between the air inlets.15. The stove according to claim 14, wherein said at least one combustion air channel comprises at least two ceiling portions extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber, one ceiling portion on each side of the intermediate part.16. The stove according to any preceding claim, wherein said at least one combustion air channel comprises a one-piece channel.17. The stove according to any of claims 1 to 15; wherein at least part of said at least one combustion air channel comprises a passageway within a frame of the chamber.18. The stove according to any preceding claim, wherein said at least one combustion air channel provides structural support for a roof of the chamber or an airwash baffle for guiding the air from the airwash passage down the inside of the viewing window.19. The stove according to any preceding claim, comprising a door at the front side of the chamber, wherein the viewing window is formed in the door.20. A method for burning fuel in a stove comprising a chamber for receiving the fuel, a viewing window at a front side of the chamber, at least one airwash passage configured to pass air from outside the chamber along the inside of the viewing window, and at least one combustion air channel configured to pass air from outside the chamber via at least one ceiling portion extending along a ceiling of the chamber in a direction towards or away from the front side of the chamber to one or more combustion air outlets at a position further from the front side than an outlet of said at least one airwash passage; the method comprising: lighting a fire in the chamber; passing air along the inside of the viewing window using the at least one airwash passage while the fire heats up; and when the fire is up to temperature, reducing an amount of air provided by the at least one airwash passage to less than an amount of air provided by the at least one combustion air channel.21. A stove substantially as herein described with reference to the accompanying drawings.22. A method substantially as herein described with reference to the accompanying drawings.