GB2432657A

GB2432657A - Stoves

Info

Publication number: GB2432657A
Application number: GB0623476A
Authority: GB
Inventors: Gareth Hunt; Peter Rogers
Original assignee: AGA Consumer Products Ltd
Current assignee: AGA Consumer Products Ltd
Priority date: 2005-11-26
Filing date: 2006-11-27
Publication date: 2007-05-30
Also published as: GB0623476D0; GB0524238D0

Abstract

A stove 100 comprises, in combination, a cooker 4 and a boiler 3 for heating water. The stove comprises a boiler burner 1 for the boiler and a cooker burner 2 for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that they burn fuel to produce combustion gases. The boiler further comprises a heat exchanger (11, fig.4) arranged such that the combustion gases from both burners can flow through the heat exchanger in order to extract heat from the combustion gases to heat water. A heat exchanger (8, fig.4) comprises first and second heat exchanger units (10 and 11, fig.4), arranged such that the combustion gases from the boiler burner pass through the first and second units sequentially, where the second heat exchanger unit is a condensing heat exchanger. The stove comprises an exhaust fan (30, fig.9) arranged to suck the combustion gases out of the stove and a control unit 32 which is arranged to control the speed of the exhaust fan in order to control the level of combustion in at least one of the burners. The stove also comprises a common flue (28, fig.2) for removal from the stove of the combustion gases from both the boiler and cooker burners. The flue pipe has a diameter of less than 75mm, typically 54mm, and may be made from stainless steel tube. Furthermore, the stove comprises a hotplate 7, ovens 5 and 6, and a cooker burner arranged to burn fuel to produce combustion gases, in which the combustion gas flow path diverges at the hotplate such that only a part of the combustion cases directly pass the hotplate, the remainder passing directly to the ovens. Preferably, the burners burn a liquid fuel, such as oil.

Description

STOVES

This invention relates to stoves, particularly (but not exclusively) to those comprising in combination a cooker and a boiler for hot water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable.

Such stoves conveniently provide both hot water for central heating, washing and so on and also means for cooking, such as ovens or hotplates. An example of such a stove can be seen in UK Patent Application publication number 2 280 747.

According to a first aspect of the invention, there is provided a stove comprising in combination a cooker and a boiler for heating water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that, in use, they burn fuel to produce combustion gasses, the boiler further comprising a heat exchanger arranged such that the combustion gasses from both burners can flow through the heat exchanger, in use, in order to extract heat from the combustion gasses to heat water.

Whilst it is accepted that combustion gasses from a boiler burner be used to heat water in a heat exchanger -indeed that is the generally accepted method of heating water in a boiler -we have appreciated that some usable heat remains in the combustion gasses from the cooker burner even after they have heated the cooker. A stove as provided by this aspect of the invention can therefore make more efficient use of the heat energy in the combustion gasses produced by its cooker burner. A common exit may be provided from the stove for combustion gasses from each burner.

The heat exchanger may comprise first and second heat exchanger units, arranged such that combustion gasses from the boiler burner pass, in use, through first and second units sequentially. The second unit is preferably a condensing heat exchanger unit, where, in use, the combustion gasses passing therethrough are cooled to the point where water vapour in the combustion gasses condenses. Preferably, the cooker burner and the heat exchanger are arranged such that, in use, cooking gasses from the cooker burner enter the heat exchanger between the first and second heat exchanger units and flow through the second unit.

This has been found to be particularly efficient as additional heat energy can be recovered from the combustion gasses; once the combustion gasses have heated the cooker (as is the case in the most preferred embodiment), they will have lost some heat and therefore be at comparable temperature to the boiler combustion gasses exiting the first unit. The first unit may therefore, in use, take combustion gasses from the boiler burner only and may cool those gasses to a temperature comparable to the combustion gasses from the cooker burner, whereas the second Unit may take, in use, combustion gasses from either burner. This temperature is likely to be in the region where the second unit being a condensing heat exchanger is particularly useful, as the second heat exchanger could then condense the moisture out of the combustion gasses.

In order to achieve this, the stove may comprise a burner gas flow path for combustion gasses from the boiler burner sequentially through the first unit, the second unit and then to an exit and a cooker gas flow path for combustion gasses from the cooker burner past the cooker and into the first flow path at a junction between the first and second units. The boiler and cooker gas flow paths may be in common through the second unit and to the exit. Most preferably, the cooker gas flow path does not pass through the first unit.

The gas flow paths may be defined by voids within the stove. The cooker gas flow path preferably passes adjacent to those parts of the cooker are to be heated; typically this is around at least one of a cooking surface, such as a hob, and an oven. As is well known, this leads to heating of the relevant parts.

The junction may be arranged so as to resist, in use, combustion gasses from the boiler burner passing back along the cooker gas flow path. This would be undesirable, as this would lead to combustion gasses passing back through the cooker and possibly out of the stove otherwise than through the exit. The junction may therefore comprise an anti-flowback device, which is arranged to use flow of boiler combustion gasses to suck gasses from the cooker gas flow path.

Preferably, the anti-flowback device is arranged to use the Bernoulli or Venturi effects, typically by having, in use, the boiler combustion gasses flow over an orifice separating the cooker gas flow path from the boiler gas flow path, thereby reducing the pressure in the cooker gas flow path adjacent to the junction. The junction may therefore comprise a pipe forming part of the cooker gas flow path projecting into the boiler gas flow path and having an orifice on the side thereof that faces away from, the direction in which combustion gasses flow, in use, through the boiler gas flow path. Preferably, the side of the pipe facing the flow, in use, of combustion gasses in the boiler gas flow path is substantially free of orifices.

This provides a simple way of preventing unwanted boiler combustion gasses flowing into the cooker gas flow path; when boiler combustion gasses are flowing they will cause a drop in pressure in the cooker gas flow path and hence cause gas to be drawn out of the cooker gas flow path, not inwards. This will be the case even if no combustion gasses are flowing in the cooker gas flow path.

The first and second heat exchanger units may share a common wall.

This allows for a much more compact heat exchanger -rather than comprising a series of sequentially mounted discrete units, the heat exchanger may comprise one monolithic body. Furthermore, sharing a wall between the two units may improve efficiency, as the heat that would otherwise be lost through that wall can be passed within the two units; the external surface area of the heat exchanger is reduced, thereby reducing the area through which heat can be lost.

According to a second aspect of the invention, there is provided a stove comprising in combination a cooker and a boiler for hot water, the stove comprising a boiler burner for the boiler and a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that, in use, they burn fuel to produce combustion gasses, further comprising an exhaust fan arranged to, in use, suck the combustion gasses out of the stove and a control unit which is arranged to control, in use, the speed of the exhaust fan in order to control the level of combustion in at least one of the burners.

We have therefore appreciated that the level of combustion from the burners can be controlled by controlling the flow of combustion gasses out of the stove. This provides simple control method, and can result in improved accuracy of control of the level of combustion. Preferably, the control unit is arranged to control the level of combustion to achieve a desired heat output of the relevant burner and/or to maintain substantially optimum combustion efficiency at the relevant burner.

The control unit may be arranged to provide a closed-loop control of the level of combustion at the burner, in use. The control unit may therefore be arranged to estimate or determine an actual level of combustion, typically using a measured parameter such as the level of oxygen in the combustion gasses, and compare this to a desired level of combustion.

Indeed, the stove may further comprise an oxygen sensor to determine the level or concentration of oxygen in the combustion gasses. The control unit may be arranged so as to use the determined oxygen level when controlling the level of combustion in the stove. The oxygen concentration can be used as feedback on the level of combustion in the stove, thereby adding to the accuracy with which the combustion level is set.

The stove may further provide an intake fan arranged to, in use, suck air into the stove and provide it to at least one of the burners; the control unit may be arranged to control, in use, the speed of the air intake fan in order to control the level of combustion in the stove. By controlling both air intake and the removal of combustion gasses, more precise control over the level of combustion can be achieved.

The stove preferably comprises a flue, arranged to convey the combustion gasses from both boiler and cooker burners away from the stove once they have been used to heat the appropriate part of the stove. The exhaust fan may be provided at, or at least closer to, the distal end of the flue. The flue may comprise, in the preferred embodiment, a pipe of diameter less than 60mm, and most preferably 54mm in diameter, which is much smaller than is possible with prior art stoves of the kind set forth.

The control unit may be arranged to control the speed of the exhaust fan dependent upon the movement of air around the exhaust fan outside the flue. This is most useful where winds or similar may be blowing outside of a building where the stove is installed, as such winds may otherwise have an effect on the combustion levels within the stove.

Such a stove conveniently falls within the first aspect of the invention, especially where there is provided a second heat exchanger unit, typically a condensing heat exchanger unit, through which combustion gasses from both cooker and boiler burners pass. By doing so, the combustion gasses can be cooled to such a degree that plastic material impeller blades can be used in the exhaust fan; otherwise the combustion gasses could be too hot for plastic material blades to handle.

The control unit may be arranged to fire either of the burners in a modulated manner, depending upon the desired heat output. This desired heat output may be based on the demand from the boiler or cooker.

Typically, the burner output may be modulated by varying the amount of fuel provided to the burner for combustion. Fine control may then be achieved by modulating the speed of the air intake and/or exhaust fans.

This is particularly advantageously used with the closed-loop control discussed above to provide efficiently controlled combustion.

Accordingly, the control unit may be arranged to regulate the heat output by one or other of the burners in up to three ways: firstly, by modulating the firing of the burner; secondly, by controlling the amount of air taken into the stove and supplied to the burner; and thirdly, by controlling the speed at which combustion gasses are sucked out of the stove.

Preferably, the effect on level of combustion of controlling the level of combustion is greater than that of controlling the exhaust gas speed; this allows the third way to be used as a "fine control" over the level of combustion.

The stove may further comprise a water trap, arranged to collect water condensed from the combustion gasses in the second heat exchanger unit.

The flue may also comprise a drain for condensed water vapour to drain such water vapour to the water trap.

According to a third aspect of the invention, there is provided a stove comprising a hotplate and an oven, and a cooker burner arranged to burn fuel to produce combustion gasses to heat the hotplate and the oven, the stove defining a cooker gas flow path for combustion gasses from the cooker burner, past the hotplate and the oven to heat the hotplate and the oven and then to an exit, in which the flow path diverges at the hotplate such that, in use, only a part of the combustion gasses from the cooker burner directly pass the hotplate, the remainder passing directly to the oven.

As the hotplate has been found not to require the same amount of heating as an oven does, it is more efficient to provide a fraction of the combustion gasses to the hotplate as otherwise it could be heated to an unnecessarily high temperature.

The flow path may recombine after passing the hotplate; this would allow the combustion gasses which have passed over the hotplate to continue to the oven where they may be able to pass further heat to the oven.

The flow path may pass over three sides of the oven, typically top, bottom and side for a generally cuboid oven, before passing to an exit from a cooker part of the stove. The greater distance the combustion gasses can flow over the oven, the greater amount of heat the gasses can pass to the oven. The stove may comprise a further oven, around only one side of which the flow path passes. This can therefore provide a cooler oven than the (main) oven. The part of the flow path which passes the further oven may be the same part as passes the third of the three sides of the oven. This leads to a cooler further oven.

The flow path may comprise a baffle at the point where the flow path diverges. The baffle may be arranged to direct, in use, combustion gasses in two directions, which may be towards the hotplate and towards the oven.

According to a fourth aspect of the invention, there is provided a stove comprising in combination a cooker and a boiler for hot water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, the stove further comprising a heat exchanger arranged such that combustion gasses from the boiler burner flow, in use, in order to extract heat from the combustion gasses, in which the heat exchanger comprises first and second heat exchanger units, arranged such that combustion gasses from the from the boiler burner pass, in use, through first and second units sequentially, the second unit being a condensing heat exchanger unit, wherein, in use, the combustion gasses passing therethrough are cooled to the point where water vapour in the combustion gasses condenses and wherein the first and second heat exchanger units may share a common wall.

Such an oven has the advantages previously recited as regards sharing a wall between heat exchanger units. Preferably, the stove is one according to the first, or second or third, aspects of the invention, and may have any of the optional features of the preceding aspects.

According to a fifth aspect of the invention, there is provided a stove comprising in combination a cooker and a boiler for heating water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that, in use, they burn fuel to produce combustion gasses, further comprising a common flue for removal from the stove of the combustion gasses from both boiler and cooker burners, in which the flue comprises a pipe extending from the stove, having a diameter of less than 75mm.

We have appreciated that use of a small-bore flue pipe in a stove of the kind set forth is possible. More particularly, the diameter is less than 60mm, and may be about 54mm.

The use of a small bore pipe as described can be made possible for a number of reasons. The stove may be one according to the first aspect of the invention, where there is provided a second heat exchanger unit, typically a condensing heat exchanger unit, through which combustion gasses from both cooker and boiler burners pass. This cools the combustion gasses to a degree where they may safely be handled in a small pipe. Alternatively, or in addition, the stove may be one according to the third aspect of the invention, where the combustion gasses are pulled out of the stove by means of a fan. As the flow of combustion gasses is forced, a smaller pipe may be used.

There now follows, by way of example only, an embodiment of the present invention, described with reference to the accompanying drawings, in which: Figure 1 shows a cross section view through a stove according to a first aspect of the invention, from the front of the stove; Figure 2 shows a cross section view of the stove of Figure 1, from the rear of the stove; Figure 3 shows a plan view cross section of the heat exchanger of the stove of Figure 1; Figure 4 shows a cross section through the heat exchanger of the Figure 3 along line C-C; Figure 5 shows a view of the junction between flow paths between heat exchanger units of the stove of Figure 1; Figure 6 shows a cross section of the heat exchanger of Figure 3 along line A-A; Figure 7 shows a cross section of the heat exchanger of Figure 3 along line B-B; Figure 8 shows a further plan view cross section of the heat exchanger of Figure 3; and Figure 9 shows a schematic view of the stove of Figure 1 with a flue pipe connected to vent spent combustion gasses through an external wall.

The stove 100 shown in the accompanying drawings comprises a boiler burner 1 and a cooker burner 2. These are independently controllable and each burn a liquid fuel -in this embodiment oil -in order to generate hot combustion gasses. The boiler burner 1 is arranged to heat, using its combustion gasses, a boiler depicted generally at 3 whilst the cooker heats, using its combustion gasses a cooker generally depicted at 4. The boiler thereby heats water for use in heating and general domestic use, whilst the cooker 4 comprises first, roasting oven 5, second, simmering oven 6 and a hotplate 7 all heated by the cooker burner 2.

The boiler 3 comprises a heat exchanger 8 best seen in Figure 2 and 4.

The heat exchanger 8 takes the combustion gasses from boiler burner 1 and passes them through generally serpentine passageways around passing through but isolated from a water jacket 12. Accordingly, heat in the combustion gasses can be passed to the water in the jacket 12.

The boiler burner 2 is mounted in a combustion chamber 9. The boiler burner is mounted above a first heat exchanger unit 10 forming part of the heat exchanger 8. This unit 10 comprises a plurality of horizontal baffles, stacked vertically and offset from one another horizontally in an alternating fashion so as to define a back-and-forth flow path, generally downwards, for the combustion gasses. The flow path through this unit runs from the combustion chamber 9 to a junction box 13 situated at the bottom of the heat exchanger 8. Two sets of baffles ha, lib (Figure 3) are provided, which provide parallel flow paths through the water jacket 12. The first heat exchanger unit 10 provides a first-pass cooling of the combustion gasses; the gasses flow through this first heat exchanger as shown by the arrows in Figure 4.

The heat exchanger 8 also comprises a second, condensing heat exchanger unit 11 through which the combustion gasses flow once they have passed through the first heat exchange unit. The second heat exchanger comprises a plurality of vertical parallel pipes 14 passing through the water jacket 12 such that sufficient heat is removed from the combustion gasses that water vapour in the combustion gasses condenses from the gasses; this allows the latent heat of evaporation to be transferred to the water in the jacket 12 thereby increasing the amount of energy transferred to the water. The pipes therefore define a flow path for combustion gasses upwards from the junction box 13 to a flue exit 15. Water vapour condensed from the combustion gasses flows down the inside of the pipes 14 and is collected in the junction box 13, which acts as a water trap.

The cooker burner 2 is situated in its own combustion chamber 16.

Combustion gasses from this burner rise naturally through convection towards the hotplate 7. A baffle 17 divides the flow of combustion gasses (depicted by arrows in Figure 1) such that some then flow over hotplate 7, thereby heating it, whilst others pass directly to a passage 18 directly adjacent to the top side 19 of roasting oven 5, which the gasses passing the hotplate rejoin. By ensuring that only a fraction of the combustion gasses impinge directly on the hotplate 7, the temperature of the hotplate 7 in use can be controlled, therefore allowing for more accurate and hence efficient use of fuel.

The passage 18 carries on around three sides of the (generally cuboid) roasting oven 5: top 19, side 20 and bottom 21; combustion gasses passing through the passage 18 therefore heat the roasting oven. As the passage 18 passes the third, bottom side 21 of the roasting oven 5, it is also directly adjacent to the top side 22 of the simmering oven 6; combustion gasses passing through the passage 18 therefore also heat the simmering oven 6 but to a lesser extent than the roasting oven as, firstly, they cover less area of the simmering oven and, secondly, the combustion gasses will have lost heat to the roasting oven 5 by the time they reach the simmering oven 6.

The passage 18 terminates in a port 23 through which the combustion gasses pass. This is connected to a pipe 24 (Figure 2), which takes the combustion gasses to the junction box 13. The combustion gasses from the cooker burner therefore pass to the second heat exchanger unit 11 and heat in addition to that provided to the cooker 4 can be extracted therefrom. This heat would otherwise have been wasted by being passed out of a flue.

Accordingly, there exists a first flow path for combustion gasses from the boiler burner 1, through the first heat exchanger unit 10, junction box 13 and second heat exchanger unit 11. A second flow path exists from the cooker burner 2 through passage 18 and pipe 24 to the junction box 13, whereupon combustion gasses flow along the remainder of the first flow path.

The junction box can be seen in most detail in Figure 5 of the accompanying drawings. In order to prevent combustion gasses flowing back from the boiler burner 1 into the cooker 4 through pipe 24 and the second flow path particularly when the cooker burner 2 is not in operation, the pipe 24 terminates in the junction box 13 by means of a Venturi Effect device 25.

This comprises au orifice 26 in the side of the pipe facing away from the flow of boiler combustion gasses from the first heat exchanger unit 10 to the second heat exchanger unit 11. As boiler combustion gasses 27 pass over the Venturi Effect device 25, the flow of gasses over the orifice 26 causes a drop in pressure around the orifice, in accordance with the Venturi and Bernoulli effects. Rather than permitting boiler gasses to flow back up pipe 24, this causes gasses -be they combustion gasses or simply air -to be drawn from pipe 24 and hence the cooker 4.

Once the combustion gasses from both of the boiler 1 and cooker burners 2 have passed through the heat exchanger 8, they pass to a flue pipe 28. This is a 54mm (outside diameter) stainless steel tube.

As can be seen in Figure 9 of the accompanying drawings, the flue pipe 28 passes from the stove 100 through an external wall 101 to vent spent combustion gasses to the outside of the building in which the stove 100 is situated. At the distal end of the flue pipe 28 there is provided a exhaust fan 30 (shown schematically in Figure 9) which acts to suck Out the spent combustion products from the stove 100.

The roasting oven is also provided with an outlet 37 for cooking fumes; this runs via pipe 38 to flue pipe 28 to vent such fumes outside.

The boiler 3 is provided with an air intake fan 31, which sucks in air from outside the stove 100 to provide boiler 1 and cooker 2 burners with air for combustion. A control unit 32 controls both the speed of the air intake fan 31 and the exhaust fan 30 in order to control the level of combustion in the burners 1, 2. Whilst the level of fuel supplied to the burners can act as a rough adjustment to the level of combustion, for most efficient and accurately controlled combustion, we have found that a combination of controlling the air taken into a stove and the speed at which spent combustion products are sucked out of the stove 100 acts to provide such control. Indeed, the level of fuel supplied to the burners 1, 2 can act as a first level of control, the air intake fan speed a more accurate level of control and the exhaust fan speed a final and particularly accurate or "trim" control.

Furthermore, the control unit 32 bases its control of the combustion levels at the burners 1,2 by sampling the oxygen levels in the exit 15 of the heat exchanger 8. It does this using an oxygen sensor 33 in the exit 15. The oxygen levels in the flue gasses indicates how complete combustion is in the burners; if not enough oxygen is present, then combustion is likely to be incomplete, which results in less efficient use of fuel.

In addition, the provision of exhaust fan allows the stove to respond to gusts of wind and the like blowing over or into the end of flue pipe 28.

Without such a speed-controlled fan 30, such gusts change the back-pressure on the system and can have an effect on the combustion rate. In severe cases the burners could even be extinguished.

The fan 30 and flue pipe 28 are further provided with a drain 28 for liquids condensing out of the flue; this is connected to the water trap in the stove 100.

Figures 3 and 6 to 8 show the flow of water through the jacket 12.

Figure 3 shows a cross section horizontally through the heat exchanger 8 through the vertical middle of the heat exchanger, whereas Figure 8 shows a similar cross section towards the top.

Water initially flows into the top of the heat exchanger 8 water jacket 12 through inlet 35. The water then flows around (Figure 3 and 6) the pipes 14 of the second heat exchanger unit 11; the coldest water is used to do this as, to remove the last remaining heat from the combustion gasses a larger temperature difference is desirable. The water next flows between (Figures 3 and 7) and around (Figures 3 and 6) the the baffle sets ha, llb of the first heat exchanger unit 11. Finally, the water flows across the top of the first heat exchanger unit 11 (Figure 8) and out of outlet 36 to heat radiators and to be supplied to baths, sinks and the like.

Claims

CLAIMS

1. A stove comprising in combination a cooker and a boiler for heating water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that, in use, they burn fuel to produce combustion gasses, the boiler further comprising a heat exchanger arranged such that the combustion gasses from both burners can flow through the heat exchanger, in use, in order to extract heat from the combustion gasses to heat water.

2. The stove of claim 1 in which a common exit is provided from the stove for combustion gasses from each burner.

3. The stove of claim 1 or claim 2, in which the heat exchanger comprises first and second heat exchanger units, arranged such that combustion gasses from the boiler burner pass, in use, through first and second units sequentially.

4. The stove of claim 3 in which the second unit is a condensing heat exchanger unit, where, in use, the combustion gasses passing therethrough are cooled to the point where water vapour in the combustion gasses condenses.

5. The stove of claim 4 in which the cooker burner and the heat exchanger are arranged such that, in use, cooking gasses from the cooker burner enter the heat exchanger between the first and second heat exchanger units and flow through the second unit.

6. The stove of any of claims 3 to 5 in which the first unit, in use, takes combustion gasses from the boiler burner only and may cool those gasses to a temperature comparable to the combustion gasses from the cooker burner.

7. The stove of any of claims 3 to 6 in which the second unit takes, in use, combustion gasses from either burner.

8. The stove of any of claims 3 to 7 in which the stove comprises a burner gas flow path for combustion gasses from the boiler burner sequentially through the first unit, the second unit and then to an exit and a cooker gas flow path for combustion gasses from the cooker burner past the cooker and into the first flow path at a junction between the first and second units.

9. The stove of claim 8 in which the boiler and cooker gas flow paths are in common through the second unit and to the exit.

10. The stove of claim 8 or claim 9 in which the cooker gas flow path passes adjacent to those parts of the cooker are to be heated.

11. The stove of claim 10 in which the parts of the cooker that are to be heated comprise at least one of a cooking surface, such as a hob, and an oven.

12. The stove of any of claims 8 to 11 in which the junction is arranged so as to resist, in use, combustion gasses from the boiler burner passing back along the cooker gas flow path.

13. The stove of claim 12 in which the junction comprises an anti-flowback device, which is arranged to use flow of boiler combustion gasses to suck gasses from the cooker gas flow path.

14. The stove of claim 13 in which the anti-flowback device is arranged to use the Bernoulli or Venturi effects.

15. The stove of claim 13 or claim 14 in which the anti-flowback device is arranged such that, in use, the boiler combustion gasses flow over an orifice separating the cooker gas flow path from the boiler gas flow path, thereby reducing the pressure in the cooker gas flow path adjacent to the junction.

16. The stove of any of claims 12 to 15 in which the junction comprises a pipe forming part of the cooker gas flow path projecting into the boiler gas flow path and having an orifice on the side thereof that faces away from, the direction in which combustion gasses flow, in use, through the boiler gas flow path.

17. The stove of claim 16 in which the side of the pipe facing the flow, in use, of combustion gasses in the boiler gas flow path is substantially free of orifices.

18. The stove of any of claims 3 to 17 in which the first and second heat exchanger units share a common wall.

19. The stove of claim 18 in which the heat exchanger comprises one monolithic body.

20. A stove comprising in combination a cooker and a boiler for hot water, the stove comprising a boiler burner for the boiler and a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that, in use, they burn fuel to produce combustion gasses, further comprising an exhaust fan arranged to, in use, suck the combustion gasses out of the stove and a control unit which is arranged to control, in use, the speed of the exhaust fan in order to control the level of combustion in at least one of the burners.

21. The stove of claim 20 in which the control unit is arranged to control the level of combustion to achieve a desired heat output of the relevant burner and/or to maintain substantially optimum combustion efficiency at the relevant burner.

22. The stove of claim 20 or claim 21 in which the control unit is arranged to provide a closed-loop control of the level of combustion at the burner, in use.

23. The stove of any of claims 20 to 22 in which the control unit is arranged to estimate or determine an actual level of combustion, typically using a measured parameter such as the level of oxygen in the combustion gasses, and compare this to a desired level of combustion.

24. The stove of any of claims 20 to 23 in which the stove further comprises an oxygen sensor to determine the level or concentration of oxygen in the combustion gasses.

25. The stove of any of claims 20 to 24 which further comprises an intake fan arranged to, in use, suck air into the stove and provide it to at least one of the burners.

26. The stove of claim 25 in which the control unit is arranged to control, in use, the speed of the air intake fan in order to control the level of combustion in the stove.

27. The stove of any of claims 20 to 26, which comprises a flue, arranged to convey the combustion gasses from both boiler and cooker burners away from the stove once they have been used to heat the appropriate part of the stove.

28. The stove of claim 27 in which the exhaust fan is provided at, or at least closer to, the distal end of the flue.

29. The stove of claim 27 or claim 28 in which the flue comprises, in the preferred embodiment, a pipe of diameter less than 60mm.

30. The stove of any of claims 27 to 29 in which the control unit is arranged to control the speed of the exhaust fan dependent upon the movement of air around the exhaust fan outside the flue.

31. The stove of any of claims 20 to 30 in which the control unit is arranged to fire either of the burners in a modulated manner, depending upon the desired heat output.

32. The stove of claim 31, which is arranged such that the burner output is modulated in use by varying the amount of fuel provided to the burner for combustion.

33. The stove of claim 32 in which fine control over the level of combustion in use is achieved by modulating the speed of the air intake and/or exhaust fans.

34. A stove comprising a hotplate and an oven, and a cooker burner arranged to burn fuel to produce combustion gasses to heat the hotplate and the oven, the stove defining a cooker gas flow path for combustion gasses from the cooker burner, past the hotplate and the oven to heat the hotplate and the oven and then to an exit, in which the flow path diverges at the hotplate such that, in use, only a part of the combustion gasses from the cooker burner directly pass the hotplate, the remainder passing directly to the oven.

35. The stove of claim 34 in which the flow path recombines after passing the hotplate: this would allow the combustion gasses which have passed over the hotplate to continue to the oven where they may be able to pass further heat to the oven.

36. The stove of claim 34 or claim 35, in which the flow path passes over three sides of the oven, before passing to an exit from a cooker part of the stove.

37. The stove of any of claims 34 to 36 in which the stove comprises a further oven, around only one side of which the flow path passes, the part of the flow path which passes the further oven being the same part as passes the third of the three sides of the oven.

38. The stove of any of claims 34 to 37 in which the flow path comprises a baffle at the point where the flow path diverges.

39. The stove of claim 38 in which the baffle is arranged to direct, in use, combustion gasses in two directions.

40. The stove of claim 39 in which the two directions are towards the hotplate and towards the oven.

41. A stove comprising in combination a cooker and a boiler for hot water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, the stove further comprising a heat exchanger arranged such that combustion gasses from the boiler burner flow, in use, in order to extract heat from the combustion gasses, in which the heat exchanger comprises first and second heat exchanger units, arranged such that combustion gasses from the from the boiler burner pass, in use, through first and second units sequentially, the second unit being a condensing heat exchanger unit, wherein, in use, the combustion gasses passing therethrough are cooled to the point where water vapour in the combustion gasses condenses and wherein the first and second heat exchanger units share a common wall.

42. A stove comprising in combination a cooker and a boiler for heating water, the stove comprising a boiler burner for the boiler, a cooker burner for the cooker, in which the boiler burner and the cooker burner are independently controllable and are both arranged such that, in use, they burn fuel to produce combustion gasses, further comprising a common flue for removal from the stove of the combustion gasses from both boiler and cooker burners, in which the flue comprises a pipe extending from the stove, having a diameter of less than 75mm.

43. The stove of claim 42 in which the diameter is less than 60mm 44. The stove of claim 43 in which the diameter is about 54mm.

45. A stove substantially as described herein with reference to the accompanying drawings.