GB2530061A

GB2530061A - A gas fire

Info

Publication number: GB2530061A
Application number: GB1416068.3A
Authority: GB
Inventors: Robert A Charmer
Original assignee: NU FLAME Ltd
Current assignee: NU FLAME Ltd
Priority date: 2014-09-11
Filing date: 2014-09-11
Publication date: 2016-03-16
Also published as: GB201416068D0

Abstract

The invention relates to a gas fire comprising a burner and including a heating zone, the burner is adapted to draw combustion air from an aeration box with and inlet in fluid communicating with a heating conduit which extends from the box inlet through the heating zone to a conduit inlet. The fire is arranged such that, in use, a flammable gas burned in the burner heats the heating zone and air from adjacent the fire, at substantially ambient temperature, is drawn into the heating conduit, is heated as it passes through the heating zone and flows to the aeration box for use as combustion air in the burner. Preferably the inlet is arranged below the burner and arranged at or adjacent to the front face of the housing.

Description

A Gas Fire The invention relates to a gas fire, particularly to an open fronted gas fire with a convection channel and also particularly to gas fires for domestic use. The invention extends to a method of operating such a fire.

Domestic gas fires have been available for a number of years, and are now available in a wide variety of different styles and configurations. They were originally introduced to replace solid fuel fires, such as wood and coa( fires, and take advantage of low Natural Gas fuel costs.

However, over time as designs have been provided to better replicate the realism of a solid fuel fire they have achieved this at the expense of the efficiency. This was not seen as a significant problem when gas prices were low, but the continuing increase in fuel costs, along with increasing awareness of environmental concerns, has led to an increased demand for more efficient gas fires.

One way in which the efficiency of gas fires can be improved is by reducing the amount of warm air from the room that s drawn into the fire. This is most commonly achieved by including a glass panel across the front of the fire in front of the fuel bed One major drawback of this approach is that the aesthetics of the fire are compromised, so that the fire lacks the authentic look and feel associated with an open-fronted design. The desire to have a gas fire which is visually similar to a traditional open-fronted solid fuel fire is one main reason why open-fronted gas fires remain popurar despite their relative inefficiency. The amount of radiated heat from an open-fronted fire is also slightly higher since glass is a thermal insulator and in itself reduces the radiant heat that is produced by the glowing fuel bed A number of other more efficient heating solutions are available, but most if not all suffer from the above mentioned problem that they lack the aesthetic appeal of a real', solid fuel, fire. Open-fronted gas fires remain the only practical way of achieving a similar aesthetic appeal, so it has been necessary for people to make a choice or compromise between aesthetics and efficiency when choosing a fire.

It would therefore be beneficial if a fire were available which combined the aesthetic benefits and greater radiated heat of an open-fronted design with the operating efficiency typicaJy associated with glass-fronted fires.

It is an object of the present invention to provide a gas fire that addresses some of the issues outlined above.

According to the invention there is provided a gas fire, the gas fire comprising a burner and the fire including a heating zone, the burner adapted to draw combustion air from an aeration box, the aeration box having a box inlet communicating with a heating conduit, the heating conduit extending from the box inlet through the heating zone to a conduit inlet and the fire arranged such that, in use, a flammable gas burned in the burner heats the heating zone and air from adjacent the fire, at substantially ambient temperature, is drawn into the heating conduit, is heated as it passes through the heating zone and flows to the aeration box for use as combustion aftin the burner.

By pre-heating the combustion air used by the burner in this way a more efficient fire can be constructed since the combustion air does not need to be warmed by the burner flames and consequently the fuel bed heats up more quickly. The combustion air drawn to the burner from the aeration box by the action of the burner is called Primary Combustion Air, with Secondary Combustion Air being the air within which the fuel combusts, for example air that is drawn to the frames across the fire. Primary Combustion Air in this case is drawn to the burner through entrainment of air from the aeration box by the burner or an injector. The fire according to the invention has been designed to increase the efficiency of the fire within the confines and requirements of BS79771:2013. This standard allows the quoted efficiency to be used in the UK Governments Standard Assessment Procedure (SAP) for Energy Rating of Dwellings.

It should be understood that the term gas fire is intended to cover fires in which a flammable gas is a source of fuel, including decorative fires, domestic fires for heating some or all of a domestic environment, commercia] fires for heating some or all of a commercial environment and also includes stoves in which the heating is primarily intended to heat a stove enclosure for cooking.

The flammable gas could be, for example propane, butane, a bio-gas, Natural Gas, or a mixture of these or other gasses The flammable gas may be the primary fuel source and is preferably the only fuel source burned in the fire. The gas fuel is preferably a natural gas which is supplied to the burner. The gas may be supplied to the burner through a distribution network or from a pressurised bottle or canister.

A gas fire may include a matrix for supporting a fuel bed, which may comprise, for example artificial coals, or other materials, which can be used to simulate a real', solid fuel, fire, or for decorative purposes. The fuel bed heats up when the fire is in use and can be used to radiate heat into a room, or other space adjacent the fire. The fuel bed is heated in use and will typically glow. A matrix can allow an increased volume of fuel bed to be used which enhances the thermal storage ability of the fire.

The fire may include a housing. The housing may be entirely enclosed around the fire and include a base, opposed skie walls, a rear wall, a roof through which a flue passes and a front wall. At least part of the front wall may be made of glass. The housing may include an open front portion in the case of an open fronted gas fire. In a decorative fire the housing may be rather minimal extending mainly below the burner and up a rear of the fire to a level that is preferabFy lower than that of a fuel bed included in the fire so that the housing above the level of the burner is substantially hidden. The housing may include legs to raise the fire from the floor, for example to provide space for controls, and may include one or more openings through one or more walls. For example the fire may be an open fronted fire, or may include air inlets and/or outlets, or access apertures to allow access to controls or other components. The access apertures may be concealed by one or more access panels. The housing may include insulated portions and I or heat stores which are heated by the action of the fire during use and then radiate heat. The housing may also include a control section in which there are located controls, for example manual controls, for the fire.

The burner may be any suitable burner for burning gas. It is preferred that the burner used in the present invention is adapted to enhance the draw of combustion air from the aeration box by creating a region of reduced pressure into which air from the aeration box will flow.

The burner adaptation may include the use of one or more verituris, preferably a short venturi with a shallow diffusing baffle with gauze strips to prevent light back of the gas into the burner as is known in the art. It is preferred that air is drawn into the heating conduit by a reduction in pressure created by the gas flow through the burner. Preferably air is drawn into the heating conduit only by a reduction in pressure created by the gas flow through the burner. This reduces the reliance of the fire on external power sources such as electricity to drive a fan. It should be noted that a fan could be used to move air towards the fire from a distant location.

It should be noted that a venturi can draw too much air to the burner from the aeration box and too much air can result in very blue flames with tight flame cones which may buzz and be noisy. It is known to restrict venturi inlet to control the f(ow to an appropriate level.

It will be understood that each fire, burner and fuel bed design will vary the amount of primary, or combustion, air used and so will require appropriate sizing of sizes of ducts, aeration boxes and conduits to ensure that there is no unintended restriction.

The heating zone of the heating conduit may include a separate heat source, but preferably is heated in use, at least in part, and preferably substantJally entirely, by the heat generated by the burner. This provides an efficient arrangement in which the gas fuel heats the room and also pre-heats the combustion air and reduces the reliance of the fire on another energy source, for example electricity. The heating conduit may comprise more than one heating zone, for example if the heating conduit makes several passes through a region of increased temperature The heating zone may be the hottest, or one of the hottest, pads of the heating conduit. It is preferred that the heating zone is arranged at or adjacent the flue outlet as the flue outlet is typically one of the hottest parts of a lire. The heating conduit courd extend into the flue outlet and the heating zone may include the flue outlet. The heating zone may be a region of the fire within which the air passing through the heating conduit is heated, preferably to a temperature above about 60°C, above about 100°C, above about 120°C and most preferably above about 150°C. By extracting heat generated by the burner and using it to heat the combustion air it is possible to make use of heat that might otherwise be exhausted up a chimney, or be otherwise lost.

The aeration box is arranged such that the burner draws primary combustion air therefrom.

The aeration box may be any suitable size and shape and essentially forms a plenum chamber from which the burner can draw combustion air. The aeration box is preferably of a size sufficient that is does not substantially restrict the availability of air for the burner.

It is preferred that substantially all the primary combustion air for the burner is drawn from the aeration box as this means that substantially all the primary combustion air (air that is used in the combustion of the flammable gas) used in the burner is pre-heated and this is likely to provide a higher efficiency than allowing a secondary source of non-preheated air to provide combustion air to the burner. It should be understood that the aeration box may not be a single box, but could comprise multiple chambers, particularly for a large burner. For fires with more than one burner a single aeration box may be used to supply both burners, or one or more burners may have their own aeration box.

It is preferred that the aeration box is substantially sealed around substantially the entire area from which the burner draws primary combustion air as this will help to prevent unwanted, non-preheated, air from reaching the burner. It should be understood that secondary combustion air may be drawn into the burner from above the burner, but is preferred that all primary combustion air passing to the burner comes from the aeration box.

The box inlet from the heating conduit Fs the inlet through which it is preferred that substantially all the air entering the aeration box passes. The box inlet may be only a single inlet, or may comprise a plurality of inlets from one or more heating conduits.

The heating conduit may take many forms. For example, it could comprise a box section channel, a circular section tube channel and may include one or more plenum chambers. A plenum chamber is used herein to refer to a chamber having a larger cross sectional area than the conduit or channel that draws gas from the chamber. Such a chamber helps to smooth irregularities in the flow through a system by providing a volume in which at least some mixing of incoming gas with the chamber content occurs before the incoming gas is drawn to an outlet; In this way things like sharp temperature variations may be reduced. At least a part of the heating conduit may be used for guiding, not only air that will become combustion air, but air which is intended for other purposes, for example convection air. The heating conduit may be arranged such that the conduit is defined, at least in part by a wall of a housing or of a firebox within the housing. For example, the conduit may include a box section duct with one wall of the duct provided by a wall of the housing or firebox. In such an embodiment the heating conduit is located on, or at least adjacent to, the wall or firebox, although it shourd be noted that such a construction is not required for this to be the case.

The conduit inlet is arranged and configured to draw air at a substantially ambient temperature from adjacent the fire into the conduit. The air at a substantially ambient temperature might be indoor or outdoor air and there may be an ambient air conduit delivering air to the conduit inlet of the fire. The term ambient' is used here to refer to air that has not been substantially heated by the operation of the fire above the temperature of the atmosphere from which it is drawn. Obviously air drawn from a room being warmed by the fire has been heated by said fire, but would stil! be considered to be at an ambient temperature (typically below about 30°C for use in 887977, but also includes temperatures below about 30°C because at his temperature a room may be considered too hot to require heating by a fire). The conduit inlet may be an opening in a housing or an opening at the end or a conduit into whFch air can flow. The conduit inlet may be open, or may be directly coupled to an ambient air conduit. An ambient air conduit guides air to a location adjacent the fire without any significant heating or cooling and may comprise, for example, a pipe or duct. Such an ambient air conduit may feed directly into the conduit inlet of the fire, or may feed ambient air to an area adjacent saFd conduit inlet so that the ambient air can be drawn into the conduit inlet.

The conduit inlet is preferably arranged to reduce the possibility that combusilon products from the burner might leak into, or otherwise enter, the conduit. It is preferred that the conduit inlet is arranged below the burner. It should be noted that relative terms such as above and below are used to refer to an in-use' orientation. By arranging the conduit inlet below the burner the risk of combustion products, which are typicalLy hot and therefore less dense than the surrounding air, entering the conduit is reduced which increases the safety of the fire.

The heating conduit may extend from a region below the burner to a heating zone above the burner and back to the aeration box below the burner. The heating conduit may comprise a substantially U' shaped duct on a rear face of a housing. The duct may have any suitable cross section shape1 for example substantially rectangular, substantially circular or substantially semi-circular and acts as a conduit for air. It is preferred that such a duct has a substantially rectangular cross section for ease of fabrication. The U' shaped duct may include first and second outer walls, but only one dividing wall arranged between a duct portion leading away from the burner and a duct portion leading towards the burner. Such an arrangement, again, facilitates construction. It should be understood that any means to separate the gas flows with in the two pads of the U' shaped duct could be used. There may be a series of such ducts through which air must pass to reach the aeration box. A U' shaped duct may feed into further channels, ducts or conduits that form part of the heating conduit.

The heating conduit may be substantially sealed such that substantially no products from combustion at the burner can enter the heating conduit along its path. SubstantEally sealing the heating conduit and aeration box also allows tuning of the primary air system. The location of the heating zone within the fire, or the residence time of aLr within said heating zone, could be adjusted, for example by adjusting the path of the heating conduit or the cross sectional area of the conduit, to allow for a tuning of the pre-heating of the combustion air The conduit inlet may be arranged in, or adjacent, a front face of a housing, the front face of the housing intended to be visible when the fire is in use. For example a decorative fender or fascia may be employed to provide the visible front face of the fire and in such a case the conduit inlet may be concealed behind such a fender or fascia, but is still located at or adjacent the front face of the fire. Domestic fires are often situated in apertures Formed at the base of a chimney of a predetermined size. It is usual that a fire is selected to fill the aperture and this could lead to blocking or restricting of the conduit inlet if that inlet was sited in a side, base, top or rear wall of a housing. The front lace, which is intended to face into the room and be visible during use, is typically unobstructed: The gas fire is preferably be an open fronted fire1 but may be a glass fronted or decorative lire.

The air in the heating conduit passing through the heating zone may be heated to at least 60°C, at least 100°C, preferably at least 120°C and more preferably at Feast 150°C. This represents a tempeiature increase of at least 30°C over what would be typical for ambient temperature, which istypically considered to be no more than 3000. It is preferred that the air drawn into the conduit in!et is at a temperature of no more than 30°C.

The heating zone of the fire is preferably arranged at or adjacent one of the hottest parts of the fire, for example it may be arranged at or adjacent a flue outlet from the fire. This is typically one of the hottest parts of the fire and is therefore a good place from which to transfer heat to the air in the heating conduit. A flue outlet might be located in a roof of a housing and the heating zone may be located adjacent that outlet so that air within the heating zone is heated, at least in part by heat from the flue outlet. The heating zone may be located just below the flue outlet, or may extend around it. The heating conduit may be located, for example on or adjacent a rear wall of the fire. The heating zone is preferably arranged at or adjacent on of the hottest parts of the fire that is at or adjacent a housing as this avoids having to construct conduits or pipes that run, unsupported, into space within which the fuel bed and flames are located, although such unsupported pipe runs are possible if a particularly desirable heating zone is identified. The heating zone is defined by the arrangement of the heating conduit and is the hottest part of that conduit. It may be possible to alter the arrangement of the heating conduit so that the heating zone can be moved to alter the amount of pre-heating provided. The heating zone may be arranged within the fuel bed wfth the heating conduit passing through the fuel bed.

The heating conduit may include a plenum chamber which is heated by the heating zone from which air is drawn to the aeration box. Such a heated plenum could be formed between a double skin, for example on the rear of the fire. Such a double skin may be formed by including a firebox within a housing such that a rear wall of the firebox forms a front skin and a rear wall of the housing forms a rear skin. The air between the two skins is heated by the fire and provides a heated plenum from which air is drawn to the aeration box.

A housing may include a convection channel, the convection channel extending from an inlet below the burner up a rear face of the housing to an outlet. The convection channel may extend along a roof of the housing to the outlet, which may be located at, or adjacent, a front face of the fire. Such a convention channel can be formed in the same way as the plenum mentioned above, by providing a double skin for the fire. Using a convection channel allows air to enter below the burner, pass up between the double skin and be heated by the fire and then exit via an outlet so that the heated air enters a space being heated by the fire. Such a convection channel increases the efficiency of a fire by harvesting some of the heat that would simply heat the rear of the fire and structure behind it and redirecting that heat into the space to be heated, Air below the burner may provide a plenum chamber within the convection channel and I or the heating conduit. The inclusion of such a plenum chamber below the burner facilitates construction and help to avoid any contamination of the air within the heating conduit or convention channel by combustion products from the burner.

At least part of the heating conduit may be located within the convection channel and I or the heating conduit may include at least part of the convention channe! and a heating duct, the convection channel providing a plenum chamber from which the heating duct draws air to the aeration box. Making use of the convection channel to also provide at least some of the heating conduit reduces the complexity of the fire as one structure is able to perform two functions. Drawing air from within the convection channel aso helps to reduce the amount of dust or other particulate contaminants into the aeration box which can reduce the frequency of servicing that the tire might be required to maintain the efficiency of the fire.

The heating conduit may include insulated portions in regions where it is desired to avoid a loss of heat from the conduit to the surrounding atmosphere.

A housing may include a separate firebox within which the burner and fuel bed are located.

The firebox is typically visible in use as the rear face of the fire. In some cases the housing forms the firebox.

At least part of the heating conduit may extend into the firebox. The heating conduit may be arranged on one or more walls of the ftrebox, or at least some of the heating conduit may extend, substantially unsupported, across part of the firebox.

It is preferred that there is only a single heating conduit that feeds into the aeration box as this facilitates manufacturing and servicing of the fire.

In order for the air in the heating conduit, or the convention channel, to be heated by the burner there must be heat transfer from the combustFon products of the burner to a part of the heating conduit of convection channel and from the heated part of the heating conduit or convection channel to the air flowing therein. Such heat transfer could be facilitated or enhanced by increasing the surface area of heating conduit or convection channel on one or both surfaces (interior and exterior) across which heat is to be transferred. A suitable heat exchanger, for example a gas-gas heat exchanger, may be used for this purpose with one side being air to be heated and the other side being the combustion products. The heat exchanger may be a simple box or chamber through which the combustion products pass and over which the air flows so that heat is transferred to the air.

The fire may also include a temperature sensor, for example a thermocouple, to sense the temperature of air within the conduit. The temperature sensor may be used to monitor the temperature in the heating conduit and as part of a control system forthe fire. For example the flow of flammable gas into the fire may be controlled based on the temperature of the air in the heating conduit and a desired heat output indicated by a user. Altering the flammable gas flow to the burner based on the temperature of the air in the heating duct may help to control yellowing of the flames and for may help in reducing flammable gas usage relative to a pre-establisbed burn down effect of the fire when preheated primary air is used.

It has also been found that, in tests, burn down of the lire was increased over what would be expected in a (ire without such pie-heating of the primary air. An increase in burn down (a reduction in the amount of flammable gas used at a given feed pressure) enhances the efficiency of the fire for the consumer without any direct intervention. Since there is a feedback mechanism in that the heat of the fire is pre-heating the combustion air fires of this invention tend to reach thermal equilibrium more slowly than conventiona' fires. In tests it was found that thermal equilibrium was reached after 1.5 to 2 hours rather than the 1 hour more normally observed.

The invention also provides a method of operating a gas fire, the gas tire comprising the gas fire comprising a burner and the fire including a heating zone above the burner, an aeration box having a box inlet communicating with a heating conduit, the heating conduit extending from the box inlet through the heating zone to a conduit inlet and the method comprising the steps of: a) using the burner to burn a supply of flammable gas fed thereto to heat the heating zone b) drawing air from adjacent the fire, at substantia!Iy ambient temperature, into the heating conduit; c) heating the air in the heating conduit as it flows through the heating zone to the aeration box; and d) causing the burner to draw combustion air from the aeration box.

This method may be carried out in any of the fires described above.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a schematic cross section through a first gas fire; Figures 2a and 2b show a schematic cross section through second and fourth gas fires; Figure 3 shows a view of the duct of the second gas fire; and Figure 4 shows a schematic cross section through a third gas fire.

Figure 1 shows a schematic cross section through a first fire 1. The fire I is a gas fire which comprises a housing 2 and a burner 4 located within the housing 2. The burner 4 is arranged and adapted to draw combustion air from an aeration box 6 which is attached to the burner support 8, which supports the burner 4 and the aeration box 6. A flammable gas is fed to the burner via an injector 10 which is sealed to the aeration box 6. The fire is controlled by a controller 9, which can be adjusted bya user.

A base 12 of the housing 2 is spaced apart from the aeration box 6 below the burner support 8. The 2 housing also includes a rear wall 14 and a roof 16. The roof 16 includes a horizontal portion 18 and an angled portion 20. An outlet flue 22 passes through the angled portion 20 of the roof 16 to carry the products of combustion to a chimney or other outlet (not shown). Within the fire 1 there is a matrix 24 which helps to support a plurality of synthetEc coals 26 which form a fuel bed 28 which, in use, will be heated by flames from the burner 2 and wih radiate heat into the space adjacent the fire. The matrix 24 also helps to distribute flame from the burner 4 within the fuel bed 28.

A firebox 30 is arranged within the housing to contain the fuel bed 28 and associated combustion products. A liner 32 may be included to protect the firebox 30.

The fire 1 includes a convection channel 34 which extends from an inlet 36, between the firebox 30 and the rear wall 14 of the housing 2, around the flue outlet 22 and across the roof 16 to an outFet 38.

The fire also includes a heating duct 40 arranged within the convection channel 34. The heating duct 40 extends from a heating zone 42 to the box inlet 44 of the aeration box 6 In use, a flammable gas is fed to the burner 4 through the injector 10 and is burned.

Combustion air1 specifically primary combustion air, is drawn from the aeration box 6 to the burner by the action of a venturi (not shown) within the burner 4. The aeration box 6 is substantially sealed to the burner support 8 so primary combustion air for the burner can only be drawn from the aeration box 6.

As air is drawn from the aeration box 6 by the burner 4, air flows into the aeratEon box 6 through the box inlet 44. The box inlet 44 is connected to a heating conduit 46 which extends to a conduit inlet 48. The conduit inlet 48, in this case the same as the inlet 36 to the convection channel 34, draws air at an ambient temperature (not more than 30°C) from a space 50 adjacent the housing 2.

The flow of air is indicated by arrows in Figure 1. Ambient air flows 54 from the space 50 into a lower channel 52 the housing 2 through the inlet 36 and conduit inlet 48. The air then flow 56 up the rear wafl 14 of the housing 2 to then heating zone 42 just below the flue outlet 22 where the temperature of the firebox 30 is typically hottest (or nearly at its hottest).

The air flow is then divided, with some continuing 58, 60 around the flue outlet 22 and across 62 the roof 18 to an outlet 38. This completes the convection channel 34 and passes warmed air back into the space 50. Other air is drawn 64 from the heating zone 42 into the heating duct 40 which runs along the rear of the firebox 30 to the box inlet 44 into the aeration box 6 so that air flows 66 into the aeration box 6 from which the burner 8 can draw primary combustion air. The temperature of the air within the aeration box 6 can be between about 160 and 190°C using such a system.

The fire 1 has an open front 68 to better replicate a solid fuel, real' fire and the various inlets/outlets 3638,48 could be covered or hidden from view of the space 50 by decorative.

or functional, panels (not shown).

In this way a flammable gas burned at the burner 8 heats the heating zone 42 and air from adjacent the housing 2, at substantially ambient temperature, is drawn into the heating conduit 46, is heated as it passes through the heating zone 42 and flows to the aeration box 6 for use as combustion air in the burner 8.

In this embodiment the fire 1 includes a convection channel 34 and the heating conduit 46 comprises a part of the convection channel 34. The convection channel 34 in this case acts as a plenum chamber from which the heating duct 40 can draw heated air from the heating zone 42 to the aeration box 6. The convection channel 34 extends across substantially the entire width of the rear wall 14 of the housing 2, but the heating duct 40 does not. The heating duct 40 may extend less than 50% of the width of the convection channel 34 and may extend across less than 25% of the width of the convection channel 34. The heating duct 40 is substantially centrally located across the width of the fire 1.

Fiàurc 2a shows a schematic cross section through a second gas fire 101. Features that serve the same function in essentially the same way as in Figure 1 will be given the same reference numeral incremented by 100.

The fire 101 includes a housing 102 having a flue outlet 122 in a roof 116 and a burner support 108 which carries a burner 104 and an aeration box 106. Gas is supplied to the burner 104 through an injector 110. A fuel bed 128 sits over the burner 104.

The fire 101 does not include a convecUon path, but a heating conduit 146 is provided, at least in part by a U' shaped duct 70, best shown in Figure 3.

Figure 2b shows a schematic cross section through a fourth gas fire 301. The fourth gas fire 301 is essentially the same as the gas fire 101, but the U' shaped duct 370. that forms part of the heating conduit 346 extends further up the housing towards the flue outlet 322 so that the heating zone 342 is arranged at or adjacent the flue outlet 322. This means that the air in the heating zone 342 is likely to reach a higher temperature than that in the heating zone 142 of the second gas tire 101. It should be noted that the U' shaped duct of the fire 301 is not hidden by the fuel bed 128.

Figure 3 shows a schematic view of a U' shaped duct 70 used in the fire 101 of Figure 2.

The duct is called U' shaped due to the path taken by air that flows through it. The U' shaped duct 70 has an inlet 72, an upward leg 74 and a downward leg 76. The upward and downward legs 74,76 are separated by a divider plate 78. Air passed into the U' shaped duct 70 through the inlet, passes up the upward leg 74, through an aperture 80 in the divider plate 78 and down the downward leg 76 to an outlet 82 which, in use, feeds into the aeration box 106 of the fire 101.

Referring back to Figure 2a, the aperture 80 in the divider p'ate 78 is Located in the heating zone of the fire 101 and is the hottest part of the fire 101 which is substantially concealed by the fuel bed 128. Since the fire 101 does not include convection channel at the rear the U' shaped duct 70 is located on the inside (fuel bed side) of the housing 102 and so it is preferred to conceal the duct 70 behind the fuel bed 128. In use the U' shaped duct draws ambient air from a channel 84 that extends below the burner 104 to a conduit inlet 148 in the front of the fire 101. This allows ambient air from the space 50 in front of the fire to be drawn 154 into the heating conduit 146 through the conduit inlet 148 below the burner 104, through 86 the U' shaped duct 70 and into the aeration box 106 for use as combustion air for the burner 104.

It should be noted that although Figure 2a shows a housing including a roof and flue outlet, the fire 101 may not include such features, for example a fi!e 101 may not include a hosing that extends above the'U' shaped duct 70 and could be placed in conventional fireplace in which the fireplace provides a roof and chimney outlet through which the combustion products can pass. In such an embodiment the housing may be rather minimal with the fire comprising a burner tray supported by legs which sit under an open chimney with a fuel bed supported on the burner. Such a fire would still benefit from the improved efficiency provided by the heating of the combustion air. For example, the housing 102 of figure 2a may stop at the top of the U' shaped duct 70 and the flue outlet 122 could be provided by a chimney of a fireplace in which the fire 101 has been placed. As noted above, channel 84 may not be enclosed by the housing 102 in such an embodiment and the U' shaped channel may draw air from a space beneath the burner 104 which is created by supporting the burner on legs.

Figure 4 shows a schematic cross section through a third gas fire 201.. The third gas tire is similar to the first gas fire 1 in Figure 1, but it does not include a matrix 24 or a liner 32. Due to the similarity between the tires 1 and 201 the same reference numerals wilr be used to indicate features which are substantially identical. In this case the convection channel 34 and associated parts are the same, with the exception of the convention channer inlet 236 and outlet 238 which are covered by decorative/diffusive panels 92 and 94 respectively which act to conceal the apertures into, or out of, the housing 202. The convection channel 34 functions in the same way as that shown in Figure 1.

The fire 201 includes an ambient air duct 88 which directs ambient air from a, possibly distant, space 90 to the conduEt inlet 248, which En this case is located above the burner 4.

This allows ambient air to be drawn from an area adjacent the housing into the conduit inlet 248. In this case the ambient air originates in space 90 and is drawn through the ambient air duct 88.

The conduit inlet 248 is coupled to a heating duct 240 in a heating zone 242. The heating duct 240 is substantiaUy the same as the heating duct 40 shown in Figure 1, except that it extends through the heating zone 242 to the conduit inlet 248 rather than drawing air from the plenum chamber formed by the convection channel 34.

In use air is drawn from the aeration box 6 by the action of the burner 4 and injector 10 and this causes air to be drawn through the box inlet 44 from the heating conduit 246. The heating conduit 246 in this case comprises the heating duct 240 which extends along a rear face of the firebox 30 to the heating zone 242, located just below the flue outlet 22, and then to the conduit inlet 248 in the rear wall 214 of the housing 202 at about the same height as the heating zone 242.

In this case the fire 201 comprises a glass front 96 which substanlially seals a front face of the firebox 30 with the exception of a gap just above the burner support 8.

Since the fire 201 includes a glass front 96 a diverter 100 is included at the flue outlet 22.

The diverter 100 is likely to be a hot pad of the fire 201 and the heating conduit exiends along the burner such that the heating zone 242 is arranged on the diverter 100, above the fuel bed 28 around which the convection channel passes. The heating zone 242 of the heating conduit may include a heat exchanger to enhance the transfer of heat to the air within the heating conduit 246.

It shourd be understood that the above examples have been described by way of example only and features described with reference to one example could be combined with some or all features described with reference to another example. For example a dU shaped duct as shown in Figures 2 and 3 could be used in a fire with a convection channel as shown in Figure 1 and 4. The position of the air inlets and/or outlets could be varied in all examples and a matrix as shown in Figure 1 could be included in other examples. Other combinations will be apparent to those skilled in the art without departing from the scope of the claims.

Claims

Claims 1. A gas fire, the gas fire comprising a burner and the fire incluthng a heating zone, the burner adapted to draw combustion air from an aeration box, the aeration box having a box inlet communicating with a heating conduit, the heating conduit extending from the box inlet through the heating zone to a conduit inret and the fire arranged such that, in use, a flammable gas burned rn the burner heats the heating zone and air from adjacent the fire, at substantially ambient temperature, is drawn into the heating conduit, is heated as it passes through the heating zone and flows to the aeration box for use as combustion air in the* burner.
2. A gas fire as claimed in claim 1, in which the conduit inlet is arranged below the burner.
3. A gas fire as claimed in claim 1 or claim 2, in which the heating zone is above the burner.
4. A gas fire as claimed in any preceding claim, in which the conduit inlet is arranged at, or adjacent, a front face of the housing, the front face of the housing intended to be visible when the fire is in use.
5. A gas fire as claimed in any preceding claim, in which the gas fire is an open fronted fire.
6. A gas fire as claimed in any preceding claim, in which, in use, the air in the heating conduit passing through the heating zone is heated to at least 60°C.
7. A gas fire as claimed in any preceding claim, in which the heating zone of the fire is arranged at or adjacent a flue outlet from the fire.
8. A gas fire as claimed in any preceding claim, in which the heating conduit includes a plenum chamber which is heated by the heating zone from which air is drawn to the aeration box.
9. A gas fire as claFmed in any preceding claim, in which the fire includes a housing which includes a convection channel, the convection channel extending from an inret below the burner up a rear face of the housing to an outlet.
10. A gas fire as claimed in claim 9, in which at least part of the heating conduit is located within the convection channel.
11. A gas fire as claimed in claim 9 or claim 10, in which the heating conduit includes at least part of the convention channel and a heating duct, the convection channel providing a plenum chamber from which the heating duct draws air to the aeration box.
12. A gas fire as claimed in any preceding claim, in which the air is drawn into the heating conduit by a reduction in pressure created by the gas flaw through the burner.
13. A gas fire as claimed in any preceding claim, in which the heating conduit extends from a region below the burner to the heating zone above the burner and back to the aeration box below the burner.
14. A gas fire as claimed in claim 13, in which the heating conduit comprises a substantially U' shaped duct on a rear face of a housing.
15. A gas fire as claimed in claim 14, in which the CU shaped duct includes first and second outer walls, but only one dividing wall arranged between a duct portion leading away from the burner and a duct portion leading towards the burner.
16. A gas fire as claimed in any preceding claim, in which the heating conduit is substantially sealed such that substantially no products from combustion at the burner can enter the heating conduit.
17. A gas fire as claimed in any preceding claim, in which substantially all of the combustion air for the burner is drawn from the aeration box.
18. A method of operating a gas fire, the gas fire comprising a burner and the fire including a heating zone above the burner, an aeration box having a box inlet communicating with a heating conduit, the heating conduit extending from the box inlet through the heating zone to a conduit inlet and the method comprising the steps of: a) using the burner to burn a supply of flammable gas fed thereto to. heat the heatrng zone; b) drawing air from adjacent the housing, at substantially ambient temperature, into the heating conduit; c) heating the air in the heating conduit as ii flows through the heating zone to the aeration box; and d) cau&rig the burner to draw combustion air from the aeration box.
19. A method as claimed in claim 18, in which the gas fire is substantially as claimed in any of claims ito 17.
20. A gas fire substanilally as herein described with reference to, or as shown in, the accompanying drawings.
21. A method substantially as herein described with reference to the accompanying drawings.