Heating appliances of the kind specified conventionally fall into two groups, a first being a gas appliance, connected to a source of gas, such as propane or natural gas, in which the products of combustion are vented directly into the living area, conventionally through a catalytic converter to reduce the products of incomplete combustion delivered to the area.

The second type of gas appliance is one having an exhaust outlet which in use is connected to a flue, whereby the products of combustion are vented to the exterior atmosphere. Conventionally such appliances are provided with flow passages to extract residual heat from the exhaust gases. However, the efficiency of such flow passages is compromised by the need to ensure good "drawing"of the products of combustion into the flue.

Additionally, with gas appliances of the second type, leakage of the products of combustion can often occur into the living area, such leakage is a significant risk to health and results in many deaths and casualties every year.

Thus it is known in gas fires of the second type, to incorporate a catalytic converter located adjacent to the exhaust outlet, through which products of combustion may flow from the combustion chamber to the flue.

One advantage of such fires is that flow of a small quantity of combusted gases, on exiting the catalytic converter, into the room being heated, is acceptable, although the majority of the combusted gases will be withdrawn through the flue.

Difficulty however is encountered, that under certain weather conditions, down draughts may be produced, which will with existing heaters cause reverse flow of gas through the catalytic converter, and to cause products of combustion to flow into the room being heated without the gases having been subjected to the secondary catalytic oxidation.

This is of course very undesirable, and negates the safety advantages of using a catalytic converter.

Indeed, suggestions have been made to overcome this problem, which involve the use of oxygen depletion gauges, or carbon monoxide sensors, in the room being heated.

Conversely, the problem is solved in accordance with this invention by the provision of baffle means to prevent down draught from flowing through the catalytic converter, and preferably which is operative to direct down draught directly into the room being heated.

By this invention, a number of benefits may be obtained, as follows: a) the baffle ensures that in the event of a draught down the flue, the products of combustion will continue to be drawn through the catalytic converter ensuring continued safety of operation. b) the products of combustion which are vented to the external atmosphere have reduced gases of incomplete combustion, such as carbon monoxide, and are thus less damaging to the external environment ; c) should the products of combustion enter the living area, for example by a flue blockage or down draught, the levels of the dangerous gases resulting from incomplete combustion will be greatly reduced as they have already passed through the catalytic converter; d) the catalytic converter, by oxidising airborne pollutants or gases which would otherwise be combusted incompletely, extracts further heat from the combustion process ; e) the baffle preferably defines a labyrinth flow passage which may be utilised to extract heat from the exhaust gases.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a gas appliance which has been selected for the purposes of illustrating this invention by way of example.

In the accompanying drawings: FIGURE 1 is a schematic sectional view of the gas appliance which is the preferred embodiment of the invention, shown operating in normal use; and FIGURE 2 is a view of the gas appliance shown in Figure 1, illustrating the direction of gas flow in the event of a down draught.

The invention is shown in Figure 1 coupled to an existing chimney opening, but could be coupled directly to a flue or the like.

The gas appliance which is the preferred embodiment of the invention is particularly of the kind specified, being for use in the heating of a domestic living environment, and is specifically for use with a flue 26, comprising a housing 6 defining a combustion chamber 8, within which a gas burner 12 is located. Gas from a supply (not shown) is fed to the burner 12, and is burned thereby, in the presence of air.

The combustion chamber may be defined in part by a rear wall 14, which defines an auxiliary flow path 16, to pass air around the appliance and therefore extract more heat for the living area.

Located in the gas appliance is an exhaust outlet 18, within which outlet a catalytic converter 20 is located. Extending adjacent to the exhaust outlet 18 is a labyrinth passage, comprising a baffle plate 22, and a top plate 24, across which the products of combustion flow as shown by the arrows, towards the flue 26.

In the event of a down draught, air flowing down the chimney or flue will be directed primarily forwardly by the baffle means into the room being served, allowing the products of combustion to continue to flow through the catalytic converter, and to be ducted into the room being served, ensuring that no un-catalysed gases flow into the room being served.

By the use of the catalytic converter 20, a higher degree of safety and efficiency may be ensured, the flow of gases up the flue may be slowed allowing more heat to be extracted by the appliance, in the event that some down draught or flue blockage is encountered, causing the products of combustion to enter the living area, since the products of combustion have been passed through the catalytic converter, the appliance will continue to operate safely.

Whilst the invention has been described herein in relation to a gas fire, it will be appreciated that it may be utilised in other appliances, such as gas boilers, walls heaters etc.

In the present specification"comprises"means"includes or consists of' and"comprising"means"including or consisting of'.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.