The invention relates to a hearth comprising a rear wall extending at least on one side to a height above the burner, at least one secondary air feed opening close to a lower end of the rear wall and a combustion gas discharge connecting to an upper end of the rear wall.

Such hearths are generally known and, in addition to a decorative function, have the function of heating the space in which they are disposed.

The invention has for its object to provide a hearth of the above described type which in any case also has this decorative function.

This object is achieved in the hearth according to the invention in that the burner has at least one effectively discrete burner opening and is adjusted such that it can burn with a long yellow flame, wherein the height of the rear wall is greater than the length of the flame and the rear wall extends at a distance supporting the flame relative to a vertical through the burner opening. A very attractive decorative effect is achieved due to the flickering of such a long yellow flame.

Because the rear wall extends at a suitable distance relative to a vertical through the burner opening, it provides for stabilization of the long yellow flame which is in principle not very stable. The appropriate distance of the rear wall relative to the vertical through the burner opening, i.e. from the flame, can be determined experimentally in simple manner by a skilled person. Too small a distance will result in the flame making contact with

the rear wall, which can lead to soot formation. Too great a distance results in instability of the flame.

An "effectively discrete burner opening" is understood to mean a combustion gas outlet of the burner such that the flame is formed therethrough with a considerably smaller initial diameter than the length or height of the flame. The burner opening can in reality therefore consist of a number of small openings lying close together.

The rear wall ensures a stable upward airflow in the region of the flame, whereby the flame remains stable.

According to a further development, a glass front wall is situated opposite the rear wall. The flame region is hereby wholly enclosed, thereby to very large extent avoiding a disruption of the upward airflow, and therefore disruption of the stability of the flame.

The rear wall is preferably curved in a semicircle. Additionally or alternatively, the glass front wall can also take such a form and, instead of the semicircular form, a curvature can be realized or a form with vertical facets, each in the form of a plate, or any other form with which the length of the flame (the height thereof) can be extended in co-action with the airflow. These forms are very suitable for the purpose of obtaining the desired stability at a desired flame length, and moreover provide an attractive appearance. A very suitable further development is characterized in claim 4. The rear wall hereby heats up quickly and acquires a relatively high temperature, which greatly enhances the generating and maintaining of the stable upward airflow, and therefore the maintaining of the long yellow flame. According to a preferred embodiment, the rear wall is of enamelled steel plate.

Another possibility for properly stabilizing the flame is 'characterized in claim 6. A high temperature of the rear wall

can hereby also be achieved, resulting in the desired effect of stabilizing the long (high) yellow flame.

A suitable embodiment is characterized in claim 7 by applying ceramic material. The invention will be further elucidated in the following description with reference to the accompanying figures showing a preferred embodiment of the invention.

Figure 1 shows a perspective view of a built-in hearth according to the invention.

Figure 2 shows a horizontal cross-section of the hearth of figure 1 along line II-II in figure 1.

Hearth 1 comprises a burner 5 which in this case has one effectively discrete burner opening 6. Gas and primary air feed means, not further shown here, are adjusted such that in the active situation burner 5 generates a long yellow flame 11. It will be per se apparent to a skilled person how such a burner must be adjusted in order to obtain a long yellow flame. The primary air feed in particular will be very limited or absent.

As shown particularly in fig. 2, the hearth is provided with a rear wall 8 behind burner 5 and in particular behind flame 11, which rear wall 8 has a greater height than the length of the flame. Rear wall 8 extends at a suitable distance from a vertical line through burner opening 6 such that this rear wall 8 supports flame 11.

"Support" is understood in this case to mean that the real wall causes an upward airflow in the region of flame 11 such that flame 11 can burn in stable manner. The distance from rear wall 8 to flame 11, and so to the vertical axis through burner opening 6, is such that this distance is not too small, whereby soot formation could occur on rear wall 8.

For a good supporting action, i.e. for a stabilizing action, the distance is however also not (much) greater than is necessary to avoid this soot formation.

Since the gas supplied via burner 5 combusts substantially with secondary air, a secondary air feed opening 7 is formed at the lower end of rear wall 8. The secondary air flows upward along the rear wall as a result of heating of the air at the position of flame 11.

For a further stabilization of the flame, and also for safety reasons, hearth 1 is provided with a glass front wall 9. The pane 9 ensures that the airflow inside the hearth, i.e. at the position where flame 11 burns, is not disrupted by for instance draught.

A further improvement in the stability of flame 11 occurs when rear wall 8 is heated. The air from the secondary air feed opening 7 hereby flows evenly upward along wall 8.

Rear wall 8 is heated rapidly when it is externally heat- insulated. The heat radiating onto the wall from flame 11 is then not discharged but results in heating of this rear wall 8, and so to an improvement in the stability of the airflow and therefore of flame 11.

Wall 8 is then suitably manufactured from enamelled steel plate. A suitable embodiment can be realized in simple manner by making use of steel plate. Another option for rapid heating of rear wall 8 is to embody this in a material with a high resistance to heat conduction. Suitable material for this purpose is ceramic material .

As shown in the figures, hearth 1 is accommodated with its frame 3 in an opening 4 of a wall 2. A border 10 is arranged around pane 9 for a tidy decorative finish. This border has an outer surface which is an extension of rear wall 8. An optically attractive entity is thus obtained

wherein it appears as if rear wall 8 and border 10 are formed integrally.

It is noted that the invention is not limited to the embodiment shown in the figures. This embodiment is shown only to give a possible embodiment of the invention.