Such criteria are now standard in certain environments such as hospitals, nursing homes and creches. While this special safety requirement is generally limited to such buildings there is an increasing interest in such appliances for the workplace, which will also lead to natural specification for home use.

The LST ("Low surface Temperature") specification calls for a maximum touch temperature of 43C. This requirement is conventionally obtained by simply covering a conventional panel radiator with a'purpose made box'with suitable airways whereby it is made impossible for hot surfaces to be touched.

The effect of'boxing'the appliance is to significantly reduce the operational efficiency of the appliance and to create a seldom cleaned'dust trap and health hazard'.

Another significant drawback is the increased size of the unit and resultant loss of available floor and wall space. The user also has either to accept a drop-off in performance or increase the size of the appliance (and box) to make up for losses if the original heat output is to be maintained.

The other alternative to the radiator box is selection of a radiator manufactured to the LST specification. LST performance is usually obtained by incorporating in the design a permanent screen, usually metallic, to encase the heat emitter so as to avoid touching of hot metal parts. Radiators of this type on the market do not generally reach the entire safety standard and again this type of construction means an increase in overall size and loss of operational efficiency.

The present invention seeks to provide a heating appliance which overcomes these problems, and in particular, is so constructed as to reduce the transmission of heat to the outer surface, while maintaining a good level of heating efficiency.

Accordingly, one aspect of the present invention provides a heating appliance comprising a casing with air inlet and outlet apertures, and an air heating passage which connects the inlet and outlet apertures, but is thermally isolated from the outer surface of the casing.

Preferably at least one wall of the heating passage is heated electrically or by fluid e. g. hot water.

Preferably, the air heating passage is constructed from a thermally conducting material, such as metal, which is mechanically connected to the outer casing by a non- thermally conducting material, so as to prevent the conduction of heat from the material of the air passage, to the material of the outer casing, which may also be metal.

Preferably, the mechanical connection between the heating passage and the outer casing comprises a foam filling, such as foamed polyurethane.

In order to improve the heating efficiency while maintaining a compact appliance structure, another aspect of the invention provides a heating appliance having an outer casing with air inlet and outlet apertures which are connected by a"venturi like"air heating passage which is arranged to accelerate the air flow and thereby enhance heat output. Preferably, the air passage also incorporates a plurality of heat transfer fins to improve the transfer of heat to the air passing through the passage.

Depending on the required application, the air passage may be arranged to extend vertically, as in the case of a skirting or panel radiator, or it may be arranged to extend substantially horizontally, in the case of a heating device intended to be installed at the threshold of a door, or incorporated in a window sill. In a preferred embodiment of the invention the appliance is constructed as an assembly comprising a pair of hollow extruded aluminium sections, which are arranged parallel to one another so that their inwardly facing surfaces form a transversely extending air passage between them, and incorporate heating elements to heat the air.

Preferably, the hollow sections are filled with polyurethane so that the outwardly facing surfaces are insulated from the inwardly facing surfaces and the metal structure of the extrusion is cut away to form air breaks which prevent the conduction of heat from the inner surfaces to the outer surfaces.

Some embodiments of the invention will now be described, by way of example with reference to the accompanying drawings, in which: Figures 1 a, 1 b, and 1 c are respectively a side view, a plan view, and a schematic cross-section of a first type of heating appliance according to the invention; Figure 2 is a vertical cross section through a multiple version of the heating appliance of Figure 1; Figures 3a and 3b are vertical cross sections through joints between the sections of Figure 2; Figure 4 is a perspective view of an alternative version of the heating appliance of Figure 1; Figure 5 is a vertical cross section showing in more detail. the internal construction of the device of Figure 1; Figure 6 is a vertical cross section through a second type of heating device according to the invention; Figure 7 is a vertical cross-section through an alternative form of the device of Figure 1; Figure 8a is a vertical cross-section through an alternative form of the device of Figure 6; Figure 8b is a partial view showing internal features of the construction of Figure 8a; Figure 9 is a vertical cross-section through a further alternative form; Figure 10 is a vertical cross-section through a typical suspended floor heater arrangement ; Figure 11 is a cutaway view of an integral sill heater based on the same structure as Figure 10; Figure 12 is a corresponding view of a"sill-line"heater ; Figure 13 is a corresponding view of a dado heater; Figure 14a is a vertical cross-section through dado heater; Figure 14b is a detailed view of part of the heater of Figure 14a; and Figure 14c is a perspective view of the detail of figure 14b.

Referring firstly to Figure 1, Figure 1a is a side elevation of an elongate heating module which is intended to be floor mounted, and comprises a pair of hollow aluminium extrusions, 2 and 4 (Figure 1 c) which are held together by upper and lower grille assemblies 6 and 8 (Figure 1 b) and end caps 10 and 12 which (in the case of an electrically heated version) house electrical connections to the internal heating elements.

The gap between them forms a transversely extending heating passage for the air.

As shown in Figure 2, a number of modules of the type shown in Figure 1 can be stacked so as to form a"panel radiator"which can be wall mounted, and in the example shown, there are five stacked modules 14,16, 18,20 and 22 fixed to a wall mounting bracket 24.

As shown in Figure 3, the heater modules can be interconnected so that the upper and lower edges of their side walls abut directly, as shown in Figure 3a, or they may be connected together by means of an elongated. ventilated spacer 24, as shown in cross- section in Figure 3b. As illustrated, the spacer comprises upper and lower flanges 26, 28 adapted to slide into corresponding slots in the edges of the members 14 and 16, and a central slatted grille which allows air to pass into the interior of the assembly, to be heated by the internal"chimney"and to subsequently exit through the upper grille 6.

Figure 4 is an enlarged perspective view of a heating module similar to that of Figures 1 to 3, but utilising water heating, rather than electric element heating. Again, the outer body comprises a pair of facing extrusions 2 and 4, upper and lower grilles 6 and 8, and end caps 12, but in this case, the end caps include water flow and return connections 30 and 32 or other means for coupling the module to an adjacent module.

Once again, as illustrated by the dashed lines 34, the modules may be stacked vertically to increase heat capacity.

Figure 5 is a more detailed cross sectional view of a construction, which is applicable to both the electric version of Figures 1 to 2, and the water heated version of Figure 4. As shown in the drawing, each of the extruded assemblies 2 and 4 comprises a flat outer wall 36,38, and a curved inner wall 40,42. Thus the cross section of each extrusion is in the general shape of a vertical elongated letter"D", so that in the assembled condition as shown, an air passage 44 is formed between the two curved faces 40 and 42, which has a venturi like cross section which is wider at the top and bottom 46,48 respectively.

As will be seen from the drawing, the upper and lower edges of the extrusions are formed with slotted flanges 50,52, which locate mating flanges on the upper and lower grille assemblies 6 and 8, so as to hold the two sides together. Alternatively, as illustrated in Figures 3a and 3b above, these slotted flanges may be used to interconnect upper and lower assemblies, in a stacked configuration.

The inner walls 40 and 42 of the extrusions are integrally formed with longitudinally extending tubular chambers 54,56, to accommodate an electric heating element, or hot water in the case of a"water based"system. Since these passages are integrally formed with the extrusion, it will be appreciated that heat is conducted directly to the inner surfaces of the extrusions, so that the air flow through the"chimney"44 is directly heated by these surfaces, and in addition, additional metallic fins 58 may be positioned in the passage, so as to increase the surface area in contact with the air.

In order to prevent heat conduction from the curved inner surfaces 40,42 to the outer surfaces 36, 38, the internal spaces 60,62 of the extrusions are filled with insulating foam such as polyurethane, and thermal breaks 64 are formed at the top and bottom of the structure, by providing discontinuities in the material at the junctions of the inner and outer surface members of each extrusion. This may be done by cutting the metal after the foam has cured. Thus it will be appreciated that although each extrusion is formed initially, as a continuous flat"tube", the metallic inner and outer walls of the extrusion are then no longer directly connected to one another, but instead are only connected by the cured body of foam between them. Alternatively, instead of being formed as hollow extrusions, each member can be made in two halves which are held in position while foam is formed between them, or their edges may be connected by a separately formed thermoplastic gasket.

In order to accommodate internal wiring, and also to provide housing space for thermal safety cut-outs, hollow box section members 66 are positioned inside each extrusion, before it is filled with foam. Consequently, if the internal surfaces should become overheated for any reason, for example because the air inlet or outlet are blocked, the increase in temperature will be detected by the thermal cut-out before the outer casings become too hot, and the heat source will then be shut down.

Figure 6 illustrates a heating module which operates on a similar principle, but in which the air passage is arranged so that it normally extends horizontally, rather than vertically. Consequently, the device can be used as a threshold or window sill heater.

As illustrated, the heater again comprises a pair of facing hollow extrusions 70 and 72, which in this case are arranged one above the other with the lower extrusion 70 adapted to form a base for the structure, whilst the top surface 102 of the upper extrusion 72 forms a foot tread or window sill surface. The lower extrusion 70 is integrally formed with tubular heating channels 74,76 which may carry electrical heating elements, or water flow in the case of a water heated system, in which case they will be copper lined. The remainder of the internal volume of the lower extrusion 70 is filled with insulating foam 78, and thermal breaks 80,82 are then formed in the extrusion, so that heat is only conducted from the heating passages 74,76, to the upper surface 84 of the lower extrusion, rather than being conducted away into the supporting ground surface 86 beneath the assembly. The upper surface 84 of the lower extrusion forms the lower surface of a curved, venturi shaped air duct 88 which has an inlet 90, beneath the outer edge of the foot tread 102, and an outlet 92 at the inner end of the foot tread. Since the heated region is located towards the inner end, natural convection will cause the air to flow through the assembly, in the direction of the arrows A. This action is assisted by the"venturi"shape, whereby the relatively wide inlet end 90 of the passage first narrows down to a"throat"94, and then becomes progressively wider, towards the outlet 92.

The upper extrusion 72 is also filled with foam 96 as an insulator, and has thermal breaks 98, 100 formed after it is filled with foam, so that the foot tread surface 102 is isolated from the heating effect of the base of the structure, and the heated air passing through it.

Although it is shown in a horizontal orientation, it can also be used in a vertical position attached to a wall if required. For example it may be arranged to form a continuous"dado rail"around a room.

It will be appreciated that the principle of the invention can also be put into practice in alternative modes using different methods of insulation. For example, the internal duct walls can be connected to the outer casing by means of support members which are formed separately from a suitable material with heat insulating characteristics, such as a plastics material.

One example of such a construction is shown in Figure 7 which illustrates an arrangement in which two heating modules 120,122 are stacked on top of one another and connected by connectors of the type described above with reference to Figure 3.

Internal air ducts are formed in this construction, by means of pairs of extruded plates 124,126 which are mounted on flanged bracket assemblies 128, 130 of suitable heat insulating plastics material.

Baffles 140,142 of heat insulating plastics material are mounted on the inner faces of the outer casing and the outer sides of the duct plates 124,126 to reduce the transmission of heat to the outer casing.

In order to further insulate the outer casing from the heated air inside the ducts, the gaps between the upper and lower edges 132,134 of the plates and the corresponding edges 136,138 of the outer casing may also be closed by means of suitable gaskets of plastics material (not shown). In other respects the embodiment of Figure 7 operates in a similar way to that of Figure 5.

Figure 8a illustrates some further alternative features of a horizontal heating device of the general kind shown in Figure 6.

In this case the lower extrusion 160 is formed with an additional tube 162 which is pressurised with air in use, and has slots 164 opening into the inlet end of the air passage 166 which are arranged so as to assist the desired direction of airflow. The air passage 166 may also incorporate fins 150 in the form of flat plates shaped to match the internal profile of the passage, which are mounted on a transversely extending rod 168.

This construction is shown in more detail in Figure 8b. The rod 168 may form part of the support structure or it may be removed after assembly.

The top plate of the heating device may also be hinged below the inner edge 170 so that the outer edge 172 can be lifted for access to the interior, e. g. for cleaning. In the closed position the top plate is supported by spacers 152 which are also positioned by means of the rod 168.

As shown in Figure 8a, the base extrusion may also contain a housing 154 for a thermal cutout and for other wiring. Alternatively a shown in Figure 9, a printed film type heating element 156 may be mounted in contact with the underside of the top surface of the lower extrusion so as to provide direct heating of the metal, and similarly, a further printed element (not shown) can be mounted behind the lower surface of the upper extrusion to increase the heating effect. Figure 9 also illustrates the possible arrangement of an additional stiffening member 170, in the form of a polycarbonate I- beam which is fitted between the upper and lower internal surfaces to reinforce the structure whilst maintaining its insulating properties.

In order to provide an additional energy saving feature, it is also envisaged that the lower extrusion may be filled with a composite heat storage material so that the device can be heated by cheap rate off peak electricity.

It will, of course, be appreciated that the type of structure shown in Figures 6,8 and 9 can be utilised in various different environments where a relatively flat construction is required. For example, it can be incorporated in window sills, as indicated in Figures 8 and 9, so as to act as a combined heating and de-misting device, and thereby avoiding the necessity of attaching panel radiators to the wall surface below a window.

Referring to Figure 10, a further type of perimeter floor heating arrangement is shown in a raised computer floor installation in which the heater structure 172 is suitably supported on adjustable pedestals 174 so as to bring it to the same level as the floor 176.

The heater structure 172 comprises a base formed from two separate hollow extrusions 178 and 180 which are interconnected by a moulded plastics strip 182 forming a thermal break between them. As will be clear from the drawing, the strip and the two extrusions are formed with mating interlock cross-sections so that after assembly, they effectively form a single unit which comprises two thermally-isolated sections. The larger section 178 is formed with integral heater tubes 184, 186 for water or electric heating, in a similar way to the above described embodiments, and also a housing 188 for ancillary wiring for example to supply electric heating elements.

Alternatively, instead of incorporating separate heater tubes 184,186, the whole of the hollow interior of the extrusion 178 may be utilised as a larger capacity waterway.

The smaller section 180 is arranged to provide service trunking so that the unit can additionally act as a housing for electrical socket outlets 190, or it may be adapted to provide a passageway for fresh or conditioned air. For this purpose an air slot 192 is provided which communicates with the"throat"of the venturi inlet of the main air passage. A further or alternative such air passage 194 may also be provided at the rear of the larger extrusion with an air slot 196 communicating with the outlet end of the heating air passage of the unit.

As in the case of the embodiment of Figure 9, the top plate 196 of the unit is hinged at its rear edge 198 so that it can be opened for maintenance purposes. In the arrangement shown, the pivot for the hinge is formed by rounded projections 200 on the upper edges of a series of heat diffusion fins 202 which are arranged at intervals along the structure. These cooperate with corresponding slots in the edge of the cover plate, so that it is supported at regular intervals along its length.

As described with reference to the previous embodiments, the top plate 196 may be covered with a suitable insulating material to present a relatively cool outer surface.

The extrusion structure of Figure 10 may also be deployed in various other situations such as are illustrated in Figures 11,12 and 13. Figure 11 shows an integrated windowsill application in which the upper surface is covered with a moulded material such as MDF to give the impression of a timber sill, while at the same time providing insulation of the internal air passage from the outer face. As indicated by the arrows"A", cool air is drawn in under the sill edge by the venturi effect of the heating passage and after heating, leaves through the top grille 206. In this arrangement is is possible to provide a useful demisting or anti-condensation effect for the window glass 208.

Figure 12 shows an alternative arrangement for an existing sill 210, in which the heating unit 212 is positioned in a vertical plane against the wall below the sill edge, while Figure 13 shows a"dado-heating"arrangement in which the unit 212 is installed vertically part way up a wall, with a hollow"handrail-shaped"trunking member 214 superimposed on its top edge. This trunking can then provide additional electrical cabling capacity.

The construction of the dado heater is shown in more detail in Figure 14a, which show in dotted lines 216 how a wiring connection is made between a trunking compartment inside the handrail 214, and a socket outlet 218 mounted on the front face of the heating unit. As show in more detail in Figures 14b and 14c, the heater construction also includes an extra conduit 180 (as in the arrangement of Figure 10 above) with air slots 192 which allow additional fresh or conditioned air to be supplied to the ends of the unit. In order to control the distribution of the air along the length of the unit, the slots 192 may be arranged, as shown in figure 14c, with a slideable vent arrangement so that the slots can be selectively opened and closed. The slideable vents may for example be moulded plastic strips which engage in the slots and can be slid across to open or close them in a conventional manner. It will be appreciated that such an arrangement can also be incorporated in any of the other above-described embodiments.

It will also be appreciated that a number of such alternative features have been particularly described in connection with specific embodiments above. However, in practice, it will be clear that they may be incorporated in other embodiments in a variety of possible combinations.