Field of the Invention

The present invention relates to an apparatus for drying and/or styling the hair of a person (or conceivably an animal), for example after washing the hair or as part of a styling process.

The applicant has previously described in WO2021/019239, an apparatus for drying and styling hair, the disclosure of which is incorporated herein in its entirety by reference.

The applicant has made further developments relating to this device. Some of these developments are specific to the device whilst some are more generally applicable to any hair styling device.

Summary of the Invention

The present invention provides a hair styling device comprising: an elongate first arm having a distal end with at least one plate and a proximal end; and an elongate second arm having a distal end with at least one plate and a proximal end; wherein the proximal end of the second arm is coupled to the first arm by a hinge so that the first and second arms are moveable between an open position in which hair can be introduced between the distal end of the first arm and the distal end of the second arm and a closed position in which hair is clamped between the distal end of the first arm and the distal end of the second arm; wherein the hinge is coupled to the first arm at a position that is offset from the proximal end of the first arm and wherein a ratio of a distance between the hinge and the proximal end of the at least one plate at the distal end of the first arm and a distance between a centre of gravity of the hair styling device and the proximal end of the at least one plate at the distal end of the first arm lies within the range 0.25 and 0.4.

In one embodiment, the ratio of the distance between the hinge and the proximal end of the at least one plate at the distal end of the first arm and the distance between the centre of gravity of the hair styling device and the proximal end of the at least one plate at the distal end of the first arm lies within the range 0.28 and 0.35.

The present invention further provides a hair styling and drying device, comprising: a housing having an air inlet through which air can be drawn and at least one air outlet through which air can be output; and a fan mounted within the housing and configured to draw air into the housing through the air inlet and to blow the air towards the air outlet; wherein the housing comprises first and second housing parts that are coupled together and wherein a sealing member is provided to prevent the ingress of water into the housing at a joint between the first and second housing parts. Preferably, the device comprises first and second mutually- opposing arms adapted for movement between an open configuration for receiving a length of wet hair therebetween and a closed configuration adjacent the hair, such that, in use, when the arms are in the closed configuration they form an interarm chamber across which the hair passes.

In one embodiment, the first arm further comprises a heater for heating air from the fan before it is output into said inter-arm chamber. The device may also comprise mutually-opposing plates disposed on the first and second arms, the mutually-opposing plates being arranged to come together when the first and second arms are in the closed configuration. Typically, first and second plates are disposed on the first arm, and respective opposing first and second plates are disposed on the second arm. In some embodiments, at least one of said plates comprises means for applying heat to said length of hair in use, when the first and second arms are in the closed configuration.

The sealing member may comprise a seal that extends around and is sandwiched between a rim of the first housing part and a rim of the second housing part. In other embodiments, the sealing member comprises a water resistant or waterproof overmold that covers the joint between the first and second housing parts when coupled together. Alternatively, the sealing member comprises a water resistant or waterproof sleeve that fits over the first and second housing parts when coupled together. The present invention further provides a hair styling device comprising: a housing having an air inlet through which air can be drawn and an air outlet through which air can be output; a fan mounted within the housing and configured to draw air into the housing through the air inlet and to blow the air towards the air outlet; a heater mounted within the housing downstream of the fan; and an impeller mounted within the housing downstream of the heater for mixing the air prior to being output from the air outlet.

In one embodiment, the impeller is passive and rotates due to the flow of air passing through the housing from the air inlet to the air outlet. In an alternative embodiment, a motor may be provided to rotate the impeller. Typically, the motor is also used to rotate the fan used to draw air into the housing through the air inlet. However, in other embodiments, the motor may operate independently of the fan.

In one embodiment, the air inlet is annular in shape and is defined by a gap between a spigot that protrudes through the air inlet beyond a distal end of the air inlet and the housing of the hair styling device.

The air inlet may comprise a filter that connects between the housing and the spigot and that tapers from the connection with the housing to the connection with the spigot. The housing may be elongate having a longitudinal axis and the air inlet is oblique to the longitudinal axis.

The present invention also provides a method of styling hair characterised by using any of the above described devices.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which:

Figure 1a is a perspective overview of a combined hair dryer/styler device comprising mutually-opposing drying/styling arms in an open configuration, with each arm incorporating a pair of heater plates and an airflow guide structure;

Figure 1 b shows the device of Figure 1a with the arms in a closed configuration; Figure 1c illustrates the device of Figure 1 in use;

Figure 2 is a perspective longitudinal cross-sectional view of the lower arm of the device shown in Figure 1 , illustrating the main internal components of the device and the air flow within the device during use;

Figure 3 is a side cross-sectional view of the distal end of the lower arm shown in Figure 2 and illustrating directions of airflow through the distal end of the lower arm;

Figure 4 is a transverse cross-sectional view through the arms of the device of Figure 1 in the closed configuration, and also illustrating directions of airflow;

Figure 5 is a side cross-sectional view of the distal end of the lower arm of the device shown in Figure 1 showing design features that help to mix the air before the air is output towards the user’s hair;

Figure 6 is a side cross-sectional view of a modified arrangement for mixing the air that includes an additional impeller for mixing the air prior to output to the user’s hair;

Figure 7a is a side cross-sectional view of the device of Figure 1 illustrating the position of a hinge that connects the upper arm to the lower arm relative to a centre of gravity of the device;

Figure 7b is a side cross-sectional view of the device of Figure 1 illustrating the range of positions of the hinge relative to the centre of gravity that has been found to result in a device having good ergonomics;

Figure 8a is an exploded view of the lower arm of the device shown in Figure 1 , that illustrates a U-shaped seal that is provided to prevent the ingress of moisture into the housing of the lower arm;

Figure 8b is a transverse cross-sectional view illustrating the way in which the U- shaped seal seals off the junction between the two housing halves;

Figure 9a and 9b are transverse cross-sectional views of an alternative way of sealing the junction between the two halves of the lower arm housing; and

Figure 10 is an exploded view of a further alternative way of preventing the ingress of moisture into the housing of the lower arm.

In the figures, like elements are indicated by like reference numerals throughout. Detailed Description of Preferred Embodiments

The present embodiments represent the best ways known to the applicant of putting the invention into practice. However, they are not the only ways in which this can be achieved.

Overview of Device

Figure 1a is a perspective overview of a combined hair dryer/styler device 10 according to a first embodiment, with arms 14, 16 in an open configuration, and Figure 1b shows the same device 10 with the arms 14, 16 closed (as in use, e.g. as shown in Figure 1c). Figures 2-4 show further views of parts of the device 10, with Figures 3 and 4 showing air flow through the device 10 in use.

Referring initially to Figures 1a and 1 b, the device 10 is an all-in-one handheld device that can be used to dry hair in a quick and easy manner, whilst also enabling styling of the hair (e.g. to straighten the hair, or to add “body and volume” to it).

The device 10 comprises first and second mutually-opposing arms 14, 16 arranged in a broadly similar manner to the arms of a handheld hair styler. The first arm 14 has a main body portion 12 at a proximal end 92 of the arm 14 and a hair treating distal end 93. The second arm 16 is coupled at its proximal end 94 to the first arm 14 and has a hair treating distal end 95. The first and second arms 14, 16 are adapted for movement between an open configuration (as shown in Figure 1a) for receiving a length of wet hair therebetween, and a closed configuration (as shown in Figure 1 b) adjacent the hair, to create tension in the hair, such that, in use, when the arms 14, 16 are in the closed configuration they form an inter-arm plenum chamber (13, Figure 4) across which the hair passes.

Figure 2 is a perspective view of the body part 12 of the lower arm 14 with half of the housing removed to expose the main components mounted within the body part 12. As can be seen in Figure 2, the body part 12 houses a fan assembly 38 at the proximal end 92 of the body part 12, for drawing air (represented by the arrows 73) into the body part 12 through an air inlet 60 and for forcing the air along the body 12 towards the distal hair treating end of the lower arm 14. The air inlet 60 is formed as an annular opening around a spigot 63 (shown in Figure 1 ) which extends out beyond the proximal end 92 of the body part 12. The spigot 63 therefore makes it difficult for items to close off the entire air inlet 60. Additionally, the proximal end 92 of the body part 12 is also preferably sloped relative to the longitudinal axis of the body part 12, as this also helps to reduce the likelihood of the entire air inlet 60 being blocked. The fan assembly 38 has an impeller and is typically also provided with a filter 65 for preventing dust and debris from reaching the fan assembly 38.

The air from the fan assembly 38 is heated by a heater 30 before being directed into the distal end 93 of the lower arm 14 where an air-flow guide structure 24 (that is shown in more detail in the cross-sectional view of Figure 3) guides the air towards the user’s hair. More specifically, and as shown in Figure 3, the heated air from the heater 30 passes along the distal end 93 of the lower arm 14 in a direction D1 that is substantially parallel to the length of the arm 14 and the airflow guide structure 24 causes the air to change direction to a second direction D2, that is from the arm 14 towards the opposing arm 16, i.e. inwards into an inter-arm plenum chamber 13 formed by the arms 14, 16 in the closed position (which is shown in Figure 4). The heater typically takes the form of an electrically- powered heating coil (or other electrical heating elements), that is operable to heat the air drawn in by the fan assembly 38.

As illustrated by the circuit board 36 shown in Figure 2, control electronics 37 are mounted within the body part 12 between the fan assembly 38 and the heater 30. This allows the incoming air to keep the control electronics 37 cool during use. Electrical power is provided to the device 10 via a power cord 64 which typically connects to an AC mains power supply. However, in an alternative embodiment the device 10 may be powered by one or more DC batteries or cells (which may be rechargeable, e.g. from the mains or a DC supply via a charging lead), thereby enabling the device 10 to be a cordless product. The control electronics 37 control the operation of the device 10. As shown in Figure 1a, a control button or switch 23 may be provided on the device 10, to enable it to be turned on or off, and the control electronics 37 can control the switching on and off of an indicator light to show whether the power is on. The control electronics 37 can also cause a sound generator (not illustrated) to play out a sound when the device 10 is switched on and ready to use.

As illustrated for example in Figure 1a, the second arm 16 is coupled to the body part 12 of the first arm 14 by means of a hinge 18, by virtue of which the first and second arms 14, 16 are movable relative to one other (in the illustrated embodiment, by moving the second arm 16 towards and away from the first arm 14). Thus, the first and second arms 14, 16 can be brought together, into the closed configuration (as shown in Figure 1b), or moved apart, into the open configuration (as shown in Figure 1a), by a user in use. In the illustrated embodiment, each of the arms 14, 16 widens relative to the body part 12 to form a “head” of the device 10, distal from the body part 12, although other embodiments are possible in which the head does not widen in the illustrated manner.

The hinge 18 can incorporate any suitable means for allowing the first and second arms 14, 16 to be moved relative to one other. Preferably the hinge 18 also incorporates spring means configured to bias the first and second arms 14, 16 into the open configuration, such that the user is required to apply pressure to the arms 14, 16 to close them together (overcoming the effect of the spring means), and such that the arms 14, 16 automatically open, under the effect of the spring means, once the pressure is removed. For example, the hinge 18 may incorporate a leaf spring or a coiled spring.

The hinge 18 and the spring means can be one and the same. For example, the spring means itself can be used to couple the second arm 16 to the body part 12, thereby avoiding the need to provide a separate mechanical hinge and simplifying the overall construction of the device 10.

As shown in Figure 1a in the illustrated embodiment the inner surface of the first arm 14 incorporates first and second elongate heater plates 20a, 20b, extending along the length of the arm 14 either side of the airflow guide structure 24. The second arm 16 also incorporates first and second elongate heater plates 22a, 22b (not visible in Figure 1a, but shown for example in Figure 4) in corresponding positions to heater plates 20a and 20b. Each of the heater plates 20a, 20b, 22a, 22b is provided with a respective electrical heating element, operable to cause the respective heater plate to heat up. In the illustrated embodiment the operating temperature of the heater plates 20a, 20b, 22a, 22b is typically around 120-130°C.

The first and second arms 14, 16 and the first and second heater plates on each arm 20a, 20b, 22a, 22b are arranged such that, when the arms 14, 16 are in the closed configuration, the first and second heater plates 20a, 20b of the first arm 14 come into contact with the first and second heater plates 22a, 22b of the second arm 16. Preferably the heater plates 20a, 20b, 22a, 22b are made of a material having relatively high thermal conductivity, and are preferably provided with one or more temperature sensors (e.g. a temperature sensor for each plate, or one or more temperature sensors that each serves a plurality of heater plates) for sensing the temperature of the heater plate. The sensed temperatures are then fed back to the control electronics 37 so that the control electronics 37 can control the power delivered to the heater plates 20a, 20b, 22a, 22b to maintain them at a desired operating temperature.

The heater plates 20a, 20b, 22a, 22b serve a number of purposes during use of the device 10. Firstly, with the user having sandwiched a length of wet hair between opposing plates 20a and 22a, and between opposing plates 20b and 22b (i.e. transversely across the plenum chamber 13 formed by the first and second arms 14, 16 in the closed configuration), and by drawing the device 10 along the length of wet hair, the heater plates 20a, 20b, 22a, 22b subject the wet hair to a squeegeeing effect, removing excess unbound water, and also heat the hair to promote subsequent evaporation of the water. Secondly, the heating provided by the heater plates 20a, 20b, 22a, 22b causes the walls of the plenum chamber 13 to be heated (via thermal conduction), and also helps maintain the temperature of the airflow delivered through the plenum chamber 13 by the fan assembly 38. Thirdly, the heater plates 20a, 20b, 22a, 22b can be used to style the hair, as an integral part of the drying process. The heater plates 20a, 20b, 22a, 22b are preferably configured as ceramic float plates with springs having a low spring rate or stiffness, thereby giving good control of hair tension.

Allowing for the airflow heating coil (or other heater elements) and the heater plates 20a, 20b, 22a, 22b, as well as the fan assembly 38, the overall power consumption of the device 10 is around 600-800 W, which is significantly less than a 2000 W conventional hairdryer. Of course, higher powered motors could be used in the device 10 which would increase the power consumption but would allow the device 10 to dry the user’s hair more quickly.

Turning now to Figure 4, this illustrates further directions of airflow though the arms 14, 16 of the device 10 when viewed in transverse cross-section, facing towards the body part 12 of the device 10.

Starting in the centre of Figure 4, the air flowing from the lower arm 14 in direction D2 can be seen entering the inter-arm plenum chamber 13 from an airflow conduit 15 via the cells of the airflow guide structures 24. Some of the air will bounce off the user’s hair whilst some will pass into the other arm 16. Upon leaving the interarm chamber 13, the air spreads sideways and enters the airflow redirecting channels 28, from which the air then passes along airflow conduits 19a, 19b, 21a and 21 b to leave the device 10 via vents 26 in directions D3 (via conduits 19a and 21a) and D4 (via conduits 19b and 21 b). As shown in Figure 4, airflow conduits 19a, 19b, 21a and 21 b respectively extend behind the heater plates 20a, 20b, 22a and 22b that are mounted on the first and second arms 14, 16. Advantageously, the vents 26 direct the outgoing air towards the roots of the hair, to dry the roots and create root lift.

The device 10 described above has been found to provide efficient drying and styling of the user’s hair. The combination of conductive heating of the hair by the heater plates 20a, 20b, 22a and 22b and the convective heating of the hair in the enclosed chamber 13 by the heated air flow significantly increases the drying efficiency of the device 10 over conventional hot air devices. The inventors have made a number of improvements to the device 10 described above and these will now be described below.

Airflow mixing improvement

In the device 10 described above, a heater 30 is provided within the body part 12 to heat the air before it is fed into the lower arm 14. As explained in the applicant’s earlier PCT application WO2021/019239, such heaters are typically formed by a resistive coil that is coiled inside the housing. As illustrated in Figure 5, the conductive parts of the coil 71 tend to be located at the periphery of the air flow conduit through which the air passes. This results in the heater 30 producing an annular ring of hotter air surrounding a cooler stream of air in the middle. This hotter air and cooler air have to be mixed to prevent wide variations in the temperature of the air that is blown onto the user’s hair. In the applicant’s earlier PCT application, an airflow mixer 34 was provided at the outlet of the heater 30 to push the cooler air in the centre towards the hotter air around the perimeter thereby helping to mix the hot and cooler air together.

The applicant has found that, and as illustrated in Figure 6, improved mixing of the air can be achieved by providing an impeller 68 in the air flow channel after (downstream of) the heater 30. In this example, the impeller 68 is passive - that is to say that it is unpowered and simply rotates due to the stream of air passing by the impeller 68. As the impeller 68 rotates, it mixes the air output from the heater 30 which helps to ensure a uniform air temperature of air at the output of the air flow guide structure 24 in the lower arm 14, thereby achieving uniform drying across the hair section within the chamber 13.

As those skilled in the art will appreciate, the additional impeller 68 can be provided without the mixer 34. However, the combination of the mixer 34 and the impeller 68 is preferred as it provides improved mixing of the air. Additionally, instead of using a passive impeller 68. A motorised impeller 68 could be provided instead. In this case, the motor that drives the impeller 68 may be separate from the motor used to turn the fan assembly 38 or the same motor could be used. If the same motor is used, then a drive shaft would need to extend between the motor and the fan assembly 38 and the motor and the impeller 68. The motor itself could be positioned inside the heater coil (in the region where cooler air passes through the heater) or it may be positioned upstream of the heater 30 to prevent the motor over-heating.

As is illustrated in Figures 5 and 6 and as described in the applicant’s earlier PCT application mentioned above, an air splitter 52 is preferably also provided at the inlet of the heater 30 to direct the incoming air towards the heater coil at the periphery of the heater 30. The inventors have found that particularly good mixing of the air stream is achieved using the combination of the splitter 52, the mixer 34 and the additional impeller 68.

Hinge Position Improvement

As discussed above, the upper arm 16 is coupled to the body 12 of the lower arm 14 at the hinge 18. An important aspect of the design of the device is the position of the hinge along the body 12 relative to the centre of gravity (or centre of mass) of the device 10, as this affects the ergonomics of the device 10. In particular, if the hinge 18 is too far back towards the proximal end 92 of the body part 12 or too far forward towards the distal end 92 of the body 12, then the device 10 can feel unbalanced when held and operated by the user. In the device 10 illustrated in Figure 1 , the hinge 18 is located about 147mm from the proximal end of the heater plates 20 mounted on the lower arm 14 and the centre of gravity is located about 43mm from the same point on the heater plates 20. The inventors have found that this spacing provides for a highly ergonomic arrangement of the hair styling device 10 - allowing the user to be able to rest the body 12 in the user’s fingers close to the centre of gravity whilst the user’s palm extends round the body 12 so that the user’s thumb can extend along the upper arm 16 - thereby making it easy for the user to apply the necessary force to move the arms 14, 16 into their closed configuration.

Figure 7a illustrates the location of the hinge 18 and the location of the centre of gravity (represented by the symbol 72). The line marked A in Figure 7a represents the plane that is perpendicular to the longitudinal axis of the hair styler 10 that passes through the most proximal point of the heater plates 20. The line marked B in Figure 7a represents the plane that is perpendicular to the longitudinal axis of the hair styler 10 that passes through the centre of the hinge 18. The line marked C in Figure 7a represents the plane that is perpendicular to the longitudinal axis of the hair styler 10 that passes through the centre of gravity 72. The distance between the hinge and the most proximal point of the heater plates 20 can be approximated by the perpendicular distance (AB) between planes A and B; and the distance between the same point of the heater plates 20 and the centre of gravity can be approximated as the perpendicular distance (AC) between planes A and C.

In the preferred embodiment, the distance AB is approximately 147mm and the distance AC is approximately 43mm. As those skilled in the art will appreciate, the ergonomic benefits described above can be achieved without using these exact locations. The inventors have found by experiments that the following range of possible distances provide for good ergonomics of the device:

Thus, the minimum ratio of AB to AC can be determined from:

ABmin/ACmax

And the maximum ratio of AB to AC can be determined from:

ABmax/ACmin Thus, the inventors have found that to achieve the ergonomic benefits discussed above requires the ratio of AB:AC to be between 0.25 and 0.40 and preferably between 0.28 and 0.35.

Water Sealing Improvement

As discussed above, the device 10 is designed to be able to dry and style wet hair. When drying wet hair with the device described above, significant amounts of water will be removed from the hair within the enclosed chamber 13 of the device. Much of that water will be vented with to the surrounding atmosphere. However, some of that water will condense within the heads of the upper and lower arms 14, 16 or on the outer surface of the device 10. Since the device 10 has various electrical connections and exposed resistive heater windings 71 within the body 12, it is important to minimise the risk of water getting back inside the housing of the body 12. The flow of air passing along the lower arm should prevent water from travelling back via the airflow conduit 15. However, the inventors have found that it is possible for moisture to get into the interior of the body part 12 via the split lines between the two body halves 12a, 12b that form the housing of the body part 12. This is because the two housing halves 12a and 12b are made substantially of rigid materials with which it is difficult to form a water-tight seal. The inventors have therefore designed the two housing halves 12a and 12b so that a seal can be provided to seal the junction between the two halves 12a, 12b.

Figure 8 illustrates one example of a seal that can be used. In this example, a II- shaped seal 84 extends around the junction between the first body half 12a and the second body half 12b. As shown in the cross-sectional view of Figure 8b, the edges of the two body halves 12a, 12b are designed to interlock and to provide an internal groove in which the flexible seal 84 can be mounted.

The U-shaped seal 84 may be made of various appropriate materials for the purposes of sealing the junction between the two housing halves 12a and 12b, such as rubber, expanding foam, or plastic. Figure 9 illustrates an alternative solution in which an overmold 88 is applied at the junction between the two body halves 12a and 12b. Since the overmold 88 is applied to the junction from the outside once the two housing halves 12a and 12b are assembled together, the lip at the edge of each body half 12a, 12b preferably defines a groove in the outer surface in which the overmold 88 can be applied.

The overmold 88 may create the watertight seal via a significant overlap between the overmold 88 and the two body halves 12a, 12b. Alternatively, the overmold 88 may create a watertight seal via a thermal joining process in which the material of the overmold 88 is partially melted to seal off the joint between the two housing halves 12a and 12b.

The overmold 88 may be made of various appropriate materials for the purposes of waterproofing such as plastic or silicon.

Figure 10 illustrates an alternative solution to the sealing problem, that uses a nonremovable sleeve 90 that is fitted over the two body halves 12a, 12b once the two halves have been assembled, thereby covering the seam or joint between the two body halves 12a and 12b. The sleeve may be made of a plastics material (such as polythene or PVC) that shrinks under the application of heat to seal off the joint. Alternatively, the sleeve 90 may be formed of an elastic and waterproof material (such as a polyester based plastics material) that can stretch over the two body halves 12a and 12b when assembled. This water seal can be used in other hair styling devices including devices having a single arm - such as a paddle brush or the like.

Modifications and alternatives

Detailed embodiments and some alternatives have been described above. As those skilled in the art will appreciate, a number of modifications and further alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. It will therefore be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.

In the embodiments described above, the first arm 14 contains an airflow conduit 15 and is provided with an airflow guide structure 24. However, in alternative embodiments, both of the arms 14, 16 may be provided with an airflow conduit and airflow guide structure 24.

In the embodiments described above, heater plates are provided symmetrically on either side of each arm 14, 16. However, as those skilled in the art will appreciate, it is not necessary that both these plates be heated, and in alternative embodiments only one plate may be heated, or neither of the plates may be heated. The squeegeeing effect of the plates may be sufficient in some circumstances to dry the hair in combination with the airflow, without either or both the plates being heated. Furthermore, unheated plates may be used to apply tension to the hair to provide a degree of styling. However, having at least one heater plate is preferred as it helps with the drying/styling process. Moreover, using a pair of heater plates, as in the embodiments described above, advantageously allows for bidirectional/ambidextrous use of the device.

Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “containing”, means “including but not limited to”, and is not intended to (and does not) exclude other components, integers or steps.

It is desirable that the styler product should have substantially the same performance wherever it is used around the world, even though mains voltages may vary from country to country. Mains voltage variation particularly impacts the temperature of the heated air within the device, since the air is heated using a standard resistive wire heater, and the electrical power consumed by such a heater and converted to heat is a function of voltage. It is therefore desirable to ensure that the energy transferred to the air is the same, regardless of the location of the device around the world, to ensure that the drying rate is the same and the product does not damage the hair fibre.

Control of energy transfer to the air can be achieved in various ways - for example, by varying the fan speed (which is undesirable since it affects the amount of airflow), or by using a variable resistor in the heater (which is also undesirable). Another option, which the inventors have found to work well, is to control the temperature of the heater by means of an electrical switching technique, whilst keeping the fan speed constant. For instance, the number of mains cycles across the heater per second may be controlled using a standard zero-crossing switching technique employing triacs, essentially performing pulse width modulation of the electrical power supplied to the heater. In such a manner the thermal output of the heater element, and the device more generally, can be controlled irrespective of variations in local mains voltage.