WO2019231394A1

WO2019231394A1 - An instant heater

Info

Publication number: WO2019231394A1
Application number: PCT/SG2018/050273
Authority: WO
Inventors: Khoon Hua TAN; Sin Khow CHEW
Original assignee: Tan Khoon Hua; Chew Sin Khow
Priority date: 2018-06-01
Filing date: 2018-06-01
Publication date: 2019-12-05

Abstract

An instant heater for heating water is provided. The heater includes an inlet adapted to channel water into the heater; an outlet adapted to channel water out of the heater; a heating channel in fluid communication with the inlet and the outlet, wherein the heating channel is adapted to heat the water from the inlet and channelled therethrough and the heated water is channelled from the heating channel out of the heater via the outlet, wherein the heating channel comprises a duct in fluid communication with the inlet and outlet; and a heating strip extending alongside and outside the duct, wherein the heating strip is thermally connected to the duct and is adapted to heat the water flowing therethrough; a flow valve disposed between the heating channel and the inlet, the flow valve adapted to control the flow of the water into the heating channel.

Description

An Instant Heater

Field of Invention

[0001] The present invention relates to an instant heater. For example, the present invention relates to a tankless instant heater.

Background

[0002] Water heaters are commonly used in residential and commercial places to provide heated water. Water heaters may be categorised into at least four categories, of which two categories are instant water heaters and storage tank water heaters. Water heaters are commonly used in households to provide heated water. For example, water heaters are used in bathrooms to heat up water for bathing, especially in temperate countries. In another example, water heaters are used for providing heated water for drinking or cooking.

[0003] The conventional instant heater typically includes a small heating tank with a heating element within its enclosure to contain water to be heated. Therefore, the conventional instant heater, while is known as a tankless heater, has a heating tank therein with a heating element within the tank to heat the water. The storage tank water heater includes a tank for containing water to be heated. Typically, the storage tank water heater has a tank of about 25 litres, which is considerably larger than the tank in the instant heater, which can be no larger than a 1 litre tank. In both cases, the water is stored and held in the tank to be heated before being discharged from the water heater.

[0004] Typically, the instant heater has a relatively high-power consumption, e.g. 3,000W- l2,000W. Compared to a washing machine that consumes about 2,000W and a kettle that consumes about 1800W, the instant heater has a much higher power consumption. Therefore, as there have been instances of electrical leakages, users are concerned about electrocution when using a water heater of such high power. [0005] Therefore, it would be advantages to be able to provide an instant heater that overcomes the above disadvantages, i.e. safer, lower power consumption, tankless configuration and safe for use.

Summary

[0006] According to various embodiments, an instant heater for heating water is provided. The heater includes an inlet adapted to channel water into the heater; an outlet adapted to channel water out of the heater; a heating channel in fluid communication with the inlet and the outlet, wherein the heating channel is adapted to heat the water from the inlet and channelled therethrough and the heated water is channelled from the heating channel out of the heater via the outlet, wherein the heating channel comprises a duct in fluid communication with the inlet and outlet; and a heating strip extending alongside and outside the duct, wherein the heating strip is thermally connected to the duct and is adapted to heat the water flowing therethrough; a flow valve disposed between the heating channel and the inlet, the flow valve adapted to control the flow of the water into the heating channel.

[0007] According to various embodiments, the duct may have an internal depth of 1.6- 2.2mm.

[0008] According to various embodiments, the duct may have an internal depth of 1.5-2mm.

[0009] According to various embodiments, the duct may have an internal depth of 1.6- 1.8mm.

[0010] According to various embodiments, the instant heater may further include an inflow chamber disposed between and in fluid communication with the heating channel and the inlet.

[0011] According to various embodiments, the inflow chamber may include an inflow opening in fluid communication with the inlet and an outflow opening in fluid communication with the heating channel, such that the inflow opening is misaligned from the outflow opening. [0012] According to various embodiments, the inflow chamber may include a spout extending from the inflow opening into the inflow chamber, wherein the spout is adapted to direct the water away from the outflow opening.

[0013] According to various embodiments, the instant heater may further include an outflow chamber disposed between and in fluid communication with the heating channel and the outlet.

[0014] According to various embodiments, the duct may include a U-shaped profile, wherein the duct may be a U-shaped elbow with a first side channel and a second side channel extending from each end of the U-shaped elbow, such that the first side channel is in fluid communication with the inlet and the second side channel is in fluid communication with the outlet. The heating strip may include a first heating surface and a second heating surface behind the first heating surface, such that the first side channel is in thermally connected to the first heating surface and the second side channel is thermally connected to the second heating surface.

[0015] According to various embodiments, the U-shape elbow may include a reservoir adapted to contain water from the first side channel and the second side channel.

[0016] According to various embodiments, the heating strip may be spaced from the duct.

[0017] According to various embodiments, the heating strip may be made of silicon nitride.

[0018] The instant heater as shown provides a tankless heating configuration, i.e. no tank required in the heater. Further, the heating element, i.e. the heating strip, in the instant heater is segregated from the water so as to prevent any possibility of electrical leakage from the heating element to water, thereby eliminating any risk of electrocution.

Brief Description of Drawings

[0019] Fig. 1 shows a schematic diagram of an example of a tankless instant heater. [0020] Fig. 1A shows a sectional view of the heating channel along line A-A in Fig. 1.

[0021] Fig. 2 shows a schematic diagram of an example of the tankless instant heater.

[0022] Fig. 2A shows a sectional view of an example of the inflow chamber along line B-B in Fig. 2.

[0023] Fig. 3 shows a schematic diagram of an example of the tankless instant heater.

[0024] Fig. 4 shows a schematic diagram of an example of the tankless instant heater.

[0025] Fig. 5A shows an enlarged view of an example of the inflow chamber.

[0026] Fig. 5B shows an enlarged view of an example of the outflow chamber.

[0027] Fig. 6 shows an enlarged view of an example of the inflow chamber.

[0028] Fig. 7 shows a schematic diagram of an example of the tankless instant heater.

Detailed Description

[0029] Fig. 1 shows a schematic diagram of an example of an instant heater 100 for heating water. Heater 100 includes an inlet 102 adapted to channel water into the heater 100, an outlet 104 adapted to channel water out of the heater 100, a heating channel 110 in fluid communication with the inlet 102 and the outlet 104, such that the heating channel 110 is adapted to heat the water from the inlet 102 and channelled therethrough and the heated water is channelled from the heating channel 110 out of the heater 100 via the outlet 104. Heating channel 110 includes a duct 112 in fluid communication with the inlet 102 and outlet 104, and a heating strip 114 extending alongside and outside the duct 112, such that the heating strip 114 is thermally connected to the duct 112 and is adapted to heat the water flowing therethrough. Instant heater 100 has a flow valve 108 disposed between the heating channel 110 and the inlet 102, the flow valve 108 adapted to control the flow of the water into the heating channel 110.

[0030] As shown in Fig. 1, the heater 100 is adapted to heat the water as it flows through it and does not contain a heating tank to temporarily hold the water to be heated by a heating element within the heating tank like a conventional instant heater, i.e. a tankless instant heater. By controlling the flow rate of the water into the heating channel 110, it is possible to control the speed of the water such that the water may be heated to the desired temperature before leaving the instant heater 100. In addition, the heating strip 114 is disposed outside of the duct 112 and does not contact the water flowing therethrough unlike the conventional instant heater where the heating element is within the tank and is in direct contact with the water therein.

[0031] Referring to Fig. 1, the heater 100 may include a housing 106 adapted to contain the heating channel 110. Heater 100 may include a first conduit 101 between the inlet 102 and the heating channel 110 and a second conduit 103 between the heating channel 110 and the outlet 104. Heater 100 may include an inlet valve (not shown in Fig. 1) adapted to control the flow of water into the heater 100. Instant heater 100 may include an outlet valve (not shown in Fig. 1) adapted to control the flow of water out of the heater 100. Heater 100 may be connected to a water source (not shown in Fig. 1) via the inlet 102. Water source may have a pressure of 3.5-5.0 bar, preferably 3.5-4.2 bar, preferably 3.8-4.0 bar, preferably 4 bar. Outlet 104 may be connected to a water point (not shown in Fig. 1), e.g. a tap, a hose, shower head, to supply the heated water. Housing 106 may be made of stainless steel or equivalent material.

[0032] Heating strip 114 may have a proximal end 114P and a distal end 114D opposite the proximal end 114P. Duct 112 may extend alongside the heating strip 114 from the proximal end 114P to the distal end 114D. While the duct 112 as shown in Fig. 1 has a linear profile, the duct 112 may have other profiles, e.g. wave, curved. Heating strip 114 may be shaped to correspond to the profile of the duct 112 accordingly. Water may be channelled into the heater 100 to be heated to a pre-determined temperature along the heating channel 110 before exiting the heater 100 via the outlet 104. As the water is being channelled from about the proximal end 114P to about the distal end 114D of the heating strip 114, the water is gradually being heated until the pre-determined temperature.

[0033] Flow valve may be configured to control the water flow at a pre-determined flowrate, e.g. 2.3 l/min-3.0 1/min. It is also advantageous to control the flow rate of the water to protect the internal components of the instant heater 100. When the flow rate is too high, e.g. 5 1/min, the speed of the water, and therefore its pressure, entering the instant heater 100 may damage it over a period of time. Therefore, it is possible to lengthen the life of the instant heater 100 if the speed of the water is control to within the design specification of the instant heater 100. Heater 100 may include a heat sensor (not shown in Fig. 1) at about the outlet 104 to sense the temperature of water flowing out of the heater 100 via the outlet 104. Heater 100 may include a controller (not shown in Fig. 1) connected to at least one of the following: the flow valve, the heat sensor, the inlet valve, the outlet valve and the heating strip 114. Controller may be configured to control the temperature of the heated water to a pre-determined temperature, e.g. 48°C, 40°C etc. Heating strip 114 may be turned off when or before the pre determined temperature is reached. Inlet valve and outlet valve may be a mechanical valve, electronic valve, pneumatic valve, etc. Controller may be configured to control the flowrate of the water so that the required temperature may be reached. Heater 100 may include a strainer (not shown in Fig. 1) disposed at about the inlet 102 to prevent impurities in the water supply from entering the heater 100. Strainer may be a 500-micron strainer.

[0034] Fig. 1A shows a sectional view of the heating channel 110 along line A-A in Fig. 1. As shown in Fig. 1A, the duct 112 may have an internal width W and an internal depth D. Duct 112 may extend along a longitudinal direction parallel to the heating strip 114. Duct 112 may include a heating surface 112H which is a surface of the duct 112 that conducts heat from the heating strip 114 to the water flowing through the duct 112. Width W may be measured across a section of the duct 112, i.e. in a direction perpendicular to the longitudinal direction and parallel to the heating surface 112H. Depth D may be measured in a direction perpendicular to the longitudinal direction and the heating surface 112H. Width W may the minimum distance of thermal contact between the duct 112 and the heating strip 114. Depth D may be the maximum internal distance of the duct 112 from its heating surface 112H or the maximum depth that the water flowing therethrough will be heated. Duct 112 may have a flat profile such that the width W may be multiple times the length of the internal depth D. Duct 112 may have an internal depth D of 2mm or less. Duct 112 may have an internal depth D of l.5-2mm. Duct may have an internal depth D of 1.6-1.8mm. Width W may be about 20mm, 25mm, 30mm, etc.

[0035] Fig. 2 shows a schematic diagram of an example of the instant heater 200. Same feature in different examples have the same last two digits in their reference numbers. As shown in Fig. 2, the instant heater 200 may include an inflow chamber 220 disposed between and in fluid communication with the heating channel 210 and the inlet 202. Inflow chamber 220 may have a cross-sectional area that is larger than that of the duct 212. As shown in Fig. 2A, the inflow chamber 220 may have a height longer than the depth D of the duct 212. Inflow chamber 220 may be adapted to provide a space to allow steam generated along the heating channel 210 to escape to. Referring to Fig. 2, the inflow chamber 220 may have an upper compartment 220U and a lower compartment 220L below the upper compartment 220U. As will be explained later, when the water supply to the heater 200 is stopped, the water in the inflow chamber 220 would be drained into the heating channel 210. Water may be trapped in the lower compartment 220L while any steam that escaped from the heating channel 210 may flow into the upper compartment 220U of the inflow chamber 220. Fig. 2B shows a sectional view of an example of the inflow chamber 220 along line B-B in Fig. 2. Inflow chamber 220 may have a rectangular section with a height H and a width W. Height H and width W may be in a ratio of 3:2. For example, the height H may be l5mm and the width W may be lOmm. Inflow chamber 220 may have a length L (refer to Fig. 2) of about 20- 25mm, preferably 23mm. Accordingly, the ratio between the width W and the length L may be about 2: 1-5:2. Inflow chamber 220 may have a circular or square section. Referring to Fig. 2, the instant heater 100 may include the outlet valve 104V at about the outlet 104 of the heater 100.

[0036] Fig. 3 shows a schematic diagram of an example of the instant heater 300. As shown in Fig. 3, the duct 312 may have a U-shaped profile. Duct 312 may include a U-shaped elbow 332 with a first side channel 334 and a second side channel 336 extending from each end of the U-shaped elbow 332. U-shaped elbow 332 may be disposed at about the distal end 314D of the heating strip 314. First side channel 334 may be in fluid communication with the inlet 302 and the second side channel 336 may be in fluid communication with the outlet 304. Heating strip 314 may include a first heating surface 314F and a second heating surface 314S behind the first heating surface 314F such that the first side channel 334 may be thermally connected to the first heating surface 314F and the second side channel 336 may be thermally connected to the second heating surface 314S. By having the duct 312 extend along both sides of the heating strip 314, the heating capacity of the heating channel 310 may be increased. In addition, the housing 306 of the instant heater 300 may remain the same or may be more compact even though the length of the duct 312 is been increased. As shown in Fig. 3, the instant heater 300 may have a slot 316 formed between the first side channel 334 and the second side channel 336. Slot 316 may have an opening 316H adapted to receive the heating strip 314 into the slot 316. Slot 316 may have a depth of about 4.2mm, 4.3mm, or 4.4mm.

[0037] Referring to Fig. 3, the instant heater 300 may include an outflow chamber 340 disposed between and in fluid communication with the heating channel 310 and the outlet 304. As described earlier, the outflow chamber 340 may provide a space to allow steam generated from the second side channel 336 to escape to. Similarly, the inflow chamber 320 may allow steam generated form the first side channel 334 to escape to. Outflow chamber 340 may have a cross-sectional area that is larger than that of the duct 312. As shown in Fig. 3, the outflow chamber 340 may have a height longer than the depth of the duct 312. Outflow chamber 340 may have a circular, square or rectangular cross-section.

[0038] Fig. 4 shows a schematic diagram of an example of the instant heater 400. As shown in Fig. 4, the U-shaped elbow 432 may include a reservoir 450 adapted to contain water from the first side channel 434 and/or the second side channel 436. Reservoir 450 may be adapted to accommodate steam generated from the first side channel 434 and/or the second side channel 436. Further, the reservoir 450 may be adapted to trap impurities from the heating channel 410. A gap 452 may be incorporated between the distal end 414D of the heating strip 414 and the reservoir 450 to prevent the reservoir 450 from being heated by the heating strip 414. Reservoir 450 may have a depth of about 13-15mm, preferably 15mm.

[0039] Heating strip 414 may have a linear profile as shown in Fig. 4. While it is not shown in any one of the figures, the heating strip may have a curved profile. Accordingly, the heating channel and therefore the duct may have a corresponding profile to maintain optimal heat transfer between the heating strip and the duct. Heating strip 414 may not be in fluid communication with the duct 412 and may be adapted to heat the water stream via the duct 412. As shown in Fig. 1A, the heating strip 414 may have a thickness of about 4mm and a width of about 20-25mm, preferably 22.5mm. Heating strip 514 may be made of silicon nitride.

[0040] Fig. 5 A shows an enlarged view of an example of the inflow chamber 520. Inflow chamber 520 may include an inflow opening 522 in fluid communication with the inlet 502 (not shown in Fig. 5 A) and an outflow opening 524 in fluid communication with the heating channel 510. Inflow opening 522 may be misaligned from the outflow opening 524. Referring to Fig. 5B, the water enters the inflow chamber 520 via the inflow opening 522 which is at a level higher than the outflow opening 524. By misaligning the inflow opening 522 and the outflow opening 524, the steam escaping from the heating channel 510 into the inflow chamber 520 may not be obstructed by the water entering the inflow chamber 520 via the inflow opening 522. Inflow chamber 520 may include a waste collector 526 adapted collect any waste that is deposited from the water flowing through the inflow chamber 520. Thereafter, the water exits the inflow chamber 520 via the outflow opening 524 and into the heating channel 510 to be heated by the heating strip 514.

[0041] Referring to Fig. 5 A, a gap 514G may be formed between the heating strip 514 and the duct 512. Heating strip 514 may be spaced from the duct 512. As shown in Fig. 5A, the gap 514G may be formed between the heating strip 514 and the first side channel 534. Heat may be transmitted from the heating strip 514 to the duct 512 through the gap 514G to heat the water through the duct 512. Gap 514G between the heating strip 514 and the duct 512 may be in the range of 0.15-0.3mm, preferably 0.15mm. As the heating strip 514 is separated from the water, the risk of the water contacting the heating strip 514 and hence the electrical supply (not shown in Fig. 5) of the heating strip 514 is greatly reduced. As the heating strip 514 may not be rigidly secured to the heating channel 510, the gap 514G may vary. For example, the heating strip 514 may be temporarily in contact with the duct 512 where there may be no gap, i.e. gap 514G is 0mm and the heating strip 514 may move away from the duct 512 and therefore the gap 514G may be up to 0.3mm wide. Due to the gap 514G, the air filled in the gap 514G between the heating strip 514 and the duct 512 increases the heat resistance around the heating strip 514. Due to the heat insulation around the heating strip 514, the power required to generate the same amount of heat to the duct 512 may be lower than the power required when the heating strip 514 is in contact with the duct 512. Therefore, the power consumption of the instant heater 500 may be in the range of l,l00-l,450W, preferably l,l00-l,300W, which is substantially lower than that of a conventional instant heater, e.g. 3,000W.

[0042] Fig. 5B shows an enlarged view of an example of the outflow chamber 540. Outflow chamber 540 may include an inflow opening 542 in fluid communication with the heating channel 510 and an outflow opening 544 in fluid communication with the outlet 504 (not shown in Fig. 5B). Inflow opening 542 may be misaligned from the outflow opening 544. Referring to Fig. 5B, the water enters the outflow chamber 540 via the inflow opening 542 which is at a level lower than the outflow opening 544. By misaligning the inflow opening 542 and the outflow opening 544, the water from the heating channel 510 may not impact the outflow opening 544 of the outflow chamber 540 directly. After the water enters the outflow chamber 540 via the inflow opening 542, the water exits the outflow chamber 540 via the outflow opening 544 and flows toward the outlet 504 to be discharged from the outlet 504.

[0043] As mentioned above, the gap 514G may be formed between the heating strip 514 and the duct 512. Heating strip 514 may be spaced from the duct 512. As shown in Fig. 5B, the gap 514G may be formed between the heating strip 514 and the second side channel 536. Heat may be transmitted from the heating strip 514 to the duct 512 through the gap 514G to heat the water through the duct 512. Gap 514G between the heating strip 514 and the duct 512 may be in the range of 0.15-0.3mm, preferably 0.15mm. As the heating strip 514 may not be rigidly secured to the heating channel 510, the gap 514G may vary. For example, the heating strip 514 may be temporarily in contact with the duct 512 where there may be no gap, i.e. gap 514G is 0mm and the heating strip 514 may move away from the duct 512 and therefore the gap 514G may be up to 0.3mm wide.

[0044] Fig. 6 shows an enlarged view of an example of the inflow chamber 620. Inflow chamber 620 may include a spout 628 extending from the inflow opening 622 into the inflow chamber 620, such that the spout 628 is adapted to direct the inflow water away from the outflow opening 624. As shown in Fig. 6, the spout 628 may be adapted to direct the inflow water direction (see right arrow) from the inflow opening 622 at angle away from said direction, e.g. downwards (see left arrow). [0045] Fig. 7 shows a schematic view of an example of the instant heater 700. As described in one or more of the various examples above, the instant heater 700 may include the heating channel 710 with the heating strip 714 and the duct 712. Instant heater 700 may have a flow valve 708 adapted to control the flow rate of the water entering the heating channel 710. Before the water enters the heating channel 710, the water may first flow through the inflow chamber 720. As the water flows along the first side channel 734 of the duct 712, the water is being heated by the heating strip 714. At the end of the first side channel 734, the heating channel 710 may include a reservoir 750 where the water enters before entering the second side channel 736. As shown, the reservoir 750 may be disposed at the U-shaped elbow 732 between the first side channel 734 and the second side channel 736. Water may be heated along the second side channel 736 after leaving the reservoir 750. When the water exits the heating channel 710, the water may enter the outflow chamber 740 before exiting the instant heater 700 via the outlet 704.

[0046] When the water entering the instant heater 700 is stopped, e.g. when the tap is turned off, the heating would cease as the electrical supply to the heating strip 714 would be turned off by the controller when the water stoppage is detected. Although the electrical supply is turned off, the heating strip 714 would still be hot and the water retained within the duct 712 will continue to be heated up. Due to the continued heating, the pressure within the duct may increase and steam may be formed. The steam in the first side channel 734 may escape into the inflow chamber 720 and the steam in the second side channel 736 may escape into the outflow chamber 740.

[0047] As shown in Fig. 7, the heating strip 714 may be spaced from the duct 712. Specifically, the gap 714G may be formed between the heating strip 714 and each of the first side channel 734 and the second side channel 736. Similarly, the gap 752 may be formed between the heating strip 714 and the reservoir 750. As shown in Fig. 7, the heating strip 714 may include a head 714H connected thereto at the proximal end 714P of the heating strip 714. Electrical connection to the heating strip 714 may be made at the head 714H. A pocket 713 may be formed between the first side channel 734, the second side channel 736 and the U-shaped elbow 732 such that the heating strip 714 may be inserted into the pocket 713 and may be disposed loosely in the pocket 713, i.e. not secured to the housing 706 of the instant heater 700. An advantage of having the heating strip 714 disposed loosely is that any pressure built up within the pocket 713 during the heating process may escape from the pocket 713.

[0048] Instant heater may require a power consumption in the range of l,l00-l,450W, preferably in the range of l,l00-l,300W. As such, the instant heater consumes less than half the average power consumption of a conventional instant heater, i.e. 3,000W. Further, the tankless instant heater as shown above contains lesser water than the conventional instant water heaters and storage water heaters. As mentioned earlier, the conventional instant heater may contain up to 1 litre of water, and the storage water heater may container about 25-30 litres of water. The tankless instant heater according to the present invention may contain about 100 millilitres of water at any one time during operation.

[0049] A skilled person would appreciate that the features described in one example may not be restricted to that example and may be combined with any one of the other examples.

[0050] The present invention relates to an instant heater generally as herein described, with reference to and/or illustrated in the accompanying drawings.

Claims

Claim

1. An instant heater for heating water, the heater comprising:

an inlet adapted to channel water into the heater;

an outlet adapted to channel water out of the heater;

a heating channel in fluid communication with the inlet and the outlet, wherein the heating channel is adapted to heat the water from the inlet and channelled therethrough and the heated water is channelled from the heating channel out of the heater via the outlet, wherein the heating channel comprises a duct in fluid communication with the inlet and outlet; and a heating strip extending alongside and outside the duct, wherein the heating strip is thermally connected to the duct and is adapted to heat the water flowing therethrough;

a flow valve disposed between the heating channel and the inlet, the flow valve adapted to control the flow of the water into the heating channel.

2. The instant heater of claim 1, wherein the duct has an internal depth of 1.6-2.2mm.

3. The instant heater of claim 1, wherein the duct has an internal depth of 1.5-2mm.

4. The instant heater of claim 1, wherein the duct has an internal depth of 1.6-1.8mm.

5. The instant heater of any one of claims 1 to 4, further comprising an inflow chamber disposed between and in fluid communication with the heating channel and the inlet.

6. The instant heater of claim 5, wherein the inflow chamber comprises an inflow opening in fluid communication with the inlet and an outflow opening in fluid communication with the heating channel, wherein the inflow opening is misaligned from the outflow opening.

7. The instant heater of claim 6, wherein the inflow chamber comprises a spout extending from the inflow opening into the inflow chamber, wherein the spout is adapted to direct the water away from the outflow opening.

8. The instant heater of any one of claims 1 to 7, further comprising an outflow chamber disposed between and in fluid communication with the heating channel and the outlet.

9. The instant heater of any one of claims 1 to 8, wherein the duct has a U-shaped profile, wherein the duct comprises a U-shaped elbow with a first side channel and a second side channel extending from each end of the U-shaped elbow, wherein the first side channel is in fluid communication with the inlet and the second side channel is in fluid communication with the outlet, the heating strip comprises a first heating surface and a second heating surface behind the first heating surface, wherein the first side channel is in thermally connected to the first heating surface and the second side channel is thermally connected to the second heating surface.

10. The instant heater of claim 9, wherein the U-shape elbow comprises a reservoir adapted to contain water from the first side channel and the second side channel.

11. The instant heater of claim 1 to 10, wherein the heating strip is spaced from the duct.

12. The instant heater of any one of claims 1 to 11, wherein the heating strip is made of silicon nitride.