AU2011202376B2 - Warm-air heater - Google Patents

Abstract

WARM-AIR HEATER A target value setting unit (81) sets a target combustion temperature of a gas burner 5 (41) for maintaining a steady combustion in a normal state to be lower than the maximum combustion temperature corresponding to a heating power. A combustion control unit (82) controls a fuel gas supply amount to a gas mixing chamber (44) so that the target combustion temperature is achieved. A fan control unit (83) sets a rotation speed higher than a rotation speed corresponding to the maximum combustion temperature in the 1o steady combustion mode in the normal state as the target rotation speed, and controls the rotation speed of a combustion fan (6) to maintain the target combustion temperature based on the combustion temperature detected by a thermocouple (48). When a change amount obtained by subtracting the current rotation speed of the combustion fan from the target rotation speed thereof becomes equal to or greater than an oxygen-deficient change 15 amount obtained by subtracting a rotation speed corresponding to the target combustion temperature in the oxygen-deficient combustion mode from the target rotation speed, a control unit (8) determines that it is in the oxygen-deficient state, and stops combustion at the gas burner (41).

Description

S&F Ref: 999307 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Rinnai Corporation, of 2-26, Fukuzumi-cho, Nakagawa of Applicant: ku, Nagoya-shi, Aichi-ken, 454-0802, Japan Actual Inventor(s): Hayato Mizouchi Kazunori Nishio Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Warm-air heater The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(4905012_1) 1 WARM-AIR HEATER BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a warm-air heater that has an all primary air combustion type gas burner which mixes a fuel gas and an indoor combustion air to combust. Description of the Related Art A conventional gas warm-air heater includes, inside a body case provided with an air intake port and a blowoff port, a duct communicating with the air intake port and the blowoff port, a combustion chamber having a gas burner, and an air blower fan, the combustion chamber and the air blower fan both being installed in the duct. The gas warm-air heater is configured to: suction an indoor air into the duct from the air intake port by the rotary operation of the air blower fan; introduce the suctioned air partially into the combustion chamber to heat the same; and thereafter, mix the heated air with the suctioned air at the indoor temperature, to blow warm air from the blowoff port indoors, to thereby carry out indoor heating. Further, since the indoor oxygen concentration reduces in accordance with progression of the combustion operation of a combustion appliance used indoors such as a gas warm-air heater, a thermocouple (TC) is disposed to be brought into contact with the burning face of the gas burner, so as to exert control to stop the combustion of the burner when the TC output value reaches a prescribed reference voltage (e.g., Japanese Unexamined Patent Application Publication No. 2000-154918). Meanwhile, in the combustion chamber where high temperatures and pressures are reached, nitrogen is prone to be oxidized, and an amount of generated nitrogen oxide (NOx) increases. It is regarded that, what is effective for suppressing such generation of NOx is to eliminate a local high-temperature region, so that the combustion temperature reduces. That is, in order to achieve a reduction in NOx, the fuel gas and the combustion air should fully be mixed previously such that the combustion air becomes excessive before combustion. In this manner, it becomes possible to minimize variations in the temperature distribution in the combustion chamber. Accordingly, with the gas warm-air heater, by controlling the mixing proportion of the fuel gas and the combustion air in mixing them such that the resultant mixture becomes as lean as possible, it becomes possible to achieve a low and uniform temperature distribution in the combustion chamber, and to achieve a great reduction in generation of NOx.

2 For example, in a case where the heating operation is carried out in a state where the oxygen concentration is in the normal state (oxygen concentration 21%), allowing the fan to rotate at a low speed to reduce the air excess ratio, it becomes possible to increase the proportion of the fuel gas, to carry out the combustion operation where the TC output value being the detected value of the combustion temperature attains the maximum combustion temperature. However, such a combustion operation carried out at the maximum combustion temperature increases NOx. Accordingly, allowing the fan to rotate at a high speed such that the TC output value in the combustion operation mode attains a value lower than the TC output value at the maximum combustion temperature reduces the proportion of the fuel gas, whereby a reduction in NOx can be achieved. However, in the gas warm-air heater that exerts control to reduce NOx in the manner described above, the rotation speed of the fan is controlled to obtain a constant TC output value. Therefore, when the combustion temperature reduces in accordance with a reduction in the oxygen concentration, control is exerted to reduce the rotation speed of the fan such that the TC output value becomes constant, to thereby increase the proportion of the fuel gas. This poses the problem disclosed in Japanese Unexamined Patent Application Publication No. 2000-154918, i.e., becoming incapable of determining the oxygen-deficient state based on the TC output. Object of the Invention It is the object of the present invention to substantially overcome or at least ameliorate one or more of the foregoing disadvantages. Summary of the Invention A warm-air heater according to the present invention includes: a combustion chamber that has an all primary air combustion type gas burner mixing a fuel gas and a combustion air to combust; a combustion fan that forcibly supplies the combustion air to a gas mixing chamber in the combustion chamber, the fuel gas and the combustion air being mixed in the gas mixing chamber; a temperature detector that detects a combustion temperature near the gas burner; and a control unit that controls a supply amount of each of the fuel gas and the combustion air to the gas mixing chamber, wherein the control unit includes: a target value setting unit that sets a target combustion temperature of the gas burner in a steady combustion mode at a normal oxygen concentration to be lower than a maximum 3 combustion temperature of the gas burner corresponding to a heating power that varies depending on the supply amount of the fuel gas; a combustion control unit that controls the supply amount of the fuel gas to the gas mixing chamber so that a set heating power is achieved; and a fan control unit that sets, as a target rotation speed, a rotation speed of the combustion fan corresponding to the target combustion temperature in the steady combustion mode at the normal oxygen concentration and being higher than a rotation speed corresponding to the maximum combustion temperature, the fan control unit controlling the rotation speed of the combustion fan based on the combustion temperature detected by the temperature detector so as to maintain the target combustion temperature, wherein the control unit determines an oxygen-deficient state and stops combustion when a change amount obtained by subtracting a current rotation speed of the combustion fan from the target rotation speed is equal to or greater than an oxygen-deficient change amount obtained by subtracting a rotation speed corresponding to the target combustion temperature in an oxygen deficient combustion mode from the target rotation speed. The warm-air heater according to an embodiment of the present invention is capable of controlling the rotation speed of the combustion fan based on the detected combustion temperature detected by the temperature detector, such that the combustion temperature of the all primary air combustion type gas burner can attain a constant temperature which is lower than the maximum combustion temperature. Therefore, it becomes possible to carry out a heating operation with a small nitrogen oxide emission amount. Furthermore, even when the combustion operation is carried out for the purpose of reducing the nitrogen oxide emission amount based on the sensed result of the thermocouple (TC) such that the target combustion temperature being lower than the maximum combustion temperature is maintained constant, the oxygen-deficient state is determined not based on the TC output value, but instead, it is determined based on the change amount of the rotation speed of the combustion fan. Therefore, the oxygen-deficient combustion can surely be stopped.

4 Further, in the warm-air heater, preferably, the control unit is configured to exert control to determine a recovery from the oxygen-deficient state based on a lapse of a prescribed time from the stop of combustion due to the oxygen-deficient state. Such a warm-air heater is capable of easily determining the recovery from the s oxygen-deficiency, based on a lapse of time from the stop of combustion due to the oxygen-deficiency. Further, the warm-air heater preferably further includes temperature detecting means for detecting an indoor temperature, and the control unit is configured to exert control to determine a recovery from the oxygen-deficient state, based on a prescribed to temperature drop with reference to an indoor temperature at a time point of the stop of combustion due to the oxygen-deficient state. Such a warm-air heater is capable of easily determining the recovery from the oxygen-deficiency, based on the indoor temperature drop state with reference to the indoor temperature at a time point of the stop of combustion due to oxygen-deficiency. 15 Still further, in the warm-air heater described above which determines the recovery from the oxygen-deficient state based on a lapse of prescribed time or based on a prescribed temperature drop from the stop of combustion due to oxygen-deficiency, the fan control unit exerts control to allow the combustion fan to rotate at a rotation speed lower than the target rotation speed to start the steady combustion, and to allow the 20 rotation speed to increase until the combustion temperature drops to the target combustion temperature based on the combustion temperature detected by the temperature detector, and the fan control unit sets an initial target rotation speed being lower than the target rotation speed at the start of the steady combustion, and sets, as a varying target rotation 25 speed varying over time, a rotation speed of the combustion fan increasing from the start of the steady combustion and ranging from the initial target rotation speed to the target rotation speed corresponding to the target combustion temperature, and wherein the control unit makes a determination as to the oxygen-deficient state by calculating an actual rotation speed change amount by subtracting the current rotation 30 speed from the varying target rotation speed having been set for a time point of making such determination as to the oxygen-deficient state, the control unit making the determination as to the oxygen-deficient state, in a case where the steady combustion is started during a period from when combustion is stopped due to the oxygen-deficient state until the recovery from the oxygen-deficient state is made, by calculating the actual 5 rotation speed change amount based on a varying target rotation speed having been set immediately before the stop of combustion. With such a warm-air heater, by setting a varying target rotation speed, the varying target rotation speed varies from a varying target rotation speed which is an initial target rotation speed to a varying target rotation speed which is a target rotation speed corresponding to the target combustion temperature, based on the detected combustion temperature. Accordingly, with the warm-air heater, so long as the steady combustion in the normal oxygen concentration state is carried out, the target rotation speed corresponding to the target combustion temperature is eventually set simply by setting the target combustion temperature. Furthermore, during a period from when combustion is stopped due to oxygen-deficiency and until a recovery from the oxygen-deficient state is made, a determination as to oxygen deficiency is made irrespective of the initial target rotation speed, and instead, it is made by calculating an actual rotation speed change amount based on a varying target rotation speed having been set immediately before combustion was stopped due to oxygen-deficiency. Therefore, even when the steady combustion is started during a period from when combustion was stopped due to the oxygen-deficiency and until when a recovery from the oxygen-deficient state is made, the steady combustion can be carried out in accordance with the varying target rotation speed immediately before combustion was stopped. Therefore, a determination as to the oxygen-deficiency can accurately be made. Further, the warm-air heater is preferably configured such that the control unit sets the oxygen-deficient change amount corresponding to the supply amount of the fuel gas supplied to the gas mixing chamber. Such a warm-air heater can surely determine oxygen-deficiency in accordance with the heating power. As described above, the warm-air heater in an embodiment of the present invention is capable of carrying out the heating operation with a small nitrogen oxide emission amount, and of surely avoiding the oxygen-deficient state. Brief Description of the Drawings Fig. 1 is an overall configuration diagram of a gas fan heater which is a warm-air heater according to an embodiment of the present invention; Fig. 2 is a control block diagram of the gas fan heater according to the embodiment of the present invention 6 Fig. 3 is a graph showing the relationship for each oxygen concentration between the rotation speed of the combustion fan and the output value of a thermocouple when a heating operation is carried out using the gas fan heater according to the embodiment of the present invention with a high heating power; 5 Fig. 4 is an operational flowchart of the gas fan heater according to the embodiment of the present invention; Fig. 5 is an operational flowchart of the gas fan heater according to the embodiment of the present invention; Fig. 6 is an operational flowchart of the gas fan heater according to the embodiment io of the present invention; and Fig. 7 is a graph showing the relationship for each oxygen concentration between the rotation speed of the combustion fan and the output value of the thermocouple when a heating operation is carried out using the gas fan heater according to the embodiment of the present invention with a low heating power. 15 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings, a description will be given below of a gas fan heater which is a warm-air heater implementing an embodiment of the present invention. With reference to Fig. 1, a gas fan heater I according to the present embodiment 20 includes a rectangular body case 11. The body case 11 is provided with a blowoff port 12 at a bottom portion on its front side, and is provided with a first air intake port 13 and a second air intake port 14 being smaller in area than the first air intake port 13 on its back side. The first air intake port 13 and the second air intake port 14 are covered by one air filter 15. The air filter 15 is removably attached to the body case 11, so as to prevent 25 inflow of motes, dust and the like into the body case 11. Disposed inside the body case 11 is a duct 2 in which a gas burner 41 and a convection fan 3 are disposed. Inside the duct 2, a combustion chamber 4 having the gas burner 41 is disposed at an upper portion of the duct 2, and a convection fan 3 is provided below the combustion chamber 4. 30 The duct 2 communicates with the first air intake port 13 and the blowoff port 12, to structure a mixed air-use passage 20 which serves as an air-blow path for warm air. One intake side opening portion 21 on an upstream side of the duct 2 opposes to the first air intake port 13 formed at the body case 11, and the other blowoff side opening portion 22 on a downstream side of the duct 2 opposes to the blowoff port 12 of the body case 11. A 35 movable louver 16 is attached to the blowoff port 12 for adjusting the opening degree 7 thereof. The movable louver 16 is driven by a geared motor 17. The geared motor 17 has its drive operation controlled by a control unit 8. The gas burner 41 includes a mixing tube portion 42, an all primary air combustion type combustion plate 43 in which a multitude of flame holes are formed, and a gas s mixing chamber 44 formed below the combustion plate 43, into which a mixture gas made up of the fuel gas and the combustion air is introduced from the mixing tube portion 42. The combustion chamber 4 includes a gas burner 41, and a combustion cylinder 45 disposed to surround the combustion plate 43. A flow divider plate 46 is disposed so as to oppose to a top opening portion of the combustion cylinder 45. 1o Beside the duct 2, a combustion air passage 5 communicating with the second air intake port 14 is defined. In the combustion air passage 5, the mixing tube portion 42 of the gas burner 41 exposed externally from a sidewall of the duct 2 is disposed. To a base end portion of the mixing tube portion 42, a combustion fan 6 is attached. The combustion fan 6 suctions the air taken inside the combustion air passage 5 from the is second air intake port 14 as the combustion air, and forcibly discharges it into the gas mixing chamber 44 of the combustion chamber 4 through the mixing tube portion 42. Such disposition of the combustion fan 6 makes it possible to accurately control the amount of the combustion air supplied to the gas mixing chamber 44 through control exerted over the rotation of the combustion fan 6, and to mix the combustion air and the 20 fuel gas at the accurate air excess ratio. Accordingly, as will be described later, by monitoring changes in the rotation speed of the combustion fan 6, the oxygen-deficient state can also be determined further accurately. The combustion fan 6 is structured with a sirocco fan having a combustion fan motor 61 whose rotation speed varies proportionally to the amount of passing current, and 25 a rotary vane 62 having a multitude of small forward curved vanes on a cylinder and being driven to rotate by the combustion fan motor 61. The combustion fan 6 is provided with a second rotation speed sensor 63 structured with a Hall element and the like to detect its rotation speed. The second rotation speed sensor 63 outputs a signal corresponding to the rotation speed of the combustion fan motor 61 to the control unit 8. 30 Further, inside the combustion air passage 5, a first solenoid valve 71, a second solenoid valve 72, and a proportional control valve 73 each provided at a gas supply pipe 7, and a control unit 8 are also disposed. The first solenoid valve 71 and the second solenoid valve 72 open when they are energized. When the first solenoid valve 71 and the second solenoid valve 72 are open, they allow the fuel gas to pass toward a nozzle 74 35 provided at a tip of the gas supply pipe 7; when the valves 71 and 72 are de-energized and 8 closed, they shut off the passage of the fuel gas. The proportional control valve 73 is a valve whose opening degree increases proportionally to the amount of passing current, and it adjusts the supply amount of the fuel gas to the gas burner 41. The control unit 8 controls the opening operation of the first solenoid valve 71, the second solenoid valve s 72, and the proportional control valve 73. Further, in the combustion air passage 5, an indoor temperature sensor 91 detecting indoor temperatures is provided near the second air intake port 14 in the body case 11. Inside the mixing tube portion 42 of the gas burner 41, a downstream end of the gas supply pipe 7 for supplying the gas burner 41 with the fuel gas is inserted. The nozzle 74 10 is formed at the tip of the gas supply pipe 7. The fuel gas injected from the nozzle 74 and the combustion air introduced by the combustion fan 6 are mixed, and introduced into the gas mixing chamber 44 of the combustion chamber 4. Further, an ignition electrode 47 for igniting the mixture gas made up of the combustion air and the fuel gas, and a thermocouple (TC) 48 which is a temperature 15 sensor for sensing the temperature of the combustion flame, are disposed above the combustion plate 43 inside the combustion cylinder 45. The thermocouple 48 is disposed near the combustion plate 43. When being exposed to the combustion flame of the gas burner 41, the thermocouple 48 generates a thermoelectromotive force in accordance with the temperature of the combustion flame. The thermoelectromotive force is output to the 20 control unit 8. The indoor air is suctioned into the combustion air passage 5 of the body case 1 1 from the second air intake port 14 by the actuation of the combustion fan 6, to be introduced into the mixing tube portion 42. The combustion air introduced into the mixing tube portion 42 flows, together with the fuel gas, into the gas mixing chamber 44 25 of the gas burner 41. The exhaust gas produced by combustion at the gas burner 41 flows along the flow divider plate 46 from an opening formed at the top of the combustion cylinder 45, and is discharged into the mixed air passage 20 formed in the duct 2. Then, when the indoor air is suctioned from the first air intake port 13 into the duct 2 by the actuation of the convection fan 3 as the mixing air, the mixing air and the exhaust 30 gas produced by the combustion at the gas burner 41 are mixed. The air mixture becomes warm air, and blows out indoors from the blowoff port 12 opposing to the blowoff side opening portion 22 of the duct 2. The convection fan 3 has a convection fan motor 31 whose rotation speed varies proportionally to the amount of passing current, and a rotary vane 32 disposed to face the 35 blowoff port 12 in the mixed air passage 20, and driven to rotate by the convection fan 9 motor 31. The convection fan 3 is provided with a first rotation speed sensor 33 structured with a Hall element and the like to detect its rotation speed. The first rotation speed sensor 33 outputs a signal corresponding to the rotation speed of the convection fan motor 31 to the control unit 8. 5 As schematically shown in Fig. 1, a console 18 having, e.g., an operational switch 92, a temperature set switch 93, and an informing unit 94 structured with a liquid crystal monitor, is provided at the top face portion of the body case 11. The operational switch 92 is turned on and off by the user, to instruct the control unit 8 of start and stop of heating operation control. The temperature set switch 93 which is an indoor temperature io setter is for setting a desired indoor temperature. Through the operation of the temperature set switch 93 by the user, the desired temperature is increased or decreased by 1*C, for example. The set desired temperature is immediately transmitted to the control unit 8. The informing unit 94 displays the information output from the control unit 8. In particular, when an oxygen-deficient state is entered, it displays an error 15 notification indicative of oxygen-deficiency. It is to be noted that, the informing unit 94 is not limited to such a monitor, and may be structured with a lamp or a speaker that notifies an error of oxygen-deficiency and the like. Further, the control unit 8 controls rotation of the convection fan 3, that of the combustion fan 6 and combustion of the gas burner 41, based on signals received from 20 the detectors such as the thermocouple 48, the indoor temperature sensor 91 and the like. Next, with reference to Fig. 2, a description will be given of the structure of the control unit 8. The control unit 8 is structured using a microcomputer or the like, and includes a target value setting unit 81, a combustion control unit 82 and a fan control unit 83. 25 The target value setting unit 81 sets the target combustion temperature (target TC output value) of the gas burner 41 for maintaining the steady combustion in the normal oxygen concentration state (oxygen concentration 21%) to be smaller than the maximum combustion temperature, so as to reduce the nitrogen oxide emission amount. That is, the target combustion temperature (target TC output value) is set to be smaller than the 30 maximum TC output value indicative of the maximum combustion temperature of the gas burner 41 corresponding to its heating power (in the present embodiment, the maximum combustion temperature is TC output value 24 mV for the high heating power, and TC output value 27 mV for the low heating power). In the present embodiment, the target TC output value is set to TC output value 15 mV for the high heating power, and to TC 35 output value 18 mV for the low heating power. Such setting value of the target 10 combustion temperature (target TC output value) may be determined by the user through the console 18, or may previously be determined by the manufacturer of the gas fan heater 1. The combustion control unit 82 determines a target gas combustion amount of the 5 gas burner 41 such that the set temperature and the temperature detected by the indoor temperature sensor 91 substantially agree with each other. The combustion control unit 82 ignites the gas burner 41, extinguishes combustion at the gas burner 41, and adjusts the combustion amount (i.e., adjusts the fuel gas supply amount), by controlling energization of the first solenoid valve 71, the second solenoid valve 72, and the proportional control io valve 73 provided at the gas supply pipe 7, and the ignition electrode 47, such that the gas burner 41 produces combustion by the target gas combustion amount. Control over the fuel gas supply amount to the gas mixing chamber 44 is exerted based on adjustment of the opening degree of the proportional control valve 73, which is carried out in accordance with the heating power or warming air conditioning operation that the user is desires. Further, the combustion control unit 82 exerts warming air conditioning control also, so as to, when the detected temperature of the indoor temperature sensor 91 rises to reach a prescribed operation halting temperature, set the target gas combustion amount of the gas burner 41 to zero, to stop the combustion operation of the gas burner 41; and 20 thereafter, when the detected temperature of the indoor temperature sensor 91 drops to be equal to or lower than a prescribed operation resuming temperature, to resume the combustion operation of the gas burner 41. Further, when the indoor environment enters an oxygen-deficient state (oxygen concentration 17%) by the combustion operation, the combustion control unit 82 also exerts control to stop the combustion operation of the gas 25 burner 41, by closing the first solenoid valve 71, the second solenoid valve 72, and the proportional control valve 73. Based on the TC output value detected by the thermocouple 48, the fan control unit 83 controls the rotation speed of the combustion fan 6 so as to maintain the target TC output value, which is the target combustion temperature. 30 That is, in order to allow the gas burner 41 to produce combustion at the target combustion temperature described above, the fan control unit 83 sets the rotation speed of the combustion fan 6 in mixing the fuel gas and the combustion air in the gas mixing chamber 44, so as to reduce the proportion of the fuel gas and attain the excess air state. Specifically, the target rotation speed at which the combustion fan 6 eventually stabilizes, 35 which corresponds to the target TC output value in the steady combustion mode in the 11 normal state where the oxygen concentration is 21%, is set to be higher than the rotation speed (in the present embodiment, 2800 rpm for the high heating power, and 1000 rpm for the low heating power) corresponding to the maximum combustion temperature. In the present embodiment, the stable target rotation speed of the combustion fan 6 in the 5 steady combustion mode in the normal state is set to 4800 rpm which corresponds to the target TC output value 15 mV for the high heating power, and is set to 1400 rpm which corresponds to the target TC output value 18 mV for the low heating power. Such setting of the target rotation speed will be detailed later. It is to be noted that, the target rotation speed of the combustion fan 6 1o corresponding to the target combustion temperature in the steady combustion mode in the normal state may be set such that the air excess ratio of equal to or greater than 1.5 and equal to or smaller than 2.0 is obtained. For example, the rotation speed of the combustion fan 6 may be set to fall within the range of 4500 to 6000 rpm for the high heating power. Setting the air excess ratio in such a manner, the heating operation with is suppressed nitrogen oxide generation can be achieved. Further, in order to control the supply amount of the combustion air to the gas burner 41 and the supply amount of the mixing air introduced from the first air intake port in accordance with the heating power being set by the combustion control unit 82, the fan control unit 83 adjusts the current amount supplied to the convection fan motor 31 and the 20 combustion fan motor 61. Specifically, in order to achieve the heating operation with the set heating power, the rotation speed of the convection fan motor 31 and that of the combustion fan motor 61 are detected by the first rotation speed sensor 33 and the second rotation speed sensor 63, to adjust the current supply amount to the fan motors 31 and 61. The rotation speed storage unit 84 is provided at the fan control unit 83, to store the 25 in-operation rotation speed of the convection fan motor 31 of the convection fan 3 and that of the combustion fan motor 61 of the combustion fan 6 in a time-oriented manner. The rotation speed of the convection fan motor 31 and that of the combustion fan motor 61 are obtained based on the rotation speed detected by the first rotation speed sensor 33 and the second rotation speed sensor 63. Further, in the present embodiment, as will be 30 described later, control is exerted such that the target rotation speed (varying target rotation speed) varies. The rotation speed storage unit 84 previously stores therein an initial target rotation speed (Ra: 3000 rpm for the high heating power, and Rf: 850 rpm for the low heating power), the description of which will be given later, and stores the varying target rotation speed every time it varies.

12 Further, when the TC output value reduces due to a reduction in the oxygen concentration, the fan control unit 83 reduces the rotation speed of the combustion fan 6 such that the target TC output value is attained. When the oxygen concentration further reduces to enter the oxygen-deficient combustion (oxygen concentration 17%), and the 5 change amount from the varying target rotation speed set for that time point to the current rotation speed becomes equal to or greater than a prescribed oxygen-deficient change amount, the fan control unit 83 outputs a combustion stop signal to the combustion control unit 82, and stops the combustion fan 6. Next, with reference to Figs. 3 and 7 each being a graph showing the relationship 1o for each oxygen concentration between the rotation speed of the combustion fan and the output value of the thermocouple, and the flowcharts of Figs. 4 to Fig. 6, a description will be given of the oxygen-deficiency determination control operation of a warm-air heater by the control unit 8. When the user turns on the operational switch 92 for starting the heating operation is (step SI 1), the combustion control unit 82 opens the first solenoid valve 71 and the second solenoid valve 72, and opens the proportional control valve 73 by its maximum opening degree. The fan control unit 83 rotates the convection fan motor 31 and the combustion fan motor 61 to drive the convection fan 3 and the combustion fan 6 (step S 12). At this time, the combustion fan 6 is rotated at the igniting rotation speed 2800 20 rpm. Then, the ignition electrode 47 is energized, to thereby ignite the gas burner 41 (step S13). When the gas burner 41 is ignited, whether or not the current TC output value is equal to or greater than 5 mV is determined based on the detection result of the thermocouple 48 (step S 14). When the TC output value is equal to or greater than 5 mV, 25 (Yes in step S14), energization of the ignition electrode 47 is stopped based on the gas burner 41 being ignited, and the combustion fan 6 is rotated at the initial combustion operation rotation speed 3600 rpm, to start the initial combustion operation (step S 15). When the initial combustion operation is started, whether or not the TC output value becomes equal to or greater than 16 mV is determined (step S 16). When the TC output 30 value is equal to or greater than 16 mV, with the proportional control valve 73 opened widely, the combustion fan 6 is caused to rotate at 3800 rpm, which is lower than the varying target rotation speed 4800 rpm corresponding to the target combustion temperature in the normal oxygen concentration state. At the same time, the timer starts counting from zero seconds, to start the steady combustion operation of maintaining the 13 TC output value constant in the combustion operation with the high heating power (step Si7). When the steady combustion operation with the high heating power is started, first, whether or not a current TC output value exceeds the target TC output value (in the 5 present embodiment, 15 mV) is determined (step S18). When the current TC output value exceeds the target TC output value (Yes in step SI 8), in order to reduce a current TC output value to the target TC output value, x rpm (in the present embodiment, 1 rpm) is added to the current rotation speed of the combustion fan 6, to increase the rotation speed of the combustion fan 6 (step S 19). The increased rotation speed is stored in the io rotation speed storage unit 84 of the control unit 8. When the rotation speed of the combustion fan 6 is changed, whether or not such changed rotation speed of the combustion fan 6 exceeds the varying target rotation speed stored in the rotation speed storage unit 84 is determined (step S20). The varying target rotation speed at the start of the steady combustion operation with the high heating power 15 is set to the initial target rotation speed (Ra: 3000 rpm). However, the varying target rotation speed is changed until a stable TC output value with reference to the target TC output value is obtained, and is kept to be stored in the rotation speed storage unit 84. Accordingly, when the changed rotation speed is equal to or smaller than the varying target rotation speed set for that time point, that varying target rotation speed is 20 maintained (step S21); when the changed rotation speed is greater than the varying target rotation speed set for that time point (Yes in step S20), whether or not t minutes (in the present embodiment, two minutes) have elapsed since the timer has started counting the steady combustion operation is determined (step S22). Then, when t minutes have not been elapsed, the varying target rotation speed until then is maintained (step S21). When 25 t minutes have elapsed, the varying target rotation speed is changed to the rotation speed which has been changed in step S19, and the changed varying target rotation speed is stored in the rotation speed storage unit 84 (step S23). As represented by the solid line shown in Fig. 3, in the present embodiment, the rotation speed (Rb: 3800 rpm) of the combustion fan 6 when the steady combustion 30 operation is started is higher than the initial target rotation speed (Ra: 3000 rpm), and furthermore, the TC output value (Vb: 20 mV) at this time is higher than the target TC output value (Vc: 15 mV) (Yes in step S 18). Then, when the TC output value greater than the target TC output value (15 mV) continues until a lapse of t minutes while the rotation speed continues to increase by 1 rpm from 3800 rpm, in step S23, the varying 35 target rotation speed is changed to a changed rotation speed which is higher than 3800 14 rpm. Then, until the TC output value eventually stabilizes to fall within a range of± 0.5 mV with reference to the target TC output value (Vc) 15 mV, the control of increasing the rotation speed of the combustion fan 6 is exerted. In the present embodiment, the rotation speed is eventually stabilized at approximately 4800 rpm (Rc). 5 Further, when the current TC output value is equal to or smaller than the target TC output value in step S18; when the varying target rotation speed is maintained in step S21; or when the varying target rotation speed is changed to the changed rotation speed in step S23, subsequently, whether or not the current TC output value is smaller than the target TC output value is determined (step S24). 10 When the current TC output value is equal to or greater than the target TC output value (No in step S24), and any change in the heating power or stopping the appliance is not necessary, the control returns to step S18 through steps S34 and S35 whose description will be given later, to continue the steady combustion operation with the high heating power. When the oxygen concentration is in the normal state, the TC output is value (Vb) at the time point where the steady combustion operation is started is higher than the target TC output value (Vc). Therefore, the rotation speed of the combustion fan 6 is increased. Then, until the TC output value detected by the thermocouple 48 reaches the target TC output value (Vc), the control returns in step S24 to step S18. In this manner, without carrying out the combustion operation with the TC output value 20 indicative of the maximum combustion temperature, but instead, by allowing the combustion fan 6 to rotate at a high speed such that the TC output value becomes smaller than the TC output value indicative of the maximum combustion temperature, so as to attain the state where the proportion of the combustion air in the gas mixing chamber 44 is increased, a reduction in the nitrogen oxide emission amount can be attained. 25 Then, when the current TC output value becomes smaller than the target TC output value in the steady combustion operation mode (Yes in step S24), in order to increase the TC output value such that the target TC output value (Vc) is attained, the current rotation speed of the combustion fan 6 is reduced by x rpm (1 rpm) (step S25), so that the rotation speed of the combustion fan 6 eventually stabilizes approximately at 4800 rpm (Rc). This 30 makes it possible to increase the proportion of the fuel gas such that the combustion temperature increases, whereby the TC output value is maintained constant. It is to be noted that, also in a case where the rotation speed of the combustion fan 6 is eventually stabilized in the steady combustion operation mode, and thereafter the indoor oxygen concentration drops and whereby the combustion temperature drops, the control of 15 reducing the current rotation speed of the combustion fan 6 is similarly exerted, so as to increase the TC output value to attain the target TC output value (Vc). In step S25, when the rotation speed of the combustion fan 6 is changed to be reduced by x rpm, the changed rotation speed is stored in the rotation speed storage unit 5 84 of the control unit 8. Next, based on the data of the rotation speed stored in the rotation speed storage unit 84, a determination is made as to whether or not the change amount from the varying target rotation speed of the combustion fan 6 set for that time point to the changed rotation speed of the combustion fan 6 exceeds a prescribed oxygen deficient change amount (1200 rpm) which is a reduction amount in the rotation speed 10 from the eventually stabilized varying target rotation speed of the combustion fan 6 (in the present embodiment, 4800 rpm) to the rotation speed (3600 rpm) of the combustion fan 6 where the TC output value in a case where the combustion operation is carried out in the oxygen-deficient state (oxygen concentration 17%) attains the target TC output value (15 mV) (step S26). It is to be noted that, the rotation speed storage unit 84 also is stores therein the rotation speed (Re: 3600 rpm) of the combustion fan 6 at which the TC output value attains the target TC output value (15 mV) when the combustion operation is carried out in the oxygen-deficient state (oxygen concentration 17%) represented by the fine broken line shown in Fig. 3. Since the combustion temperature sensed by the thermocouple 48 reduces in 20 accordance with a reduction in the oxygen concentration, in order for the TC output value to attain the target TC output value, it is necessary to reduce the proportion of the combustion air in the gas mixing chamber 44, and to increase the proportion of the fuel gas. Accordingly, as shown in Fig. 3, the rotation speed of the combustion fan 6 reduces Rc - Rd - Re, such that the TC output value achieves the target TC output value (15 25 mV) at xl on the solid line in the steady combustion state in the normal oxygen concentration state (oxygen concentration 21%); at yI on the broad broken line representing the combustion in the reduced oxygen concentration; and at zl on the fine broken line representing an oxygen-deficient combustion state. As a result, the difference between the rotation speed of the combustion fan 6 and the eventually stabilized varying 30 target rotation speed (4800 rpm) of the combustion fan 6 in the steady combustion state in the normal oxygen concentration state gradually increases. Accordingly, when the change amount of the rotation speed of the combustion fan 6 becomes equal to or greater than the oxygen-deficient change amount (Yes in step S26), it is determined that the indoor environment is in the oxygen-deficient state. When it is 35 determined that the indoor environment is in the oxygen-deficient state, as shown in Fig.

16 5, the combustion control unit 82 closes the first solenoid valve 71, the second solenoid valve 72 and the proportional control valve 73, and the fan control unit 83 stops the convection fan motor 31 and the combustion fan motor 61 to stop the convection fan 3 and the combustion fan 6. Thus, combustion at the gas burner 41 is stopped (step S27). 5 When the combustion is stopped in step S27, a determination is made as to whether or not the appliance has stopped based on the determination of the oxygen-deficiency (step S28). When the appliance has stopped based on the oxygen-deficiency (Yes in step S28), the informing unit 94 informs of the indoor oxygen-deficient state (step S29). Further, when the appliance has stopped because of the operational switch having been 10 turned off (No in step S28), the informing unit 94 does not give any information. Then, until a lapse of 30 minutes from the stop of combustion, the control over the heating operation continues (No in S30), and the eventually stabilized varying target rotation speed having been set immediately before the stop of combustion (4800 rpm for the high heating power, and 1400 rpm in a case where the low heating power operation, whose is description will be given later, is carried out) is maintained (step S31). When the operational switch 92 is turned on before a lapse of 30 minutes (Yes in step S32), the control returns to step S12 in Fig. 4, and the gas burner 41 is ignited. When the steady combustion operation is entered, the control is exerted to determine as to an increase or a reduction in the rotation speed of the combustion fan 6 under the condition 20 where the varying target rotation speed is maintained at 4800 rpm for the high heating power, and at 1400 rpm in a case where the low heating power is carried out. When the operational switch 92 has not been turned on until a lapse of 30 minutes from the stop of combustion (Yes in step S30), the varying target rotation speed stored in the rotation speed storage unit 84 is reset to 3000 rpm for the high heating power, and 25 reset to 850 rpm for the low heating power (step S33). Thus, the heating operation ends. On the other hand, when the change amount of the rotation speed of the combustion fan 6 is less than a prescribed oxygen-deficient change amount in step S26 (No in step S26), a determination is made as to whether or not changeover from the high heating power to the low heating power has been carried out so that the heating power becomes 30 low, by the user switching the operation or by the warming air conditioning operation based on the indoor temperature sensor 91 (step S34). When the heating power has not been changed over (No in step S34), whether or not the operational switch 92 has been turned off is determined (step S35). When the operational switch 92 has not been turned off (No in step S35), the control returns to step S 18, and the steady combustion operation 35 with the high heating power continues. When the operational switch 92 has been turned 17 off (Yes in step S35), the control of stopping combustion, which appears in steps S27 to S33 in Fig. 5, is exerted. When the heating power has been changed over to be low in step S34 (Yes in step S34), as shown in Fig. 6, with the proportional control valve 73 opened small, the s combustion fan 6 is caused to rotate at 1000 rpm, which is lower than the varying target rotation speed 1400 rpm corresponding to the target combustion temperature in the normal oxygen concentration state. At the same time, the timer starts counting from zero seconds, to start the steady combustion operation of maintaining the TC output value constant in the combustion operation with the low heating power (step S41). 10 When the steady combustion operation with the low heating power is started, the fuel gas supply amount becomes small. Furthermore, the combustion fan 6 rotates at 1000 rpm at which an air excess ratio of approximately 0.9 with the low heating power is attained. Accordingly, the flame formed on the combustion plate 43 becomes small. With the gas burner 41 according to the present embodiment in which the thermocouple 15 48 is provided in close proximity to the combustion plate 43, as represented by the solid line in Fig. 7, when the steady combustion operation is carried out at the oxygen concentration 21 %, the TC output value immediately becomes equal to or greater than 25 mV. In the steady combustion operation with the low heating power, the control similar 20 to that in the steady combustion operation with the high heating power is exerted. First, whether or not the current TC output value exceeds the target TC output value (in the present embodiment, 18 mV) is determined (step S42). When the current TC output value exceeds the target TC output value (Yes in step S42), in order to reduce the current TC output value to the target TC output value, x rpm (in the present embodiment, 1 rpm) 25 is added to the current rotation speed of the combustion fan 6, such that the rotation speed of the combustion fan 6 increases (step S43). The increased rotation speed is stored in the rotation speed storage unit 84 of the control unit 8. When the rotation speed of the combustion fan 6 is changed, whether or not the changed rotation speed of the combustion fan 6 exceeds the varying target rotation speed 30 stored in the rotation speed storage unit 84 is determined (step S44). The varying target rotation speed at the start of the steady combustion operation with the low heating power is set to the initial target rotation speed (Rf: 850 rpm). However, the varying target rotation speed is changed until a stable TC output value with reference to the target TC output value is obtained, and is kept to be stored in the rotation speed storage unit 84. 35 Accordingly, when the changed rotation speed is equal to or smaller than the varying 18 target rotation speed set for that time point, that the varying target rotation speed is maintained (step S45); when the changed rotation speed is greater than the varying target rotation speed set for that time point (Yes in step S44), whether or not t minutes (in the present embodiment, two minutes) have elapsed since the timer has started counting the 5 steady combustion operation is determined (step S46). When t minutes have not been elapsed, the varying target rotation speed until then is maintained (step S45). When t minutes have elapsed, the varying target rotation speed is changed to the rotation speed which has been changed in step S43, and the changed varying target rotation speed is stored in the rotation speed storage unit 84 (step S47). 10 As represented by the solid line shown in Fig. 7, in the present embodiment, the rotation speed (Rg: 1000 rpm) of the combustion fan 6 when the steady combustion operation with the low heating power is started is higher than the initial target rotation speed (Rf: 850 rpm), and furthermore, the TC output value (Vg: 27 mV) at this time is higher than the target TC output value (Vh: 18 mV) (Yes in step S42). Therefore, when is the fan rotation speed continues until a lapse of t minutes while increasing its rotation speed by 1 rpm from 1000 rpm, in step S47, the varying target rotation speed is changed to a changed rotation speed which is higher than 1000 rpm. Then, until the TC output value is stabilized to fall within a range of± 0.5 mV with reference to the target TC output value (Vh) 18 mV, the control of increasing the rotation speed of the combustion 20 fan 6 is exerted. In the present embodiment, the rotation speed is eventually stabilized at 1400 rpm (Rh). Further, when the current TC output value is equal to or smaller than the target TC output value in step S42; when the varying target rotation speed until then is maintained in step S45; or when the varying target rotation speed is changed to the changed rotation 25 speed in step S47, subsequently, whether or not the current TC output value is smaller than the target TC output value is determined (step S48). When the current TC output value is equal to or greater than the target TC output value (No in step S48), and any change in the heating power or stopping the appliance is not necessary, the control returns to step S42 through steps S51 and S52 whose 30 description will be given later, to continue the steady combustion operation with the low heating power. When the oxygen concentration is normal, the TC output value (Vg) at the time point where the steady combustion operation with the low heating power is started is higher than the target TC output value (Vh). Therefore, the rotation speed of the combustion fan 6 is increased. Until the TC output value detected by the thermocouple 19 48 reaches the target TC output value (Vh), the control returns to step S42 in step S48. Thus, a reduction in NOx can be achieved. Then, when the current TC output value becomes smaller than the target TC output value in the steady combustion operation mode (Yes in step S48), in order to increase the s TC output value such that the target TC output value (Vh) is attained, the current rotation speed of the combustion fan 6 is reduced by x rpm (1 rpm) (step S49), so that the rotation speed of the combustion fan 6 eventually stabilizes approximately at 1400 rpm (Rc). In this manner, the TC output value is maintained constant. It is to be noted that, in the steady combustion operation mode with the low heating power also, in the case where the io rotation speed of the combustion fan 6 is eventually stabilized, and thereafter the indoor oxygen concentration drops and whereby the combustion temperature drops, the control of reducing the current rotation speed of the combustion fan 6 is similarly exerted, so as to increase the TC output value to attain the target TC output value (Vh). In step S49, when the rotation speed of the combustion fan 6 is changed to be 15 reduced by x rpm, the changed rotation speed is stored in the rotation speed storage unit 84 of the control unit 8. Next, based on the data of the rotation speed stored in the rotation speed storage unit 84, a determination is made as to whether or not the change amount from the varying target rotation speed of the combustion fan 6 set for that time point to the changed rotation speed of the combustion fan 6 exceeds a prescribed oxygen 20 deficient change amount (300 rpm) which is a reduction amount in the rotation speed from the eventually stabilized varying target rotation speed (in the present embodiment, 1400 rpm) of the combustion fan 6 to the rotation speed (1100 rpm) of the combustion fan 6 where the TC output value in a case where the combustion operation is carried out in the oxygen-deficient state (oxygen concentration 17%) attains the target TC output value 25 (18 mV) (step S50). It is to be noted that, the rotation speed storage unit 84 also stores therein the rotation speed (Rj: 1100 rpm) of the combustion fan 6 at which the TC output value attains the target TC output value (18 mV) when the combustion operation is carried out in the oxygen-deficient state (oxygen concentration 17%) represented by the fine broken line shown in Fig. 7. 30 Accordingly, as shown in Fig. 7, the rotation speed of the combustion fan 6 reduces Rh - Ri -+ Rj, such that the TC output value achieves the target TC output value (18 mV) at x2 on the solid line in the steady combustion state in the normal oxygen concentration state (oxygen concentration 21%); at y2 on the broad broken line representing the combustion state where the oxygen concentration is reduced; and at z2 35 on the fine broken line representing the oxygen-deficient combustion state. Accordingly, 20 the difference between the rotation speed of the combustion fan 6 and the eventually stabilized varying target rotation speed of the combustion fan 6 (1400 rpm) in the steady combustion state in the normal oxygen concentration state gradually increases. Accordingly, when the change amount of the rotation speed of the combustion fan 6 5 becomes equal to or greater than the oxygen-deficient change amount (Yes in step S50), similarly to the combustion operation with the high heating power, as shown in Fig. 5, it is determined that the indoor environment is in the oxygen-deficient state. When it is determined that the indoor environment is in the oxygen-deficient state, the combustion control unit 82 closes the first solenoid valve 71, the second solenoid valve 72 and the 1o proportional control valve 73, and the fan control unit 83 stops the convection fan motor 31 and the combustion fan motor 61 to stop the convection fan 3 and the combustion fan 6. Thus, the combustion at the gas burner 41 is stopped (step S27). Then, the control of stopping combustion, which appears in steps S28 to S33 in Fig. 5, is exerted. On the other hand, when the change amount of the rotation speed of the combustion is fan 6 is less than a prescribed oxygen-deficient change amount in step S50 (No in step S50), a determination is made as to whether or not changeover to the high heating power has been carried out by the user switching the operation or by the warming air conditioning operation based on the indoor temperature sensor 91 (step S51). When the heating power has not been changed over (No in step S5 1), whether or not the operational 20 switch 92 has been turned off is determined (step S52). When the operational switch 92 is not turned off (No in step S52), the control returns to step S42, and the steady combustion operation with the low heating power continues. When the operational switch 92 has been turned off (Yes in step S52), the control of stopping combustion, which appears in steps S27 to S33 in Fig. 5, is exerted. 25 In the present embodiment, since control is exerted such that the varying target rotation speed varies from the initial target rotation speed to the rotation speed corresponding to the target combustion temperature, so long as the steady combustion in the normal oxygen concentration state is carried out, the target rotation speed corresponding to the target combustion temperature is eventually set simply by setting the 30 target combustion temperature. Further, since the varying target rotation speed is controlled to vary from the initial target rotation speed, in the present embodiment, during a period from when the combustion fan 6 is stopped due to the oxygen-deficiency and the fuel gas supply is stopped, and until a lapse of 30 minutes for the recovery from the oxygen-deficient state, 35 the varying target rotation speed is maintained at the varying target rotation speed in the 21 stable mode having been set immediately before combustion was stopped due to oxygen deficiency. Accordingly, during a period from when combustion was stopped due to oxygen-deficiency and until when a recovery from the oxygen-deficient state is made, it is possible to carry out the steady combustion in accordance with the eventually stabilized 5 varying target rotation speed immediately before combustion was stopped. Therefore, even combustion is resumed before the recovery from the oxygen-deficient state is made, oxygen-deficiency can accurately be determined. It is to be noted that, in the present embodiment, control is exerted such that the rotation speed of the combustion fan 6 is increased or decreased by 1 rpm, the manner of 1o increasing or decreasing the rotation speed is not limited thereto. Further, instead of varying the target rotation speed, it may be fixed to, for example, 4800 rpm for achieving the target TC output value (15 mV) for the high heating power; and to 1400 rpm for achieving the target TC output value (18 mV) for the low heating power. Further, the heating power may be controlled not only based on two levels, but also based on three or is more levels. Further, in the present embodiment, the combustion fan 6 is also stopped when the oxygen-deficient state is determined. However, it is also possible for the combustion control unit 82 to just close the first solenoid valve 71, the second solenoid valve 72 and the proportional control valve 73 so as to stop the gas burner 41, and to allow the combustion fan 6 to continuously rotate. 20 Further, in the present embodiment, the recovery from oxygen-deficiency is determined based on a lapse of time. However, the present embodiment may be configured such that the control unit 8 determines the recovery from the oxygen-deficient state based on a prescribed temperature drop from the indoor temperature when combustion is stopped due to the oxygen-deficient state. 25 The present invention is not limited to the embodiment described above, and may be practiced in various modes. For example, the convection fan may be provided near the first air intake port 1 between the first air intake port I and the combustion chamber 4 in the duct 2.

Claims (6)

1. A warm-air heater, comprising: a combustion chamber that has an all primary air combustion type gas burner s mixing a fuel gas and a combustion air to combust; a combustion fan that forcibly supplies the combustion air to a gas mixing chamber in the combustion chamber, the fuel gas and the combustion air being mixed in the gas mixing chamber; a temperature detector that detects a combustion temperature near the gas burner; 10 and a control unit that controls a supply amount of each of the fuel gas and the combustion air to the gas mixing chamber, wherein the control unit includes: a target value setting unit that sets a target combustion temperature of the gas burner 15 in a steady combustion mode at a normal oxygen concentration to be lower than a maximum combustion temperature of the gas burner corresponding to a heating power that varies depending on the supply amount of the fuel gas; a combustion control unit that controls the supply amount of the fuel gas to the gas mixing chamber so that a set heating power is achieved; and 20 a fan control unit that sets, as a target rotation speed, a rotation speed of the combustion fan corresponding to the target combustion temperature in the steady combustion mode at the normal oxygen concentration and being higher than a rotation speed corresponding to the maximum combustion temperature, the fan control unit controlling the rotation speed of the combustion fan based on the combustion temperature 25 detected by the temperature detector so as to maintain the target combustion temperature, wherein the control unit determines an oxygen-deficient state and stops combustion when a change amount obtained by subtracting a current rotation speed of the combustion fan from the target rotation speed is equal to or greater than an oxygen-deficient change 30 amount obtained by subtracting a rotation speed corresponding to the target combustion temperature in an oxygen-deficient combustion mode from the target rotation speed.

2. The warm-air heater according to claim 1, wherein 23 the control unit is configured to exert control to determine a recovery from the oxygen-deficient state based on a lapse of a prescribed time from the stop of combustion due to the oxygen-deficient state. 5

3. The warm-air heater according to claim 1, further comprising temperature detecting means for detecting an indoor temperature, wherein the control unit is configured to exert control to determine a recovery from the oxygen-deficient state based on a prescribed temperature drop with reference to an indoor temperature at a time point of the stop of combustion due to the oxygen-deficient state. 10

4. The warm-air heater according to one of claims 2 and 3, wherein the fan control unit exerts control to allow the combustion fan to rotate at a rotation speed lower than the target rotation speed to start the steady combustion, and to allow the rotation speed to increase until the combustion temperature drops to the target combustion is temperature based on the combustion temperature detected by the temperature detector, and the fan control unit sets an initial target rotation speed being lower than the target rotation speed at the start of the steady combustion, and sets, as a varying target rotation speed varying over time, a rotation speed of the combustion fan increasing from the start 20 of the steady combustion and ranging from the initial target rotation speed to the target rotation speed corresponding to the target combustion temperature, and wherein the control unit makes a determination as to the oxygen-deficient state by calculating an actual rotation speed change amount by subtracting the current rotation speed from the varying target rotation speed having been set for a time point of making 25 such determination as to the oxygen-deficient state, the control unit making the determination as to the oxygen-deficient state, in a case where the steady combustion is started during a period from when combustion is stopped due to the oxygen-deficient state until the recovery from the oxygen-deficient state is made, by calculating the actual rotation speed change amount based on a varying target rotation speed having been set 30 immediately before the stop of combustion.

5. The warm-air heater according to one of claims 1 to 4, wherein the control unit is configured to set the oxygen-deficient change amount corresponding to the supply amount of the fuel gas supplied to the gas mixing chamber. 35 24

6. A warm-air heater substantially as hereinbefore described with reference to the accompanying drawings. Dated 19 May, 2011 s Rinnai Corporation Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON