Field of the invention

The present invention relates to monitoring and improving combustion in wood- burning stoves. Background of the invention

Modern wood-burning stoves arranged in e.g. living rooms or other rooms of a building are used for providing heat, mainly to the respective room in which it is arranged, but also in some degree to other rooms of the building. The wood-burning stoves, especially wood burning stoves of the convection type, provides a type of heat that is appreciated by users, and the wood-burning stoves may also provide a cost efficient alternative to other types of heat sources for heating the room of a building. However, present wood-burning stoves also suffer from some problems. For example, the outdoor environment may be negatively affected by the combustion in the combustion chamber of a wood-burning stove. Another example may be that especially un-experienced users may unintentionally set up for a non-optimal combustion.

It may thus be an object of the present invention to solve the above problems. It may moreover be an object of the invention to provide a solution that may motivate and/or facilitate owners of existing wood-burning stoves to solve the above problems. Summary of the invention

The invention relates to a method of providing combustion-related information related to a combustion of solid fuel, such as wood, in a wood-burning stove (1), the wood-burning stove comprising a combustion chamber (11) defined by an inner stove (12), the inner stove having an outside (121), the wood-burning stove further comprising a combustion monitoring system (2), the combustion monitoring system comprising

a temperature sensor (22) arranged substantially at said outside (121) of the inner stove (12), and

a processing and communication arrangement (21) being coupled to said temperature sensor (22) and further providing a communicative coupling (23) for enabling connection to an output device (24), wherein the temperature sensor, during combustion of said solid fuel, provides a temperature sensor output, and wherein the processing and communication arrangement accepts a connection from the output device and transmits temperature representations relating to the combustion of solid fuel inside said combustion chamber, the temperature representations being derived from the temperature sensor output, and wherein the output device processes said temperature representations to provide an output based on said temperature representations.

An advantageous way of, non-invasively with respect to the combustion chamber, establishing relevant and helpful information about a combustion taking place inside a combustion chamber of a wood-burning stove is hereby provided. The advantages of the present invention makes it beneficial for retrofitting to existing wood-burning stoves, contrary to other combustion monitoring solutions that requires installation inside or penetration into the combustion chamber. The advantageous invention is also incredible helpful for average stove users who like the cosy heating, but are not able to optimize the burning to improve their inside and outside environment and reduce the amount of effort and wood supplies. By the present invention such users can easily monitor the combustion and act when told or suggested to by the method. With the present massive presence of smartphones and tablet computers, most of them Bluetooth enabled, the present invention is relatively inexpensive compared to other more automated solutions, and available to practically everyone.

By not requiring a temperature sensor inside the combustion chamber, the present invention features several advantages over systems with an internal temperature sensor. For example a cheaper temperature sensor may be used with the invention as it only has to withstand and monitor considerably lower temperatures and is not exposed to soot and flue gas. These improved circumstances also mean that an outside temperature sensor according to the invention typically lasts longer and does not need maintenance, e.g. cleaning of soot.

The processing of the temperature representations in an advantageous embodiment comprises analysing the development of temperature with time, e.g. by means of a time-temperature curve. The advantageous invention enables for example an embodiment where the processing comprises predicting the development of the combustion so as to for example estimate and present an optimal time for refuelling, provide advice and tips with regards to for example opening or closing air regulators, etc., or processing different models related to different settings of air regulators or the like so as to estimate optimal refuelling times or heating efficiency for different settings. The present invention enables the establishment of a continuously self-adjusting combustion prognosis for a specific scenario, possibly based on certain user- adjustable parameters such as desired heating power, desired time for next refuelling, desired amount of wood for next refuelling, etc. In other words, the present invention makes it possible to plan a wood stove combustion, besides only monitoring it, and thereby helps the user to obtain a clean, efficient, optimal combustion.

In an advantageous embodiment said temperature sensor is attached to said outside of the inner stove, preferably to an upper part or upper rear part of said outside, even more preferably adjacent to an exhaust opening (18) of said inner stove.

In an advantageous embodiment the combustion monitoring system further comprises a start switch (25) electrically coupled to a circuit of the processing and communicating arrangement, and wherein the processing and communicating arrangement starts a temperature measuring session based on an event related to the start switch, the start switch preferably being mechanically coupled to a primary air damper (14) and/or a primary air regulator (19) and/or a door (15), and wherein the event related to the start switch thereby also relates to the primary air damper, regulator or the door.

In an advantageous embodiment the temperature sensor is exposed to temperatures below 450 degree C, preferably below 400 degree C, even more preferably below 350 degree C. In an advantageous embodiment said combustion monitoring system comprises a wireless transceiver, preferably a Bluetooh LE transceiver, for transmitting said temperature representation to said output device, preferably a Bluetooth-enabled mobile device such as a smartphone or tablet or laptop computer. The present invention further relates to a wood-burning stove (1) comprising a combustion chamber (11) defined by an inner stove (12), the inner stove having an outside (121), the wood-burning stove further comprising a combustion monitoring system (2), the combustion monitoring system comprising

a temperature sensor (22) arranged substantially at said outside (121) of the inner stove (12), and

a processing and communication arrangement (21) being coupled to said temperature sensor (22) and further providing a communicative coupling (23) for enabling connection to an output device (24), wherein the temperature sensor is arranged to provide a temperature sensor output during combustion of said solid fuel, and wherein the processing and communication arrangement is arranged to transmit temperature representations relating to the combustion of solid fuel inside said combustion chamber to the output device, the temperature representations being derived from the temperature sensor output, and wherein the output device is arranged with a software application to process said temperature representations to provide an output based on said temperature representations.

The present invention further relates to a combustion monitoring system (2) comprising

a temperature sensor (22) adapted for arranging at an outside (121) of an inner stove (12) defining a combustion chamber (11) of a wood-burning stove (1),

a processing and communication arrangement (21) adapted for providing temperature representations on the basis of temperature sensor output received from the temperature sensor,

a software application adapted to be executed by an output device (24) and when executed to make the output device establish a communicative coupling (23) with the processing and communication arrangement,

to receive the temperature representations, and

to processes said temperature representations to provide an output at the output device based on said temperature representations.

The combustion monitoring system of the present invention is highly advantageous, relevant and helpful, relatively inexpensive, very easily installed or retrofitted, and easily used by anyone with a smartphone or tablet computer.

In an advantageous embodiment the combustion monitoring system further comprises a start switch (25), preferably mechanically coupled to a primary air damper (14) and/or a primary air regulator (19) and/or a door (15) of the wood- burning stove (1).

In an advantageous embodiment the combustion monitoring system is arranged to be retrofitted to wood-burning stoves, preferably non-invasively retrofitting with respect to the combustion chamber and inner stove. The present invention relates to a method of retrofitting a combustion monitoring system (2) as described above to a wood-burning stove (1), said method comprising arranging a temperature sensor (22) substantially at an outside (121) of an inner stove (12) defining a combustion chamber (11) and providing a processing and communicating arrangement (21) coupled to the temperature sensor (22), the method comprising performing said retrofitting non-invasively with respect to said combustion chamber and said inner stove.

In an advantageous embodiment the combustion monitoring system comprises a timing unit to associate said temperature representations with timestamps. In order to not only being able to monitor but also to predict how the combustion will develop and in particular at which time certain combustion zones will be reached, most particularly estimate when it will be the optimal time to refuel the stove, it is very advantageous to have the temperature measurements associated with timestamps. In a preferred embodiment the timestamps are transmitted to the output device together with the temperature representations, in particular if the temperature representations are not transmitted at the time of acquisition but are delayed and/or grouped together for fewer transmissions or for catching up after a period of unavailability of the output device.

In an advantageous embodiment said temperature sensor is a sensor of a thermocouple or resistor temperature detector (RTD) type. In a preferred embodiment the temperature sensor is for example a type "K" thermocouple.

In an advantageous embodiment the temperature measured by said temperature sensor, during combustion of solid fuel, is lower that the internal temperature in the upper part of said combustion chamber.

In an advantageous embodiment said output device processes said received temperature representation together with further wood-burning stove depending parameters In an advantageous embodiment said output device present combustion-related information to a user of said output device.

In an advantageous embodiment said combustion-related information comprises an estimated time for optimally refilling the combustion chamber with solid fuel such as wood.

In an advantageous embodiment said combustion-related information comprises suggestions to the user to adjust air flow to the combustion chamber. In an advantageous embodiment said output and/or combustion-related information at least partly depends on the specific type of wood-burning stove in which said combustion is performed. In an advantageous embodiment said combustion-related information is at least partly based on experiential information relating to a temperature development in a predefined type of wood-burning stove dependent of the amount of solid fuel used for combustion.

In an advantageous embodiment said combustion-related information comprises chimney draft related information. In an advantageous embodiment said specific type of wood-burning stove is selected from a predefined list of different wood stoves.

In an advantageous embodiment said combustion monitoring system is battery powered.

In an advantageous embodiment the combustion monitoring system measures and transmits the temperature representation at a predefined interval to said output device, e.g. determined by a timer function, the interval preferably being less than 1 minute, even more preferably less than 30 seconds, and most preferably about 10 seconds.

The drawings

The invention will in the following be described with reference to the drawings where figs. 1 - 2 illustrate embodiments of the invention with temperature sensor outside the combustion chamber,

fig. 3 illustrates an embodiment of the invention with a start switch,

fig. 4 illustrates an embodiment of the invention with a start switch and primary air regulator,

fig. 5 - 9 illustrate an embodiment of the invention, in particular the simplicity of retrofitting, and

fig. 10 illustrates a screen from a smartphone app according to an embodiment of the invention.

Detailed description

Fig. 1 illustrates an embodiment of the invention. It illustrates a wood-burning stove 1 with a combustion chamber 11. The wood-burning stove is preferably of the convection type where surrounding air is heated and thereby made to circulate between an inner stove 12 and an outer covering, of which for reasons of simplicity only an outer covering top 161 and an outer covering bottom 162 are illustrated.

The inner stove 12 preferably comprises a baffle 122 and a primary air intake 13. A primary air damper 14 is preferably provided to facilitate regulation of the primary air flow, for example by arranging the primary air damper 14 in a sliding manner with primary air damper vents 141 corresponding to vents of the primary air intake 13, so that sliding the primary air damper 14 as indicated by the arrows will dislocate or align the primary air damper vents 141 away from or with, respectively, the vents in the primary air intake 13. In a preferred embodiment additional air intakes, e.g. so- called secondary air intakes, are further provided at different locations of the stove for facilitating fine control of the air flow.

The wood-burning stove 1 further comprises a door or opening arrangement 15, providing access to the combustion chamber for firing and refilling firing wood, and a chimney 17 coupled to an exhaust opening 18 of the inner stove 12.

The illustrated wood-burning stove is merely sketched in principle with the features that facilitate the description of the present invention. A person skilled in the art of wood-burning stoves will appreciate that several alternative principles and variations on stoves are known and within the scope of the present invention. In particular it should be noted that the present invention, within its scope, also applies to radiation stoves as well as convection stoves, stoves with alternative primary air intakes, e.g. at the front, sides or rear instead of or in addition to the illustrated bottom vents, alternative primary air dampers or regulators, e.g. a damper located in an air intake through the outer cover or in an air duct instead of in direct cooperation with vents in the inner stove, alternative or additional baffle configurations, additional air intakes and air or flue gas regulators or dampers, any door or opening arrangement, with or without additional air flow features, etc.

The embodiment of Fig. 1 further comprises a combustion monitoring system 2 according to an embodiment of the invention. The combustion monitoring system 2 comprises a processing and communication arrangement 21, a temperature sensor 22 and a temperature sensor wire 221.

The processing and communication arrangement 21 is preferably battery-driven, but may in an embodiment comprise a different power supply, such as a mains-driven power supply, or it may be driven by alternatively generated electricity, e.g. generated by heat from the stove, e.g. by means of thermocouples or thermopiles.

The temperature sensor 22 is located at an outside 121 of the inner stove 12, preferably near the exhaust opening 18, e.g. immediately adjacent to the chimney 17 or within a few centimetres. The temperature sensor may be fastened to the outside 121 of the inner stove by magnetic force, bolts, temperature resistant glue, etc., or, in stoves with an outer covering 16, 161, e.g. convection stoves, the temperature sensor may be fastened by wedging, squeezing or clamping the sensor or a fitting or other mounting in or on which the sensor is fixed into the narrow space between the inner stove and the outer covering, e.g. by fixing the sensor to a suitably shaped spring metal or other material, e.g. a bended sheet metal which in the direction of spring force has a dimension greater than the distance between the inner stove and the outer covering, but which when inserted in the narrow space becomes compressed in the direction of spring force and thereby is wedged sufficiently firmly to hold the temperature sensor in place.

The temperature sensor is preferably of the thermocouple type, preferably a type "K" thermocouple, but any temperature sensitive component, e.g. a thermocouple, a resistor temperature detector (RTD) or a thermistor with appropriate temperature range of operation according to the location on the stove, may be used. A person skilled in the art of converting absolute or relative temperature to an electrical characteristic (voltage, current or resistance) will appreciate the wide range of temperature sensor technologies applicable within the scope of the invention, as well as their practical implementation to measure stove outside temperatures. In a preferred embodiment the temperature sensor wire 221 transfers a raw analog sensor output signal, e.g. a voltage difference established by applying a fixed current through an RTD or a potential generated by a thermocouple, to the processing and communication arrangement 21, which preferably comprises circuitry arranged to convert and process the sensor output signal. The circuitry may e.g. comprise operational amplifiers, current and/or voltage sources, voltage dividers, etc. In a preferred embodiment the circuitry consists of a dedicated integrated circuit appropriate for the sensor type, e.g. a thermocouple amplifier with voltage or digital output or an RTD-to-voltage or RTD-to-digital integrated circuit. If the result is represented by a voltage range, the conversion circuitry may preferably also comprise an analog-to-digital converter (A/D-converter) to allow digital processing of the detected temperature.

Alternatively, circuitry as mentioned above for converting the sensor output signal to a suitable analog range, e.g. 0 - 5V, or to a digital signal, e.g. 16 bit pulse code modulated (PCM), may be integrated with the temperature sensor 22, and the temperature sensor wire 221 be used to transfer the converted value to the processing and communication arrangement 21 for direct processing.

The processing and communication arrangement 21 may be located anywhere, but may advantageously be located on a rear, outer covering, e.g. by magnets, for easy access for battery replacement or operation of any buttons. The processing and communication arrangement preferably comprises a processor of any suitable kind and a semiconductor memory, preferably a non-volatile but writable memory, e.g. an EEPROM or flash memory, for storing measured temperatures together with time of measurement. The processing and communication arrangement 21 further comprises a communication interface for establishing a communicative coupling 23 to provide the measurement data and/or processed conclusions to an output device 24 or receive control information. The output device 24, which may in a preferred embodiment also be used as an input device, preferably comprises a smartphone, but alternatively it may be a tablet, laptop or desktop computer, a computer monitor or other display, a traditional text message enabled cell phone, an advanced universal remote control, etc., or it may be a dedicated output device manufactured or adapted specifically for use with the combustion monitoring system 2. The communication interface is preferably a Bluetooth interface, even more preferably a Bluetooth Low Energy (Bluetooth LE) interface, which is very well suited for power-efficient short range communication with smartphones. Any other suitable communication interface is within the scope of the invention, e.g. wireless interfaces such as e.g. WiFi (WLAN or WiFi Direct) or other short range radio communication technologies, GSM or other cell phone communication technologies, e.g. more specifically use of an SMS or data service, near-field communication NFC, infrared communication, e.g. using IrDa protocols, etc., or wired interfaces such as e.g. USB, FIDMI, DisplayPort, etc.

The processing and communication arrangement 21 may in an embodiment comprise a user interface e.g. comprising one or more buttons or knobs, e.g. to reset or initialize the combustion monitoring system 2, set reference values, etc.

In a preferred embodiment all or most user interaction is performed by means of the output device 24, preferably by means of a smartphone application, a combustion monitoring app 241, specifically adapted for use with the combustion monitoring system of the present invention and communication with the processing and communication arrangement 21 via the communicative coupling 23.

The processing and communication arrangement 21 preferably comprises a temperature sensor circuit receiving the temperature sensor wire 221 and converting the signal to a temperature representing voltage, and a Bluetooth LE integrated circuit system which besides the Bluetooth functionality further comprises a microcontroller for carrying out the processing, analog voltage inputs and A/D converters for converting the temperature representing voltage to a digital temperature value and monitoring battery voltage, and an EEPROM memory or flash memory for storing temperature measurements and settings, e.g. user-defined system identification name.

The combustion monitoring system 2 is arranged to maintain a relationship between temperature and time, so as to facilitate a time-dependent monitoring of the temperature, and to facilitate making analysis and provide advice based on the temperature development during a burning. The time stamping of temperature measurements or other mapping of measured temperatures to time is preferably provided by the processing and communication arrangement 21, whereas the use of the time-temperature relationship is preferably taking place in the output device 24, preferably by the combustion monitoring app 241.

The relationship between the actual combustion and the temperature measured by the temperature sensor at the outside of the combustion chamber for a specific stove model may preferably be established by analysing and correlating combustion chamber outside temperatures, e.g. measured by the combustion monitoring system 2 of the invention, with inside temperatures, e.g. measured with an additional temperature sensor, during a number of burnings, e.g. 5 - 200 burnings, preferably a considerable number of burnings such as e.g. 100 burnings. This calibration process is preferably performed by a stove manufacturer for each stove model for which a combustion monitoring system 2 should be mounted or made available for retrofitting.

Fig. 2 illustrates an embodiment similar to that described above with reference to Fig. 1, the description thereof applying, mutatis mutandis, to the embodiment of Fig. 2. The difference is that in the embodiment of Fig. 2 the exhaust opening 18 and chimney 17 are configured at the rear side of the wood-burning stove 1, and the temperature sensor 22 is located at the outside 121 of the inner stove 12, preferably near the exhaust opening 18, e.g. immediately adjacent to the chimney 17 or within a few centimetres. The temperature sensor may be fixed with generally any of the same methods as described above with reference to Fig. 1.

Fig. 3 illustrates an embodiment similar to that described above with reference to Fig. 1, the description thereof applying, mutatis mutandis, to the embodiment of Fig. 3. This embodiment further comprises a start switch 25 connected to the processing and communication arrangement 21. The start switch may be arranged for user operation, e.g. by means of a pushbutton on the front of the stove, a coupling with the stove door, or may preferably as illustrated in Fig. 3 be arranged in correspondence with e.g. a primary air damper 14 in such a way that the state of the start switch 25 is changed when the primary air damper 14 is pulled out to provide free access for air through the primary air intakes 13. As primary air should preferably be added for a few minutes upon firing up the stove or adding wood, a correspondence between the primary air damper 14 and the start switch 25 may be used to signal to the processing and communicating arrangement each time new wood is placed in the combustion chamber 11. In the embodiment of Fig. 3 the start switch 25 is a simple circuit breaker which, due to a suitable flange added to the primary air damper 14, breaks the circuit facilitated by a start switch wire 251 when the primary air damper is pulled out, and closes the circuit when the primary air damper is pushed in. In a preferred embodiment the combustion monitoring system uses this information to trigger the temperature monitoring, preferably by starting the monitoring when the start switch indicates that the primary air damper has been pulled out. In a preferred embodiment, the triggering of the start switch causes a new monitoring session and resets the temperature-monitor time to zero, so that a new time-temperature curve may be produced. A person skilled in the art of switches and detectors will appreciate that there are numerous ways, including numerous switch or input configurations, of establishing and providing a signal to the processing and communication arrangement at the time of firing up or adding wood in order to trigger the start or restart of temperature monitoring, which are within the scope of the invention. Fig. 4 illustrates an embodiment similar to that described above with reference to Figs. 1 and 3, the descriptions thereof applying, mutatis mutandis, to the embodiment of Fig. 4. This embodiment further comprises a primary air regulator 19, which in the specific illustrated embodiment comprises a cylinder with a spring-biased plunger cooperating with the primary air damper 14 to automatically slide the primary air damper to a position with little or no primary air flow subsequent to a manual sliding out the primary air damper to increase primary air flow. An adjustable valve for only letting air into the cylinder very slowly facilitates extending the plunger travelling time for several minutes, e.g. 5 - 7 minutes. During this time, in a preferred embodiment, the primary air flow will decrease gradually from full flow to no or little flow. If more time is needed with increased air flow, e.g. during starting a fire in a cold stove, the primary air damper may be fixed in the fully open position, thereby preventing the primary air regulator 19 from closing it. Even though the present invention is herein described with reference to embodiments using a spring- and vacuum-biased plunger as primary air regulator, any suitable primary air regulator 19 for automated decrease of primary air flow after refilling of wood, is within the scope of the invention. The combination of an automatically closing primary air damper and configuring the start switch so that its state depends on the state of the primary air damper, makes the start switch automatically reset to a state where each refuelling is detected by the start switch and thereby usable in the processing and communication arrangement for e.g. restarting the monitoring.

Figs. 5 - 9 illustrate an embodiment of the present invention similar to the embodiments described above with reference to Figs. 1 - 4, the description there applying to the embodiments of Fig. 5 - 9, mutatis mutandis. In Figs. 5 - 8 the outer covering 16 and the outer covering top 161 have been removed in order to retrofit a combustion monitoring system 2 according to the present invention, comprising a processing and communication arrangement 21, a temperature sensor 22, a temperature sensor wire 221, a start switch 25 and a start switch wire 251 to the wood-burning stove 1. The easy retrofitting property of the present invention is partly produced from the non-invasive nature: according to the present invention no temperature sensor or other sensors need to be integrated in the combustion chamber 11, but can simply be mounted on the outside of the combustion chamber, or even on the outer covering 16. In a preferred embodiment using a smartphone as output device 24, the retrofitting procedure may further comprise installing the combustion monitoring app 241 on the smartphone and establish the communicative coupling 23.

Fig. 10 illustrates an example of a main screen of a combustion monitoring smartphone app. The specific instance of a view shown in Fig. 10 informs the user that the communicative coupling with the processing and monitoring arrangement is established, that the battery is still in good condition, that the best time to supplement with new wood to the stove is in 45 minutes, and if that is not achieved, then the latest time to add the wood will be in 60 minutes. The screen further shows the measured temperature development for the current logging session, i.e. since last reset by the start switch, mapped upon a diagram illustrating the different combustion quality zones with respect to temperature and time. The diagram is based on estimated combustion behaviour for the particular setup of stove, chimney and amount of wood used.

In a preferred embodiment, if the connection to the processing and communication arrangement 21 is lost, e.g. because the user takes the smartphone with him away from the house, the combustion monitoring smartphone app may convert the duration until the optimal refuelling, e.g. 45 minutes, to an estimated time for the next refuelling, e.g. 10.37 a.m., and possibly set this time as an alarm in the smartphone.

Upon return of the smartphone into transmission distance, the smartphone app may get all or a summary of meantime measurements transmitted from the storage memory of the processing and communications arrangement in order to update the illustrated combustion development and recalculate estimated combustion zones, in particular the estimated time for optimal refuelling. In a preferred embodiment of the invention the activities performed by the processing and communication arrangement 21 comprise the following: Al . Staying in sleep mode, i.e. low power consumption mode, until start switch is activated by user opening the primary air damper.

A2. Logging temperatures from the outside of the combustion chamber frequently, e.g. every 10 seconds, and store in non- volatile memory.

A3. Keep logging temperatures for a considerable time, e.g. 4 hours, since the last activation of the start switch.

A4. Start a new logging session each time the start switch is activated. Depending on available memory and logging frequency, a number of previous sessions are preferably stored, preferably e.g. 2 previous sessions together with an active session. A5. Monitor battery voltage regularly, e.g. every 30 minutes.

A6. Accept Bluetooth connection from at least one output device, i.e. preferably a Bluetooth LE enabled smartphone.

A7. Continually transmit active session data and battery status to smartphone app. In a preferred embodiment the processing and communication arrangement 21 may be adapted to also perform special tasks besides the above-described normal operation, e.g. :

Bl . Change Bluetooth identification name of the communication interface upon request, preferably by allowing a smartphone app user to define a new identification name. This is particularly relevant if the same user monitors and controls two or more stoves by the same smartphone.

B2. Manage saved temperature log files, e.g. export to a smartphone app user or delete. In a preferred embodiment the combustion monitoring smartphone app may be arranged to initialize itself at first use by performing the following steps:

CI . Request the user to select a predetermined combustion scheme, preferably by presenting the user with a list of supported wood-burning stoves and letting the user select the relevant stove, and have each stove associated with a predetermined combustion scheme.

C2. Optionally show installation instructions for how to mount the combustion monitoring system to the selected particular wood-burning stove. C3. Connect the smartphone to the processing and communication arrangement by Bluetooth LE.

C4. Guide the user through a chimney test in order to determine how the particular stove installation affects the predetermined combustion scheme, probably measured at the manufacturers place. The chimney test preferably involves requesting the user to burn a particular weight of wood within a certain humidity range in his stove with particular damper settings, etc., and having the combustion monitoring app monitoring the temperature development. The effect of the particular chimney may preferably be decided based on the maximum temperature achieved during the chimney test, e.g. for a particular stove determining the chimney to be a low effect chimney if largest measured temperature was in the range of 190 - 239 degree C, a normal effect chimney if max temperature in the range of 240 - 269 degree C, and a high effect chimney if max temperature from 270 degree C and up. In a preferred embodiment use of a wood-burning stove with a combustion monitoring system according to the present invention guided by the combustion monitoring smartphone app may preferably involve the following normal operation steps:

Dl . Connect to the processing and monitoring arrangement of the stove.

D2. Optionally, but preferably, the user inputs the approximate amount of wood used at a time. This may be set as a standard user preference value, or input for each refill.

D3. Optionally, but preferably, the user inputs the effect class of the particular setup of wood-burning stove and chimney, preferably simply by choosing among low, medium or high effect stove setups. The relevant effect class depends on the chimney effect as determined by the chimney test described above, and the effect setting of the stove if applicable to the particular stove. The combined effect class may be set as a standard user preference value, or input for each refill.

D4. Continually receive temperature and battery data

D5a. If the measured temperature on the outside of the combustion chamber is below a certain minimum, e.g. 100 degree C, assume that the stove is starting up from a cold state and postpone further calculations and guidance until temperature reaches e.g. 200 degree C; then request user to unlock the primary air damper so that it will return to closed state within a few minutes if the stove is provided with a primary air regulator as described above with reference to Fig. 4.

D5b. If the measured temperature is above, e.g., 100 degree C from the beginning, assume that new wood has been added to burning stove, and commence calculation and guiding.

D6. Display an assumed time to next refill, based on the predetermined combustion scheme and/or past experience for a certain amount of time until the measured temperature variation attains a negative coefficient or until a predetermined time has passed, e.g. between 30 minutes and 60 minutes, depending on the particular stove. D7. Calculation of estimated refill time t based on actual temperature measurement may be determined by the following equation:

, where

T ₀ = measured temperature,

T _t = target temperature, e.g. 150 degree C for ideal refill time, and e.g. 110 degree C for latest refill time, i.e. just above the minimum temperature for considering it a cold start, the target temperature depends on the particular wood-burning stove and the location of the temperature sensor,

T _a = a constant, e.g. in the amount of around 100

k = a constant, e.g. in the amount of around 0.0004

Both constants are selected by a lookup-table or a formula in dependency of the particular stove and preferably information about the amount of solid fuel put into the combustion chamber at the last refill. The constants may be set based on past experience or measurements performed by the manufacturer.

The above calculations of refill times are preferably updated for each new temperature measurement, e.g. each 10 seconds.

D8. Determine if the currently measured temperature falls within a bad combustion zone, see illustration in Fig. 10, and display suggestions to the user for countermeasures, e.g. set stove to higher effect, increase flow of primary air, etc. D9. Display suggestions for optimal restart if the measured temperature has dropped below minimum limit, e.g. 110 degree C. D10. Restart procedure when new temperature logging session starts, i.e. triggered by start switch on the stove, e.g. in the embodiments of fig. 3 and 4 when user refills stove and pulls out primary air damper. An example of assumed refill times to use for the temperature rising phase described in step D6 above, for a particular wood-burning stove is provided by the following table 1 :

Wood amount: 1.5 kg

Effect Wait time before Assumed duration Minimum Assumed duration class going to step D7 to optimal refill temperature for latest refill

[minutes] [minutes] Tmin [minutes]

(T = 150 degree C) [Celcius] (T = Tmin)

High 33 78 110 133

Med 40 78 110 133

Low 50 80 120 112

Wood amount: 2.0 kg

Effect Wait time before Assumed duration Minimum Assumed duration class going to step D7 to optimal refill temperature for latest refill

[minutes] [minutes] Tmin [minutes]

(T = 150 degree C) [Celcius] (T = Tmin)

High 37 92 110 143

Med 43 93 110 145

Low 53 95 120 145

Wood amount: 2.5 kg

Effect Wait time before Assumed duration Minimum Assumed duration class going to step D7 to optimal refill temperature for latest refill

[minutes] [minutes] Tmin [minutes]

(T = 150 degree C) [Celcius] (T = Tmin)

High 37 100 110 167

Med 43 103 110 170

Low 53 107 120 142 Wood amount: 3.0 kg

Effect Wait time before Assumed duration Minimum Assumed duration class going to step D7 to optimal refill temperature for latest refill [minutes] [minutes] Tmin [minutes]

(T = 150 degree C) [Celcius] (T = Tmin)

High 40 117 110 183

Med 47 122 110 188

Low 57 125 120 163

Table 1

It is noted, that alternatives and variations of the above-described procedures values are within the scope of the present invention.

List of reference numbers

1 wood-burning stove

11 combustion chamber

12 inner stove

121 outside of inner stove

122 baffle

13 primary air intake

14 primary air damper

141 primary air damper vents

15 door or opening arrangement

16 outer covering

161 outer covering top

162 outer covering bottom

17 chimney

18 exhaust opening

19 primary air regulator

2 combustion monitoring system

21 processing and communication arrangement

22 temperature sensor

221 temperature sensor wire

23 communicative coupling

24 output device

241 combustion monitoring app

25 start switch

251 start switch wire