Abstract: A fan drive circuit for a variable speed fan motor in a cooling system, includes an inverter configured to supply a current signal to stator windings of the variable speed fan motor, a frequency detection circuit coupled to an output stage of an inverter of a compressor motor of the cooling system and configured to detect a first frequency of a compressor current signal at the output stage of a variable speed compressor drive circuit and generate a frequency signal, and a digital signal processor (DSP) coupled to the inverter and the frequency detection circuit. The DSP is configured to receive the frequency signal corresponding to the first frequency from the frequency detection circuit, select a second frequency corresponding to the first frequency at which to operate the variable speed fan motor, and transmit control signals to the inverter to supply current to the stator windings at the second frequency.

Abstract: A thermal imaging system including at least one thermal imaging device, a server, and at least one mobile device. The thermal imaging device captures thermal images of an environment. The server applies computer vision techniques to the thermal images, detects events of a predetermined type, and generates notifications of the events of predetermined types detected from the thermal images. The mobile device runs a mobile application that is configured to receive the notifications, present user interfaces, receive user annotations of the notifications in the user interfaces, and transmit the annotations to the server. According to the annotations, the server adjusts parameters used in the application of the computer vision techniques and in the generation of the notifications.

Abstract: A heating system is configured to optimize the speed and accuracy of the system in achieving various ambient air temperature setpoints, by modulating the heated water supply water setpoint to optimize the slope of the system's response curve. Optimized response curves are automatically determined by analyzing differences between ambient air temperatures over time in response to modulated supply water temperatures as they are reset upward or downward to achieve response times prioritized for improved occupant comfort. The controller of the heating system calculates a temperature slope, and adjusts the supply water setpoint to increase/decrease the speed of ambient temperature rise to achieve a desired slope.

Abstract: An apparatus for controlling a level of oxygen in a closed environment from an oxygen supply having an oxygen sensor for detecting the level of oxygen in the closed environment. The apparatus has a plurality of relays in communication with the sensor. The apparatus has a valve in communication with the relays and the oxygen supply which is automatically opened with the relays without human interaction, monitoring and adjustment to release oxygen from the oxygen supply into the environment when the level of oxygen in the environment goes below a first predetermined level and which is automatically closed with the relays without human interaction, monitoring and adjustment to stop oxygen from being released from the oxygen supply into the environment when the level of oxygen in the environment goes above a second predetermined level. A method for controlling a level of oxygen in a closed environment from an oxygen supply. A refuge chamber.

Abstract: A fresh-air cooling system for a building structure having an unvented attic is provided. The system provides airflow pathways that allow outside air to be drawn through, and discharged from, a building having an unvented attic. Dampers with a low thermal conductivity regulate airflow through the building structure. The system allows a whole house fan to cool a building having an unvented attic. The system seals or otherwise alters airflow pathways through the building structure in order to reduce heat transfer between the building and the outside environment when the cooling system is not in use.

Abstract: A device is configured to operate a Heating, Ventilation, and Air Conditioning (HVAC) system. The device is further configured to determine that the amount of time to ignite a burner in a burner assembly has exceeded a time threshold value and that a flame was not detected by a flame sensor. The device is further configured to receive an audio signal from a microphone while operating the HVAC system, to identify an audio signature for the flame, and to determine whether the audio signature for the flame is present within the first audio signal. The device is further configured to determine a fault type based on the determination of whether the audio signature for the flame is present within the audio signal, to identify a component identifier for a component of the HVAC system that is associated with fault type, and to output a recommendation identifying the component identifier.

Abstract: The present disclosure relates to the field of air conditioning technology. In particular, it involves an air control method for air handler unit.

Abstract: The invention involves the automated testing of HVAC units using an energy management system. The automated HVAC test is performed to understand if one or more HVAC units are operational across one or more locations. If an HVAC unit is not operational, HVAC testing could be performed to understand which component or stage of the HVAC unit is not working as designed. The automated HVAC test is also used to calculate the efficiency of the HVAC unit(s) being tested. The various HVAC tests are performed on all HVAC units as a form of preventative maintenance and diagnostics. These tests can be scheduled on-demand, for a future date and time, or on a recurring schedule (monthly or quarterly). A report is generated for each HVAC test and can be viewed and exported from a cloud-based energy management platform.

Abstract: A method for controlling a gas furnace that performs a heating operation by receiving a first heating signal; calculating a certain heating capacity smaller than a maximum heating capacity of the gas furnace, according to the first heating signal; and operating a heating of the gas furnace with the calculated certain heating capacity. The calculating of the certain heating capacity includes calculating the certain heating capacity according to a difference between an intake air temperature sucked into the gas furnace and a reference temperature.

Abstract: A computer-implemented method is provided of controlling a heating, ventilation, and air-conditioning (HVAC) system having a heat pump and an auxiliary heater to heat an inside zone, the method comprising: setting values for an economic balance point and a temperature set point; setting a capacity balance point to be equal to the economic balance point; measuring an initial inside temperature in the inside zone and an outside temperature outside of a structure containing the inside zone; determining that the initial inside temperature is lower than the temperature set point; determining that the outside temperature is greater than the capacity balance point; activating the heat pump to heat the inside zone; waiting a heating interval while the heat pump is active; determining that the heat pump is not effective in heating the inside zone; and setting the capacity balance point to be equal to the outside temperature.

Abstract: A method and an apparatus for protection of a combustion unit of a chemical process against over firing, the burner(s) of the combustion unit are limited by a fuel and duty limiter which limits the duty based on process feeds, combustion gas and fuel flows.

Abstract: A method for operating a temperature control system is disclosed. The method includes monitoring an interior and exterior temperature of a structure, defining a first time range and a second time range, associating one or more operating parameters of the temperature control system with the first time range, associating one or more operating parameters of the temperature control system with the second time range, monitoring operational time and operational load of the cooling system for the first time range, predicting a space temperature and an outdoor air temperature for a subsequent time period, and controlling a ventilation subsystem during the second time range based upon the monitored operational time and operational load of the cooling subsystem for the first time range, the predicted space temperature, the predicted outdoor air temperature, and the one or more operating parameters of the cooling subsystem associated with the second time range.

Abstract: Embodiments relate generally to power conversion systems. The system may include an inverter subsystem, inverter housing assembly, and processing subsystem. The inverter subsystem may include an input section for receiving input DC voltage and output section for providing output AC voltage. The inverter housing assembly may include side walls, main cavity, air inflow section, and air outflow section. The main cavity may be formed so as to house the inverter subsystem and form a ventilation channel. The air inflow section may be for use in allowing an inflow of air. The air outflow section may be for use in allowing an outflow of air. The processing subsystem may include a monitoring assembly and communication assembly. Monitoring assembly may be electrically connected to the inverter subsystem and configurable to perform measurements. Communication assembly may be in communication with the monitoring assembly, and configurable to communicate measurements performed by the monitoring assembly.

Abstract: Disclosed herein are related to a system, a method, and a non-transitory computer readable storing instructions for operating an energy plant comprised of heating, ventilation and air conditioning (HVAC) devices. In one aspect, the system generates gradient data indicating a gradient of operating performance of the energy plant with respect to values of a plurality of control variables of HVAC devices. The system determines, from the plurality of control variables, a reduced group of control variables of the HVAC devices based on the gradient data. The system determines a set of values of the reduced group of control variables. The system operates the energy plant according to the determined set of values of the reduced group of control variables.

Abstract: A method for operating a refrigeration unit that includes controlling overall compressor output of the refrigeration unit having at least one state variable. The method includes operating the compressor unit either in a first mode with a first overall compressor output in which the state variable decreases or in a second mode with a second overall compressor output in which the state variable increases, wherein the first and second modes alternate. The method further includes transitioning from the second mode to the first mode when the measured state variable reaches or exceeds a first threshold, and transitioning from the first mode to the second mode when the measured state variable reaches or falls below a second threshold. The difference between the first value and the second value corresponds to the greatest of the state variable differences that result over the respective minimum duration in the first or second mode.

Abstract: A method for controlling an air handler including a fan, a heater and/or a compressor, by installing an energy saving controller between a thermostat and the air handler, shutting down the compressor or heater for a first predetermined duration if the compressor or heater has run continuously for a second predetermined duration during the current cycle, while allowing the fan to run for a fan's first run time extension amount equal with the first predetermined duration.

Abstract: In a method for superimposed conveyance of data and electrical power, a first switch can cycle to convey the electric power and data from a first device. Binary digits of the data from the first device can be represented by transitions, of a voltage at a node of a second device, between a first voltage and a second voltage. A second switch can cycle to convey data from the second device. Binary digits of the data from the second device can be represented by transitions, of a current through a component of the first device, between being less than a threshold and being greater than the threshold. A voltage regulator of the second device can provide, in response to the voltage at the node being within a range of voltages that includes the first voltage and the second voltage, the electrical power to one or more components.

Abstract: A controller for a gas furnace, a computer-usable medium for implementing a method and a gas furnace are disclosed herein. In one embodiment, the controller includes: (1) an interface configured to receive a heating call and (2) a processor configured to enable an inducer of the gas furnace at a low speed based on the heating call and ignite the gas furnace at a high fire operation when determining a low fire pressure switch of the gas furnace is open.

Abstract: A process and apparatus for disinfection of spaces using a disinfecting liquid droplet spray atomization are described, in which an electric fan 107 is used to dispense the atomization from an atomization chamber 104 via venture outlets 106 into the space to be disinfected. The operation of the electric fan 107 is modulated in a substantially random sequence to vary the rate of dispensing into the space in order to improve the dispersal of the atomized droplets in the space and hence the efficacy of disinfection.

Abstract: A purge time of a combustion space is optimized in a multi-burner system having a combustion chamber in which the combustion space is physically separated from a heating space by providing a combustion controlling device. The combustion controlling device controls an operation of multiple burners having combustion spaces different from each other, a first prepurge time and a second prepurge time set as execution times of a single purge, the single purge based on the first prepurge time is performed on a combustion space of a corresponding burner after overall purge when an ignition of the burner is instructed in a state where none of the burners is ignited, and the single purge based on the second prepurge time is performed on the combustion space of the corresponding burner when the ignition of the burner is instructed in a normal operating state.

Abstract: Systems and methods for delaying or activating a blowout device in a sampling pipe network of an aspirated smoke detection system are provided. Some systems can include an aspirated smoke detector, a sampling pipe coupled to the aspirated smoke detector, a blowout device coupled to the sampling pipe, and a delay device coupled to the blowout device. Responsive to the aspirated smoke detector detecting a triggering event, the delay device can delay the blowout device from performing a blowout action in the sampling pipe or can instruct the blowout device to perform the blowout action in the sampling pipe.

Abstract: An outdoor device of an air conditioner includes a compressor, an outdoor fan, and an outdoor control board. The outdoor device includes: a control unit that controls the compressor and the outdoor fan; and a temperature detector that detects an ambient temperature of an electric component provided on the outdoor control board. The control unit, when the compressor is stopped, stops the outdoor fan and then determines whether a temperature detected by the temperature detector is equal to or higher than a threshold, and, when it is determined that the temperature detected by the temperature detector is equal to or higher than the threshold, operates the outdoor fan at a protective rotation number that is lower than a rotation number of the outdoor fan while the compressor is in operation so as to circulate air, thereby cooling the outdoor control board.

Abstract: A method includes: outputting high side driver gate signals to a plurality of high side driver devices and outputting low side driver gate signals to a plurality of low side driver devices configured to control current supplied to a motor having coils coupled to receive the current at a plurality of phase nodes; at a time approximately prior to an expected zero crossing of a voltage at a selected one of the plurality of phase nodes, disabling the high side driver gate signal and the low side driver gate signal; measuring a back electromotive force (BEMF) voltage and observing a zero crossing time; estimating a next zero crossing time; prior to the next zero crossing time, disabling the high side driver gate signal and the low side driver gate signal and observing the selected one of the phase nodes to form a first sample; and following the next zero crossing time, observing a second voltage at the selected one of the phase nodes to form a second sample.

Abstract: The disclosure provides a proportional control signal circuit (PCSC), an HVAC controller employing the same and an HVAC system including the HVAC controller. In one embodiment, the PCSC includes: (1) a signal input configured to receive a pulse width modulated signal, (2) a control input configured to receive an integration signal, (3) a signal output and (4) control circuitry, coupled to the signal input, the control input and the signal output, configured to provide either the pulse width modulated signal or a DC signal to the signal output based on the integration signal.

Abstract: An air moving appliance comprising an electric motor coupled to a fan, a control system for controlling the motor, the control system including monitoring means configured to monitor a motor load parameter; memory means configured to store a predetermined reference motor load parameter value; compensating means that determines a compensated reference motor load parameter value based on the predetermined reference motor load parameter value and a set of ambient environment input conditions; comparison means configured to compare the motor load parameter and the compensated reference motor load parameter value and trigger an operational event based on the result of the comparison. The invention also relates to a method of controlling an air moving appliance.

Abstract: A controller for a gas furnace, a computer-usable medium for implementing a method and a gas furnace are disclosed herein. In one embodiment, the controller includes: (1) an interface configured to receive a heating call and (2) a processor configured to enable an inducer of the gas furnace at a low speed based on the heating call and ignite the gas furnace at a high fire operation when determining a low fire pressure switch of the gas furnace is open.

Abstract: An HVAC system having an air cleaner, a fan configured to selectively generate an air flow, wherein at least a portion of the air flow is passed through the air cleaner, and a controller configured to control the air cleaner in response to at least one of a setting for controlling the fan and an operation characteristic of the fan is disclosed.

Abstract: A controller for a gas furnace, a computer-usable medium for implementing a method and a gas furnace are disclosed herein. In one embodiment, the controller includes: (1) an interface configured to receive a heating call and (2) a processor configured to enable an inducer of the gas furnace at a low speed based on the heating call and ignite the gas furnace at a high fire operation when determining a low fire pressure switch of the gas furnace is open.

Abstract: A control system is disclosed for a house HVAC system including a thermostat, supply and return air plenums and an HVAC fan. The thermostat selectively controls the HVAC system to maintain the desired temperature and resulting in a variable operating cycle period between successive on times. A fresh air intake duct is between an exterior intake vent and the return air plenum. A stale air exhaust duct is between the return air plenum and an exterior exhaust vent. The control system comprises a controllable intake damper in the fresh air intake duct and a controllable exhaust damper in the stale air exhaust duct. A controller is operatively connected to the house HVAC fan and the controllable dampers. The controller predicts an upcoming cycle period for a next successive operating cycle and calculates a fresh air vent time.

Abstract: In a multistage combustion furnace having a motor driven inducer blower and a pressure sensing device or set of switches for sensing pressure in the combustion gas flowpath through the furnace, a high firing rate blower speed and low firing rate blower speed are set based on the blower speed setting required for a medium firing rate. Each particular furnace, having its own pressures and combustion gas resistance to flow characteristics, may be provided with a database of inducer blower motor speeds required to achieve predetermined pressures in the combustion gas flowpath for a variety of combustion gas venting systems generating such resistance.

Abstract: According to one embodiment, a PMV estimating device calculates a PMV value from an average room radiation temperature, room temperature, room humidity, room air velocity, an amount of cloth worn by a person in the room, and an amount of activity of the person in the room. The PMV estimating device includes: indoor solar radiation calculator; solar radiated article temperature estimator; and average radiation temperature estimator. The indoor solar radiation calculator calculates an amount of solar radiation entered into the room. The solar radiated article temperature estimator estimates a temperature of a solar radiated article receiving the solar radiation entered into the room, by using the amount of solar radiation entered into the room calculated by the indoor solar radiation calculator. The average radiation temperature estimator estimates the average room radiation temperature by using the temperature of the solar radiated article estimated by the solar radiated article temperature estimator.

Abstract: Environmental conditions within an enclosure containing critical equipment and devices are monitored and when outside of acceptable parameters corrective action is taken to modify these environmental conditions so as to bring them within acceptable limits. Unless an environmental condition is outside of an acceptable limit, no energy expenditure is made by the environmental conditioning equipment since it does not need to be in use. When the environmental conditioning equipment is called into operation, its environmental modification influence is monitored to determine if the expected environmental modification is occurring within an expected time period(s). If the expected environmental modification does not occur within the expected time period, and/or does not occur at an expected time rate of change, then an alarm is generated to indicate that maintenance may be required for the environmental conditioning equipment.

Abstract: A method and device for automatically resetting a water-cooled air conditioner system at least once during a 24 hour period. The device included a tamper resistant housing having a micro-controller electrically coupled to a 24 volt external power source. A normally closed relay is coupled to the micro-controller, the relay having an input and output receptacle for selectively coupling to a low voltage input power line of an air conditioner system. The micro-controller is programmed to randomly open the relay input and output receptacle at least once every 24 hour period to stop the operation of the air conditioning system for timed sequence of about 4 minutes for purposes of resetting the air conditioner system.

Abstract: A method is described for identifying faults relating to an HVAC system, such a clogged filter. Sensor data is used to estimate HVAC system efficiency. Trends in system efficiency are then used to identify faults such as clogged filters. The sensor(s) can include one or more of the following types: optical sensor, temperature sensor, pressure sensor, acoustic transducer, humidity sensor, resistive sensor, capacitive sensor, and infrared sensor. The efficiency estimation can also be based on conditions external to the building, such as data from exterior sensors and/or data gathered from third parties such as government or private weather stations. The efficiency estimation can also be based on performance metrics such as the time used to reach a set point temperature. The fault identification includes filtering out non-fault related events.

Abstract: A furnace is disclosed that includes a burner with a firing rate that is variable between a minimum and a maximum firing rate. After a call for heat is received, the firing rate is set to an initial level above the minimum firing rate, and the burner is ignited. The firing rate is then modulated downward toward the minimum firing rate. If the flame is lost during or after modulation, the burner is reignited and the firing rate is maintained above the firing rate at which the flame was lost until the current call for heat is satisfied. In some cases, the firing rate is maintained until one or more subsequent calls for heat are satisfied.

Abstract: A modulating furnace having a variable rate burner and a controller is operated at a first burner firing rate for a first period of time, and a higher burner firing rate once the first period of time has expired. In some instances, the burner may be operated only while the controller is receiving a call for heat from a thermostat or the like.

Abstract: A method for starting a combustion device, in particular after a first ignition failure, in particular for starting a gas burner under unknown basic conditions, wherein a characteristic diagram of a start air ratio depending on the burner temperature known from empirical analysis is stored for the combustion device in a memory, wherein a calibration of the starting process is performed, wherein the ratio of opening of the gas valve (w) to air volume mL necessary for ignition is iteratively determined by variation of the gas and/or air volume; and in case of ignition, the combustion device is started and the applicable air ratio (?)IGNITION is stored.

Abstract: Provided herein are embodiments of a multistage gas furnace, a controller therefor and a computer-usable medium having non-transitory computer readable instructions stored thereon for execution by a processor to perform a method for operating a gas furnace. In one embodiment, the gas furnace includes: (1) a burner, (2) a circulation fan and (3) a furnace controller. The furnace controller having: (3A) an interface configured to receive heating calls and a blower control signal, the blower control signal corresponding to an operating speed of the circulation fan and (3B) a processor configured to respond to the heating calls and the blower control signal by setting and adjusting a gas input rate for the burner that is based on the blower control signal and that corresponds to a discharge air temperature determined by a dedicated discharge air sensor associated with the furnace.

Abstract: A furnace for burning solid burning biomass fuels such a municipal waste and wood pellets including a first compartment containing a hopper, a motorized auger positioned in the bottom of the auger for conveying a solid fuel out of the hopper, a first blower tube operatively coupled to the hopper for receiving the solid fuel from the hopper and a first blower operatively coupled to the blower tube for blowing the fuel through first blower tube. In a second compartment, the furnace contains a combustion chamber operatively coupled to the blower tube opposite the first blower and a heat exchanger arranged above the combustion chamber. To cool the heat exchanger, a second blower is operatively coupled to the heat exchanger for blowing a cooling air through the heat exchanger. A programmable control system is operatively coupled to the auger, the first blower, the second blower and a plurality of thermocouples for controlling the operation of the furnace.

Abstract: A voltage application unit causes switching elements to apply voltage to flow an electric current into corresponding windings to generate a revolving magnetic field. A period derivation unit derives an energization period of the windings. A signal generation unit generates a PWM signal for causing the voltage application unit to activate and deactivate the switching elements, such that a duty ratio decreases gradually in a predetermined time period subsequent to the derived energization period. A period specifying unit specifies a detection period of an electric current, which is supplied from the switching elements presently switched and deactivated, by a predetermined time period between an edge, which is caused when the PWM signal changes in level to deactivate the switching elements, and a time point in advance of the edge in the energization period.

Abstract: The disclosure provides a controller for a multistage gas furnace, a multistage gas furnace and computer readable medium for performing a method to operate a furnace. In one embodiment, the controller includes: (1) an interface configured to receive a heating call and (2) a corrosion reducer configured to ignite the gas furnace at a high fire operation based on if an indoor circulating fan of the gas furnace is active.

Abstract: A controller for a variable heating system is operable to control a stepper motor operated gas valve to adjust gas flow to vary the heating level. The controller includes a first terminal for receiving a thermostat signal requesting heating, an electronic memory, and a microprocessor in communication with the electronic memory and first terminal. The microprocessor detects a thermostat signal requesting heating, and generates a control signal for the stepper motor to operate the gas valve. The microprocessor includes a programmable read-only-memory encoded with an instruction to store a time duration during which the microprocessor detects a thermostat signal requesting heating, and further encoded with an instruction operable to determine a predetermined heating level based on the stored time duration. The microprocessor responds to a thermostat signal requesting heating by determining the number of steps the motor must move to vary the gas flow corresponding to the predetermined heating level.

Abstract: The present invention relates to a control method of preventing backflow of exhaust gas into combustion chambers of boilers or water heaters that are not in operation for a multiboiler comprising a plurality of boilers or water heaters connected in line, each of which including a wind pressure sensor measuring wind pressure of air flowing into a combustion chamber and a controller controlling a fan supplying air into the combustion chamber on the basis of the wind pressure measured by the wind pressure sensor. The control method includes measuring wind pressures using the wind pressure sensors in the operating boilers and calculating an average wind pressure, using any controller as a master controller to determine a control amount of wind of the fans of non-operational boilers based on the average wind pressure, and operating the fans of the non-operational boilers on the basis of the control amount of wind.

Abstract: A modulating furnace having a variable rate burner and a controller is operated at a first burner firing rate for a first period of time, and a higher burner firing rate once the first period of time has expired. In some instances, the burner may be operated only while the controller is receiving a call for heat from a thermostat or the like.

Abstract: A method and system for operating a modulating furnace from a single-stage thermostat. The furnace control system may include a processor, a gas valve, a variable-speed motor, and a thermostat. The furnace control may execute a thermostat algorithm comprising the steps of: determining if a heating load needs to be satisfied; running burners at an intermediate input rate, a modulated input rate, and a maximum input rate for each respective first, second, and third time intervals until the heating load is satisfied; calculating a heating load requirement as function of the time intervals; and determining an initial input rate for a next cycle based on the calculated heating load requirement.

Abstract: Methods and systems for operating a fuel fired appliance that may include an optional hardware component such as a damper are disclosed. In some cases, the presence of the optional hardware component is detected, and it is determined whether the optional hardware component is required for future operation of the fuel fired appliance. The fuel fired appliance may be operated normally if the optional hardware component is present and required, or, in some cases, if the optional hardware component is determined to be not required. If the optional hardware component is absent but required, normal operation of the fuel fired appliance may be stopped.

Abstract: Systems, methods, and controllers for controlling gas-fired appliances such as warm air furnaces are disclosed. An illustrative furnace system can include a burner unit in communication with a combustion air flow conduit and heat exchanger, a variable speed inducer fan or blower adapted to provide a flow of combustion air to the burner unit, a furnace controller and motor speed control unit adapted to regulate the speed of the inducer fan or blower, and a pneumatically modulated gas valve adapted to variably output gas pressure to the burner unit based at least in part on the combustion air flow.

Abstract: An electronic circuit for a hot water heating system conserves fuel consumption and reduces carbon dioxide emissions. A heating system includes a burner that heats water and a room thermostat. The electronic circuit comprises an override thermostat which has a setting for a lower temperature limit and an upper temperature limit below those of the room thermostat. The override thermostat is operable to activate continuous operation of the burner when the indoor temperature falls below the lower temperature limit of the override thermostat and until the upper temperature limit of the override thermostat is reached. The electronic circuit further comprises a timer operable to deactivate and reactivate the burner while the room thermostat is calling for heat.

Abstract: The present invention relates to a system and method for controlling a burner's adjustable secondary air controller. Specifically, the system relates to a control logic for the control of an air supply to a burner such as a natural gas burner used in the production and/or processing of liquid and gaseous petroleum products and in natural gas dehydration systems.

Abstract: A pellet stove utilizing gravity feed and natural draft more effectively and efficiently burns pellet fuel while producing less air pollution and ash. In one embodiment, the pellet stove has a primary combustion area comprising a burn unit removably disposed in the vent tube, a feed tube defining a fuel chamber above the burn unit and a secondary combustion area, comprising a burn box defining a secondary burn chamber, below the burn unit. The burn unit has a removable receptacle which defines a primary burn chamber that receives pellet fuel from the fuel chamber and discharges substantially burned fuel to the secondary burn chamber for additional burning. Openings in the burn box, pellet receptacle and vent tube draw air into the burn chambers. A control mechanism controls the air flow to regulate the heat generated by the pellet stove. The pellet stove can be manufactured in various aesthetically pleasing designs.