Furnace combustion gas sensing and control systems and methods
Patent Information
- Application Number
- US19/092667
- Authority / Receiving Office
- US · United States
- Patent Type
- Applications(United States)
- Current Assignee / Owner
- Filing Date
- 2025-03-27
- Publication Date
- 2026-10-01
Smart Images
Figure US20260298468A1-D00000_ABST
Abstract
Description
BACKGROUND
[0001] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
[0002] Modern residential and industrial customers expect indoor spaces to be climate controlled. In general, heating, ventilation, and air conditioning (“HVAC”) systems circulate an indoor space's air over low-temperature (for cooling) or high-temperature (for heating) sources, thereby adjusting the indoor space's ambient air temperature. Some HVAC systems generate these low-and high-temperature sources by, among other techniques, taking advantage of a well-known physical principle: a fluid transitioning from gas to liquid releases heat, while a fluid transitioning from liquid to gas absorbs heat. In an HVAC system having a heat pump or air conditioner, for instance, a fluid refrigerant can circulate through a closed loop of tubing that uses a compressor and other flow-control devices to manipulate the refrigerant's flow and pressure, causing the refrigerant to cycle between the liquid and gas phases. Generally, such phase transitions occur within heat exchangers, which are part of the closed loop and designed to transfer heat between the circulating refrigerant and flowing ambient air.
[0003] Although a circulated refrigerant can be used in this manner to heat indoor spaces, HVAC systems can also or instead have a furnace for heating indoor spaces. Many furnaces provide heat to indoor spaces through combustion of a fuel, such as natural gas or propane. These furnaces often have a heat exchanger that is heated by fuel combustion and that transfers heat to ambient air flowing through the furnace past the heat exchanger. A separate flow of exhaust gas from the fuel combustion can be routed out from the furnace, such as through a flue pipe.SUMMARY
[0004] Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
[0005] Some embodiments of the present disclosure generally relate to a furnace having a gas sensor for analyzing combustion gas produced by burning a fuel within the furnace. In some instances, the gas sensor is a carbon monoxide sensor for detecting carbon monoxide in the combustion gas. The furnace of some embodiments includes a sampling circuit that routes a portion of the combustion gas from a vent conduit, such as a flue pipe, to the gas sensor for analysis. The furnace includes a control board configured to control operation of the furnace. This control may include taking mitigation action, such as stopping combustion in the furnace, if an amount of carbon monoxide or some other combustion byproduct detected with the gas sensor exceeds a threshold level.
[0006] Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS
[0007] These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
[0008] FIG. 1 illustrates an HVAC system with a furnace for heating indoor spaces within a structure in accordance with one embodiment of the present disclosure;
[0009] FIG. 2 depicts components of the furnace of FIG. 1, including a heat exchanger, a furnace control board, and sensors, in accordance with one embodiment;
[0010] FIG. 3 illustrates flow of combustion gas in the furnace of FIGS. 1 and 2 during operation, including flow of a combustion gas sample through a sampling circuit, in accordance with one embodiment;
[0011] FIG. 4 is a perspective view of a furnace having a sampling circuit for analyzing combustion gas in accordance with one embodiment; and
[0012] FIG. 5 is a partial front elevational view of the furnace of FIG. 4 in accordance with one embodiment.DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0013] Specific embodiments of the present disclosure are described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers'specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
[0014] When introducing elements of various embodiments, the articles “a,”“an,”“the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
[0015] By way of example, and turning now to the figures, FIG. 1 illustrates an HVAC system 10 in accordance with one embodiment. As depicted, the system 10 provides heating for a residential structure 12. But the concepts disclosed herein are applicable to a myriad of heating situations, including industrial and commercial settings. And while some HVAC systems provide each of heating, ventilation, and air conditioning, others do not. The term “HVAC system,” as used herein, means a system that provides one or more of heating, ventilation, air conditioning, or refrigeration. For example, a furnace that does not provide cooling or ventilation, and an air conditioner that does not provide heating or ventilation, are considered HVAC systems. The use of the term “HVAC” in describing a system, unit, component, equipment, etc., herein is not to be interpreted as a requirement that each of heating, ventilation, and air conditioning is provided.
[0016] As depicted in FIG. 1, the HVAC system 10 includes a furnace 16 to provide heated air to indoor spaces 14. The furnace 16 combusts fuel to produce heat. In some embodiments, the furnace 16 is a gas furnace that combusts natural gas to produce heat. In some other embodiments, however, the furnace 16 could combust propane, heating oil, or another suitable fuel to provide heating. In addition to the furnace 16, the HVAC system 10 can also include other equipment, such as an air conditioner or heat pump in some instances if cooling is also desired for the indoor spaces 14.
[0017] Ambient air of the structure 12 can be routed through the furnace 16 to heat the air. Many North American residences, as well as some commercial and industrial buildings, employ “ducted” systems, in which a structure's ambient air is circulated over a central indoor heat exchanger and then routed back through relatively large ducts (or ductwork) to one or more climate-controlled indoor spaces. In FIG. 1, the HVAC system 10 includes one or more ducts or ductwork 18 to route air that is to be heated to the furnace 16. In at least some instances, this air is heated by passing the air over one or more heating elements (e.g., furnace tubes), and the heated air is provided to the indoor spaces 14 through one or more ducts or ductwork 20. The ducts or ductwork 18 and 20 can include relatively large pipes, which may be rigid or flexible. The ductwork may also include other equipment, such as dampers and plenums, to facilitate flow of air through the HVAC system 10.
[0018] As is well known, the HVAC system 10 may be in communication with a thermostat 22 that senses the indoor space's temperature and allows the structure occupants to “set” the desired temperature for that sensed indoor space. The thermostat may operate using a simple on / off protocol that sends 24V signals, for example, to the HVAC system 10 to either activate or deactivate various components, or it may be a more complex thermostat that uses a “communicating protocol,” such as ClimateTalk or a proprietary protocol, that sends and receives data signals and can provide more complex operating instructions to the HVAC system.
[0019] Additional details regarding operation of the furnace 16 may be better understood with reference to FIGS. 2 and 3. As depicted in FIG. 2, for instance, the furnace 16 includes a blower 30 and a heat exchanger 32. The blower 30 provides the motivational force to generate airflow and circulate ambient air through the furnace 16 and ductwork 18 and 20. The blower 30 of some embodiments includes a blower wheel driven by a blower motor to generate airflow, but the blower 30 and its components can be provided in any suitable form. The blower 30 can be a variable speed blower, a multi-speed blower (e.g., a two-speed or three-speed blower), or a single-speed blower.
[0020] The blower 30 of FIG. 2 pushes air 34 past one or more heating elements (e.g., heat exchanger tubes 72 of FIG. 3) of the heat exchanger 32. The flowing air absorbs heat from the heating elements and exits the heat exchanger 32 as heated air 36, which may then be provided to an indoor space 14 as described above. While the blower 30 is positioned in FIG. 2 to push air 34 into the heat exchanger 32, in some other instances the blower 30 could be positioned downstream of the heat exchanger 32 to draw the air 34 through the heat exchanger 32 and into the blower 30.
[0021] The furnace 16 also includes one or more burners 40 for generating heat used to warm the ambient air flowing through the heat exchanger 32. The burners 40 are inshot burners in at least some instances, but other burners (e.g., upshot burners, conversion burners, or ribbon burners) could also or instead be used. The burners 40 can combine air with fuel for combustion to generate heat. The fuel may be ignited with a hot surface ignitor, a direct spark ignitor, a pilot light, or in some other manner. The burning of the fuel via the burners 40 heats the heat exchanger 32, which may be used to heat air flowing through the furnace 16 to the indoor spaces 14. The furnace 16 of FIG. 2 also includes a fuel supply valve 42 for controlling flow of fuel 44 (e.g., natural gas) to the burners 40.
[0022] In addition to generating heat, burning the fuel 44 in the burners 40 produces combustion gas. The combustion gas generally includes various gaseous components, such as nitrogen, carbon dioxide, and water vapor. In some instances, the combustion gas may also include one or more other gaseous components, such as carbon monoxide, nitrogen oxides, and sulfur oxides. The combustion gas may be routed out of the furnace 16 in any suitable manner. In at least some embodiments, an inducer blower 50 of the furnace 16 draws the combustion gas through the heat exchanger 32 (e.g., through the heat exchanger tubes 72) and expels the combustion gas as exhaust, which is generally represented by arrow 52 in FIG. 2. The combustion gas expelled by the inducer blower 50 may also be described as exhaust gas or flue gas.
[0023] The depicted furnace 16 also includes a main controller, such as a main control board 60, and one or more sensors 62. The main control board 60 (e.g., a furnace control board) controls operation of various other components of the furnace 16, such as the blower 30, the burners 40, the fuel valve 42, and the inducer blower 50. For instance, the control board 60 may issue component commands to control ignition and combustion of the fuel 44, to control operation of the blower 30 to move air through the furnace 16, and to control operation of the inducer blower 50 to expel combustion gas from the furnace 16. The control board 60 may receive signals from the thermostat 22 and the one or more sensors 62. Various sensors 62 may be included in the furnace 16, such as a high limit switch, a flame rollout switch, or a flame sensor, to name just several examples. And as discussed in further detail below, in at least some embodiments the one or more sensors 62 include a gas sensor 80 (FIG. 3) for sensing a combustion byproduct (e.g., carbon monoxide) from burning of the fuel 44.
[0024] The control board 60 can take any suitable form but is provided as a printed circuit board in at least some embodiments. The control board 60 is shown in FIG. 2 as having a processor 64 (e.g., a microprocessor or microcontroller), a memory 66, and input / output devices 68 (e.g., wire terminals and communications circuitry). In at least some embodiments, the memory 66 (e.g., an electrically erasable programmable read-only memory) stores instructions executed by the processor 64 of the board to facilitate monitoring or control of HVAC components, such as other components of the furnace 16. For instance, the control board 60 may control operation of the blower 30 by sending command signals from the control board 60 to a motor controller of the blower 30 to control the motor of the blower. The control board 60 also controls combustion heating, such as by sending commands for controlling supply of natural gas or another fuel (e.g., via the fuel valve 42), controlling ignition of the fuel, and controlling the inducer blower 50 to create a draft of combustion gas through the heat exchanger 32. The control board 60 may also monitor operating parameters of the HVAC system 10, such as temperature, airflow, and pressure, and may receive input signals from the one or more sensors 62.
[0025] The control board 60 can communicate with other components via the input / output devices 68. The control board 60, for example, may be connected to the blower 30 (e.g., to a motor controller of the blower 30), the inducer blower 50 (e.g., to a motor controller of the inducer blower 50), the fuel valve 42, the burners 40, an igniter, and one or more sensors 62 (which may include the gas sensor 80 of FIG. 3) with wires connected at terminals of the control board 60. The control board 60 may also be connected to receive signals from other devices, such as the thermostat 22. The various components in communication with the control board 60 may communicate over wired connections in some embodiments, although wireless communication with the control board 60 could also or instead be used.
[0026] As noted above, the furnace 16 can include a gas sensor 80 for sensing a combustion byproduct from burning of the fuel 44. The gas sensor 80 could be installed in any suitable location and manner in the furnace 16. In some instances, however, the gas sensor 80 is installed in a sampling loop or circuit, an example of which is shown in diagram 70 of FIG. 3. In this depicted embodiment, the inducer blower 50 operates to draw combustion gas 74 (from the burning of the fuel 44) through one or more heat exchanger tubes 72 of the heat exchanger 32 and expels this gas as exhaust gas 76 (which is generally represented by arrow 52 in FIG. 2). The exhaust gas 76 may generally be routed out of the furnace 16, such as through a flue vent conduit. But as shown in FIG. 3, at least a portion of the exhaust gas 76 is routed (as represented by arrow 78) to the gas sensor 80 for analysis in some embodiments. This sample portion may be referred to as a sample exhaust gas stream or a sample flue gas stream. The sampled portion analyzed by the gas sensor 80 may be returned to the inducer blower 50 in some cases, such as represented by arrow 82 in FIG. 3. More specifically, in some embodiments the sample exhaust gas stream flows from the gas sensor 80 to a low-pressure side (i.e., an inlet) of the inducer blower 50, and a pressure differential between the inlet (low-pressure) side and outlet (high-pressure) side of the inducer blower 50 during operation causes the inducer blower 50 to draw the sample exhaust gas stream through the sampling loop.
[0027] The gas sensor 80 includes a carbon monoxide sensor in at least some embodiments but may also or instead include one or more of a nitrogen oxide sensor, a sulfur oxide sensor, or a sensor for detecting some other gas in the sampled portion. The gas sensor 80 can include an electrochemical sensor, a semiconductor sensor, an optical sensor, or some other sensor type to detect a gas of interest (e.g., carbon monoxide, a nitrogen oxide, or a sulfur oxide) in the sampled portion. In addition to a sensing element to detect gas of interest, it will be appreciated that the gas sensor 80 may include circuitry within a sensor housing to facilitate gas sensing and communication with the control board 60. This circuitry may include a processor (e.g., a microprocessor or microcontroller), a memory (e.g., an electrically erasable programmable read-only memory), and input / output devices (e.g., a wire terminal and communications circuitry). In some embodiments, for instance, the gas sensor 80 includes a memory encoded with instructions executed by a processor of the gas sensor 80 to receive and process a sensing element output to determine the presence or an amount of a gas of interest in the sample exhaust gas stream and to communicate with the control board 60. In some other cases, this functionality may be hardwired in integrated circuits of the gas sensor 80 rather than being implemented via executable instructions. Some gas sensors 80 may be used to determine whether an amount of a gas component in the sample exhaust gas stream exceeds a predetermined threshold level. In the case of a carbon monoxide sensor 80, for example, the sensor 80 may be used to determine whether carbon monoxide is in the sample exhaust gas stream in an amount exceeding a predetermined threshold level for carbon monoxide, such as 50 parts per million (ppm), 100 ppm, 200 ppm, 300 ppm, or 400 ppm. As discussed in additional detail below, the control board 60 may initiate one or more mitigation actions, such as ceasing combustion, if the gas component measured with the sensor 80 exceeds the threshold level.
[0028] The furnace 16 can take any suitable form, an example of which is depicted in FIGS. 4 and 5 in accordance with one embodiment. In this depicted embodiment, the furnace 16 includes a cabinet or housing 102 having portions 104 and 106 for receiving other components of the furnace 16. The burners 40, the fuel valve 42, the inducer blower 50, and the heat exchanger 32 are shown within the portion 106. The blower 30 (FIG. 2) is installed in the portion 104 to direct air across heat exchanger tubes 72 of the heat exchanger 32. The control board 30 (FIG. 2) is also installed in the portion 104. The furnace 16 can include one or more removable covers or panels 108 to facilitate access to components within the housing 102. An example of such a panel 108 on a front side of the portion 104 of the housing 102 is depicted in FIG. 4. Although omitted from FIG. 4 to show certain components within the portion 106 of the housing 102, the front side of the portion 106 may include a similar removable panel 108.
[0029] As depicted in FIG. 4, the furnace 16 includes a manifold 112 for directing fuel from the fuel valve 42 to burners 40 installed in a burner box 114. The fuel valve 42 has a fuel supply inlet 116 for receiving the fuel 44, such as natural gas routed into the furnace 16 through a supply conduit connected to the inlet 116. During heating, the fuel valve 42 is opened to supply the burners 40 with fuel 44, which may be mixed with air and ignited to generate heat through combustion. Although shown in FIG. 4 as having three burners 40 and three heat exchanger tubes 72, the furnace 16 may have any suitable numbers of burners 40 and heat exchanger tubes 72. The inducer blower 50 is activated to draw the resulting combustion gas from the burners 40 through the heat exchanger tubes 72 into a collector box 118, from the collector box 118 to the inducer blower 50, and then out from the inducer blower 50 as exhaust into a flue vent conduit 122 connected to an outlet 124 of the housing 102. Operation of the inducer blower 50 also draws air into the housing 102 through an air intake 126 and to the burners 40 to aid fuel combustion. Air may enter the furnace 16 through the air intake 126 via an air intake pipe 132 (FIG. 5). An external vent pipe 136 (FIG. 5) may be connected to the outlet 124 to route exhaust flowing out of the housing 102.
[0030] A partial front elevational view of the furnace 16 is depicted in FIG. 5 with the burners 40, the fuel valve 42, and the manifold 112 omitted to better depict certain features, such as inlet openings 134 for the heat exchanger 32 and a flue gas sampling circuit 140 for analyzing gas from the flue vent conduit 122. The burners 40 may be positioned at the inlet openings 134 so that combustion gas from burning the fuel 44 flows into the heat exchanger tubes 72. The flue gas sampling circuit 140 may be used to route a sample of flue gas to the gas sensor 80 for analysis, such as described above.
[0031] In some instances, the flue gas sampling circuit 140 is also used to condition the sample of flue gas to facilitate analysis by the gas sensor 80. As depicted in FIG. 5, for example, the flue gas sampling circuit 140 includes a conduit 142 for routing a sampled portion of the flue gas from flue vent conduit 122 to a heat exchanger 144 for conditioning. The heat exchanger 144 is shown as a cooling coil in FIG. 5 but could be provided in some other form (e.g., a finned heat sink) suitable for dissipating heat from the sampled flue gas. In some embodiments, the heat exchanger 144 is made of stainless steel or another metal to facilitate heat transfer and cooling of the sampled portion of the flue gas, but other thermally conductive materials may also or instead be used. The heat exchanger 144 may be positioned at any suitable location. In at least some embodiments, the heat exchanger 144 is positioned in the air intake pipe 132, in the air intake 126, or in front of the air intake 126 so that the air flowing into the furnace 16 to facilitate combustion (i.e., the combustion airflow) is directed across the heat exchanger 144. This combustion airflow has a temperature that may be significantly lower than that of the flue gas and cools the sampled flue gas passing through the heat exchanger 144. Cooling of the sampled flue gas in the heat exchanger 144 can result in condensation of water within the heat exchanger 144. The flue gas sampling circuit 140 of FIG. 5 includes a conduit 146 that serves as a drain line to route this condensate water from the heat exchanger 144 to the collector box 118. In one embodiment, the heat exchanger 144 conditions the sampled flue gas so that the flue gas analyzed by the gas sensor 80 has a temperature of no more than 200° F. and a relative humidity of no more than eighty percent.
[0032] Sampled flue gas conditioned by the heat exchanger 144 may flow to the gas sensor 80 of the sampling circuit 140 through a conduit 148. In some embodiments, including that shown in FIG. 5, the conduits 146 and 148 are connected in fluid communication with the heat exchanger 144 via a fitting at the outlet of the heat exchanger 144. The sampled flue gas routed through conduit 148 to the gas sensor 80 may be analyzed for one or more gaseous components (e.g., carbon monoxide), such as described herein. The sampling circuit 140 also includes a conduit 150 that connects the gas sensor 80 in fluid communication with the low-pressure side of the inducer blower 50. When operated, the inducer blower 50 causes the pressure in the vent conduit 122 at the inlet of the sampling circuit 140 to be higher than the pressure at an outlet of the sampling circuit 140 (e.g., the end of conduit 150 at the inducer blower 50); this pressure differential draws the sampled flue gas into the sampling circuit 140 from the vent conduit 122 and through the sampling circuit to facilitate analysis with the gas sensor 80. The conduits 142, 146, 148, and 150 are stainless steel piping in at least one embodiment. But any or all of these conduits may also or instead be made with other materials, examples of which include another metal (e.g., copper), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), rubber, fluoropolymer, or some other polymer.
[0033] The control board 60 of some embodiments is configured to receive a signal from the gas sensor 80 and to selectively initiate mitigation actions (e.g., disabling combustion) if a level of a gas component (e.g., carbon monoxide) detected with the sensor 80 exceeds a threshold level. The comparison of the level of the sensed gas component to the threshold level may be performed by the sensor 80 itself or by another component, such as the control board 60. For instance, the comparison may be performed by the sensor 80, which can then transmit an electronic signal to the control board 60 to indicate that an amount of the gas component measured with the sensor 80 exceeds the threshold level. In other cases, the sensor 80 may transmit a signal representative of the amount of the gas component sensed and the comparison can be done by the control board 60. The control board 60 is programmed or otherwise configured to initiate one or more mitigation actions based on the detected gas component level, such as if the measured gas component level exceeds a threshold level. This may include automatically entering the furnace 16 into a shutdown mode in response to the amount of carbon monoxide (or other gas component) measured with the gas sensor 80 exceeding a threshold level. For instance, the control board 60 may stop fuel combustion in the furnace 16 (e.g., by closing fuel valve 42). The control board 60 may also keep the inducer blower 50 running after ceasing combustion to further vent the combustion gas from the furnace 16. The inducer blower 50 may be kept running after combustion for a predetermined time duration, such as two minutes, or until the level of the gas component detected with the sensor 80 falls to a predetermined level. The control board 60 may enter a lockout mode following detection of carbon monoxide or other gas component exceeding a threshold level to prevent combustion heating in the furnace 16, such as until the level of the gas component falls to an acceptable level or until the furnace 16 can be serviced. And in some cases, data related to sensed gas component levels and mitigation actions taken is communicated to a user or saved for future reference (e.g., by a technician). The control board 60 may store an event log in memory, for example.
[0034] While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
Claims
1. An HVAC system comprising:a furnace including:a heat exchanger installed within a furnace housing;a burner positioned within the furnace housing to provide heat to the heat exchanger through combustion of a fuel;a fuel valve connected to provide the fuel to the burner;an inducer blower positioned in the furnace housing to draw combustion gas from the burner through the heat exchanger;a vent conduit connected to receive the combustion gas from the inducer blower; anda carbon monoxide sensor positioned within the furnace housing to detect carbon monoxide produced from the combustion of the fuel.
2. The HVAC system of claim 1, wherein the carbon monoxide sensor is in fluid communication with the vent conduit so as to allow a portion of the combustion gas to flow from the vent conduit to the carbon monoxide sensor.
3. The HVAC system of claim 2, comprising a cooling coil installed in fluid communication between the vent conduit and the carbon monoxide sensor to cool the portion of the combustion gas that flows from the vent conduit to the carbon monoxide sensor.
4. The HVAC system of claim 3, wherein the furnace includes an air intake that allows air for the combustion of the fuel to flow into the furnace, and the flow of this air into the furnace is directed across the cooling coil to cool the portion of the combustion gas that flows from the vent conduit to the carbon monoxide sensor.
5. The HVAC system of claim 3, comprising a conduit connecting the cooling coil to the carbon monoxide sensor.
6. The HVAC system of claim 5, comprising a collector box positioned in the furnace housing such that the combustion gas drawn from the burner through the heat exchanger flows through the collector box and to the inducer blower.
7. The HVAC system of claim 6, comprising a drain line to allow condensate water from the cooling coil to flow into the collector box.
8. The HVAC system of claim 1, comprising a furnace control board installed within the furnace housing, wherein the furnace control board is configured to receive a signal from the carbon monoxide sensor and to disable combustion within the furnace housing in the event that a carbon monoxide level detected with the carbon monoxide sensor exceeds a threshold level.
9. An HVAC system comprising:a furnace including:a burner positioned within a furnace housing and configured to generate heat through fuel combustion;a flue vent conduit positioned within the furnace housing; anda flue gas sampling circuit positioned to receive a sample of a flue gas from the flue vent conduit, the flue gas sampling circuit including a gas sensor to analyze the sample of the flue gas and a heat exchanger positioned upstream of the gas sensor to condition the sample of the flue gas as it flows to the gas sensor.
10. The HVAC system of claim 9, wherein the furnace includes an inducer blower that supplies the flue gas into the flue vent conduit.
11. The HVAC system of claim 10, wherein the inducer blower is in fluid communication with the flue gas sampling circuit such that the inducer blower draws the sample of the flue gas into the flue gas sampling circuit from the flue vent conduit.
12. The HVAC system of claim 9, wherein the heat exchanger of the flue gas sampling circuit is a cooling coil.
13. The HVAC system of claim 12, wherein the cooling coil is an air-cooled cooling coil positioned between an air intake of the furnace housing and the burner to allow air flowing to the burner from the air intake to dissipate heat from the air-cooled cooling coil.
14. The HVAC system of claim 9, wherein the gas sensor includes a carbon monoxide sensor.
15. A method comprising:using an inducer blower to induce flow of combustion gas through a heat exchanger within a furnace such that the combustion gas flows into an inlet side of the inducer blower and is expelled through an outlet side of the inducer blower into an exhaust conduit;using the inducer blower to also induce flow of a portion of the combustion gas out from the exhaust conduit into a sampling circuit having a carbon monoxide sensor; andanalyzing the portion of the combustion gas using the carbon monoxide sensor.
16. The method of claim 15, wherein analyzing the portion of the combustion gas includes measuring carbon monoxide in the portion of the combustion gas.
17. The method of claim 16, comprising comparing the amount of measured carbon monoxide in the portion of the combustion gas to a threshold level.
18. The method of claim 17, comprising transmitting an electronic signal to a furnace control board of the furnace to indicate that the amount of measured carbon monoxide in the portion of the combustion gas exceeds the threshold level.
19. The method of claim 17, comprising automatically entering the furnace into a shutdown mode in response to the amount of measured carbon monoxide in the portion of the combustion gas exceeding the threshold level.
20. The method of claim 19, wherein automatically entering the furnace into the shutdown mode includes stopping fuel combustion within the furnace and using the inducer blower after stopping fuel combustion to route remaining combustion gas from the furnace.