Systems and methods for operating a furnace

A gas-fired furnace, comprising:

• a burner assembly configured to combust fuel and air to produce combustion gases;
• a first fan configured to circulate the combustion gases along a flow path extending through a heat exchanger of the furnace;
• a second fan configured to circulate air across an external surface of the heat exchanger to produce a conditioned airflow;
• and
• a controller configured to:
• activate the burner assembly and the first fan to combust the fuel and air and circulate the combustion gases along the flow path;
• operate the second fan to circulate the air across the external surface of the heat exchanger and produce the conditioned airflow;
• estimate an airflow rate of the conditioned airflow based on two or more parameters of a motor of the second fan, wherein at least one of the two or more parameters is indicative of a speed of the motor of the second fan and at least another of the two or more parameters is indicative of a torque of the motor of the second fan;
• deactivate the burner assembly whereby combustion of the fuel and air ceases in response to an indication by a combination of the speed and torque parameters that the estimated airflow rate is less than a minimum airflow rate;
• and
• place the furnace in an idle mode, wherein the idle mode prevents the burner assembly from operating for a predetermined period of time.

A non-transitory machine-readable medium including instructions that, when executed by a processor, cause the processor to:

• activate a burner assembly and a first fan of a furnace to combust fuel and air and circulate combustion gases along a flow path extending through a heat exchanger of the furnace;
• operate a second fan of the furnace to circulate air across an external surface of the heat exchanger of the furnace and produce a conditioned airflow;
• estimate an airflow rate of the conditioned airflow based on two or more parameters of a motor of the second fan, wherein at least one of the two or more parameters is indicative of a speed of the motor of the second fan and at least another of the two or more parameters is indicative of a torque of the motor of the second fan;
• deactivate the burner assembly, whereby combustion of the fuel and air ceases, in response to an indication by a combination of the speed and torque parameters that the estimated airflow rate is less than a minimum airflow rate;
• place the furnace in an idle mode, wherein the idle mode prevents the burner assembly from operating for a predetermined period of time.