Highly sensitive airflow direction sensing

A highly sensitive airflow sensing apparatus for indicating positive and negative pressure differentials at a flue associated with a combustion appliance located in a facility, said apparatus comprising:

• a tube for conducting an airflow stream, said tube having first and second open ends, said first open end in communication with ambient temperature air from the facility and said second open end in communication with the flue;
• a first temperature sensor providing an output signal and located adjacent to said first open end of said tube substantially out of contact with the airflow stream conducted by said tube, whereby said first temperature sensor is exposed to the ambient temperature in the facility;
• a second temperature sensor at an intermediate location in said tube and providing an output signal;
• a heat source in said tube adjacent to said second open end;
• a comparator receiving said output signals from said first and second temperature sensors, comparing said signals and providing an output indicative of comparison;
• and
• means responsive to said output from said comparator for advancing appropriate response to said output when indicative of irregular pressure differential at the flue.

A highly sensitive airflow direction sensing method comprising the steps of:

• conducting airflow in a passage between first and second volumes;
• sensing ambient temperature in said first volume;
• heating air at said passage adjacent said second volume;
• sensing temperature of said airflow being conducted in said passage;
• comparing sensed ambient temperature and sensed conducted airflow temperature;
• and
• providing an output indicative of compared ambient and conducted airflow temperatures.