Patent ID: 8623117

Claim:
A method of monitoring a status of an air filter of an HVAC system, wherein the HVAC system has a fan for driving air through the air filter of the HVAC system, the method comprising: a) turning the fan “off” so that substantially no air is driven through the air filter; b) with the fan “off”, measuring a sensor offset differential pressure value between an upstream side of the air filter and a downstream side of the air filter; c) storing the sensor offset differential value; d) turning the fan “on” so that air is driven through the air filter; e) with the fan “on”, measuring an un-compensated differential pressure value between the upstream side of the air filter and the downstream side of the air filter; f) determining a compensated differential pressure value by removing the sensor offset differential value from the un-compensated differential pressure value; g) determining the status of the air filter based, at least in part, on the compensated differential pressure value; and h) displaying the status of the air filter on a display of an HVAC controller.