Patent ID: 8704672

Claim:
An HVAC controller for controlling an HVAC system, the HVAC system having an air filter, the HVAC controller comprising: a controller; a memory coupled to the controller; a display coupled to the controller; wherein the controller is programmed to: receive a measured value that is related to an amount of flow restriction presented by the air filter in the HVAC system; compare the received measured value to a pre-determined threshold value stored in the memory; implement a three-level user alert system in which the controller displays on the display of the HVAC controller a first status indicator when the received measured value that is related to the amount of flow restriction presented by the air filter in the HVAC system is less than the pre-determined threshold value, a second status indicator when the measured value that is related to the amount of flow restriction presented by the air filter in the HVAC system is at least equal to the pre-determined threshold value but only for a predetermined amount of time after the measured value is detected to be at least equal to the pre-determined threshold value, and a third status indicator after the measured value that is related to the amount of flow restriction presented by the air filter in the HVAC system remains at least equal to the pre-determined value for more than the predetermined amount of time; wherein the second status indicator comprises a first text-based message comprising an explicit expression indicating that the air filter should be replaced soon; and wherein the third status indicator comprises a second text-based message comprising an explicit expression indicating that the air filter should be replaced now.