discussed above or based upon the programmed or estimated running time of the fan in a preferred form the system is designed to allow the user to scroll through a list of available filter codes to select an appropriate code that corresponds to a particular filter number assigned to the filter in use at that time the life of the filter is automatically programmed into the system based on the manufacturer 39 s filter code once a particular selection from those available is made without use of the formula the user may also reset the counter to its default value or to restore a previous count using a combination of buttons 213 those of ordinary skill in the art will appreciate that the invention is not particularly limited in this manner once the user is finished setting the usage counter he or she may then switch the thermostat to another mode such as run mode for operation or one of the time or temperature setting modes the filter usage may also be programmed based upon a direct or indirect measurement of the actual use of the filter this may be further explained in connection with fig6 which illustrates one sample embodiment of an air handling.