Arrived to our clients home over concerns that the furnace was not heating properly. He explained to me that on the extremely cold days this winter the furnace would run continuously and would never reach the 70° set point. Also his gas bills were very high. We immediately proceeded into the attic and i very quickly found the filter to be dirty as well as excessive dust accumulated in the return plenum and on the blower wheel. I showed this to our client and we discussed how dust can restrict airflow and stress system components and contribute to failure and unit not heating properly. I then proceeded to test first and second stage heat at the furnace. Everything tested fine, even with the old dirty filter. I then proceeded to the thermostat because Bill had mentioned that the outdoor unit was replaced last year. I went into the program menu of the thermostat and found that it was never set up properly for 2 stage heating. I correctly set the thermostat and explained the importance