A. If you use a 5 degree setback you can save between 5-10% on your annual cost to run the furnace.  The cost to install a programmable varies greatly depending on what you purchase. It may take between 5-10 years or more to get a full payback. 

A. Gas or Oil Furnaces are rated in AFUE (Annual Fuel Utilization Efficiency), Heat Pumps in HPSF (Heating Season Performance Factor) and Air Conditioners in SEER (Seasonal Energy Efficiency Rating). With gas furnaces you should buy a model with a 92% rating if you run the blower continuously for better air filtration as it has a more efficient blower. However, if you allow the air to turn off when not heating, a 95% model will save you energy in the long run. On the A/C side it has more to do with comfort as you get to the higher SEER ratings in our climate. The base A/C is a 13 SEER for each point you go higher it uses about 10% less energy to run.