The HVAC system in our house is only about 3 years old. It is still under warranty so we have it serviced on a semi-annual basis to keep it running smoothly. I am always careful to change the filter when needed and we try to maintain a constant temperature year round so that it doesn’t have to work too hard. The main problem is the fact that we opted out of a programmable thermostat when we had the system installed. Our dealer had recommended adding this feature but my wife and I felt that we were adult enough to remember to adjust the thermostat as we were leaving the house each day. Therein lies the problem, be remembering part is more difficult than we thought it would be. At first it seemed easy and we made sure we were diligent about adjusting the temperature up or down a bit while the house was vacant during the day. We thought that we had this down to a science until our energy bills started creeping up each month. We even tried leaving Post-it notes around the house so that we would remember to adjust the temperature but that didn’t seem to work either. Many days we would forget and the house would be kept warmer or cooler depending on the time of year all day long. The money that we wasted in a short six months would have easily paid for a programmable thermostat to begin with. We ended up contacting our dealer and having them come out to install the unit before a year was up. If you are ever offered this option by your AC AC dealer I highly recommend that you take them up on it, because remembering is not as easy as it sounds.