Consumer Reports and other industry publications say that the average life of heating and cooling equipment is 12-15 years. It is not that at 15 years your system will quit working or that you may not have 20 years of worry free trouble, but at 12-15 years the equipment has given many years of service and may become more prone to costly repairs. Also, a major factor is that the equipment efficiency is always improving. Just 10 years ago most furnaces were 80% efficient and now most are near 95%. So just by replacing a 10 year old furnace, depending on efficiency, you could reduce your heating cost by 15%. For central air conditioning, the federal goverment regulates the minimum efficiency which is SEER (seasonal energy efficiency ratio). Just like a vehicle's MPG, the higher the number, the better. In 2006, the minimum went from 10 to 13 SEER, which for Wisconsin is about $50 per year. By replacing your 10 year old air conditioner (which when it was new had an average SEER of 7 or 8) with a 13 SEER, you could cut your cooling costs in half. So even though it is only 10 years old and working ok, by upgrading you can cut your annual costs; not have to worry about costly repairs; and make your home safer and healthier.