There are several signs that can tell you that your furnace is inefficient; if you notice any of these signs, contact our furnace install company for advice about a new furnace. Comparing the age of your furnace to the national average is a good starting point. The average lifespan of a furnace sold in stores today ranges from 16 to 20 years. If the furnace in your Cincinnati home is very old, contact our furnace replacement company for advice about a new furnace.