It all depends on how well you maintain your system. Generally, both air conditioners and furnaces have a lifespan of around 15 years. Still, that period depends heavily on a variety of factors. At a certain point, it might make more sense to replace a unit that’s having trouble, rather than repair it. For instance, once your furnace reaches 10 to 12-years-old, it isn’t worth investing in a repair that costs more than half the cost of a replacement. We’ve found most furnaces and air conditioners begin to display problems around the seven to ten-year mark and require more frequent repairs. However, a brand-new unit should run smoothly and shouldn’t need repair services.