You can consider replacing your old furnace base on many factors.Normal lifespan of furnace is between 15 to 20 years depending on the type of the fuel (Natural Gas,Propane or Oil) and location which furnace had been initially installed. For example, a damp, moist location with little fresh air will cause the furnace heat-exchanger and mechanical parts to deteriorate faster than normal which leads to cracked heat-exchanger. Read More>>>
HVAC-R, Electrical Blog