Heating, ventilation, and air conditioning systems require proper and regular maintenance in order to work efficiently, but even in the best case scenarios most components of such systems only last 15 to 25 years.
Furnaces on average last 15-20 years, heat pumps 16 years, and air conditioning units 10-15 years.
Tankless water heaters last more than 20 years, while an electric or gas water heater has a life expectancy of about 10 years.
Thermostats usually are replaced before the end of their 35-year lifespan due to technological improvements.
Last updated October 16 2008: 4:37 PM ET