
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