Estimating the life expectancy of a home is about as tough as estimating the average life expectancy of a human being.

We know that American men and women are now living, on average, into their 70s. A well-built home can last for centuries, though some of its components will have to be replaced from time-to-time.

Criterium Engineers, a nationwide network of registered professional engineers who specialize in building inspections, recently published the results of a study which estimate the typical life expectancy for many common building components.

How long something lasts depends a great deal on the conditions to which it is subjected, including use, climate and temperature.

For example, a central air conditioner in a house located in the northern half of the U.S. might last fifteen years. In a southern half, where it would presumably be used year-round, it might last only 10 to 15 years. A gas/oil water heater might last 25 years in a northern U.S. house, while lasting only 15 years in a southern U.S. house.

While each home’s systems and components may last longer than these estimates, they’re useful when inspecting a home you’re thinking about purchasing.

Use these numbers as a guide and check them against the report from your home inspector. If the inspector tells you the hot water heater is 8 years old but in good condition, you might be able to assume another 5 to 8 years of usability before it needs to be replaced.

Remember, this list is no substitute for having your home professionally inspected.

Mechanical Systems
Cast iron boiler – 30 years
Steel boiler – 20 years
Hot air furnace – 20 years (northern); 10 to 20 years (southern)
Heat pump (compressor) – 10 to 15 years
Central air conditioner – 15 years (northern); 10 to 15 years (southern)
Electric water heater – 15 years
gas/oil water heater – 25 years (northern); 15 years (southern)
submersible water pump – 25 years (northern); 15 years (southern)
Non-submersible water pump – 15 years (northern); 10 years (southern);

Concrete block foundation – 50 (northern); 25-50 (southern)
Poured concrete foundation – 100 years;

Cedar/redwood – 50 years (northern); 20 years (southern)
Hardboard – 10 years (northern); 10 to 20 (southern)
plywood siding – 20 years
brick – 40 to 50 years

Fiberglass shingle – 25 years (northern); 15 years (southern)
Asphalt shingle – 20 years (northern); 10 years (southern&)
Slate – 50 years (northern); 25 years (southern)
Clay tile – 50 years (northern); 25 years (southern)
Wood shingle – 40 years (northern); 25 years (southern)
Standing seam metal – 40 to 50 years

Quality double glazed – 30 years
Average double glazed – 15 to 20 years
Average single glazed – 15 year

Hollow core doors – 20 years
Solid core doors – 40 years
Average appliances – 15 years.