The life expectancy of appliances and home systems are not typically top of the mind topics for the average home owner. They are definitely relevant if you're planning to sell or buy a house, but you should take a look even if you're not planning to move. It may be more cost effective to replace some before they actually klonk out for good, considering the additional energy cost and waste caused by old/inefficient appliances. In any case, homeowners must be prepared for the "unexpected" demise of a pricey necessary item. Here's a list of items along with their typical average lifespan and an average cost to replace.

ITEM                                                    AVG. LIFE SPAN                            AVG. REPLACEMENT COST

Furnace15-20 Years$3500-$4000
Water Heater10-15 Years$800-$1000
Air Conditioner10-15 Years$5000-$5500
Toilet10 YearsUnder $500
Pipes/Plumbing75-100 Years$1200+
Dishwasher9 Years$550-$1000
Garbage Disposal12 Years$400
Oven/Range13-15 Years$1000+
Microwave9 Years$300
Electrical10 Years$1200+
Fridge13 Years$1500+
Washer and Dryer10-13 Years$1000+
Roof22-30 Years$6500+

There are many reasons to stay on top of the performance of the items listed above. The 8-10 year mark is where some appliances and home systems start their decline. If you've hit that milestone in your house, it's wise to prepare your budget to take a few hits. 

Various sources were used to collect these average numbers, but be sure to consider that each item has a broad range of bells and whistles for which you may choose to splurge. Most of the items listed require professional installation, so it's best to get a few estimates before making a decision.