For how long are long-lasting durable goods designed to last?

It depends on the goods proven history of durability. For instance, the normal "life" of a refrigerator for home use is 15 years. Advances in technology and energy efficiency make this product more effective if one replaces it every 15 years. It will work for much longer, but it is not cost effective to work the product longer than that.

A vehicle is designed to give good value for about 100,000 traveled miles. If it is maintained well, this can be as few as 3 years or as long as 12 years.

A home is usually the most permanent "durable goods" product. Structurally, this product will last over 200 years, given proper maintenance. But we all know of homes which are less than 30 years old that are uninhabitable.

For the most satisfaction in purchasing such goods, it pays to do the research to determine the length of time the product is supposed to work and which brands of the product actually deliver on the promise.