Boiler

Every boiler has a "life time of efficient use" recommended by the manufacturer. Unless, of course, its made in China.

What nonesense. The lifetime of a boiler is decided by far too many operational and environmental factors for any manufacturer to predict a "life time of efficient use".

What is the added value of the qualification "Unless, of course, its made in China."

Is this meant to assist the OP in his question or is it just an uninformed statement to highlight your own personal prejudices.

Subaru...

One does not "calculate" the life of a boiler.

There are far too many variables.....and many types of boilers.

One of the best ways to shorten the life of a boiler is to pay no attention to the water chemistry. Another way of saying "boiler abuse" is having an MBA in charge.

Running the boiler above the MCR is another way to shorten the life.

You can make an estimate, a guess, evaluate the service life of similar boilers...

But, IMHO, you cant "calculate" a boiler's life.

What, exactly, do you mean by the word calculate ?

This cannot be calculated. Usually you get it from the manufacturers' recommendation but it comes with a whole lot of conditions some of which might be difficult to meet depending on your location and situation. eg if for some reason you fail to get the design coal as specified.