I am in the process of buying a home built on crawl space foundation in Michigan. I don't have any experience with crawl spaces. The house was built in 1949 and return ducts are rusted and torn. I am not sure how does the plumbing keep from freezing etc. The house has an inspection report but does not indicate as to how various things should be. I need help with a quick lesson as to what to look for and what to ask the inspector?

The first thing I would do is turn the water on to check for frozen pipes. Then I would ask that the ducts that are rusted be replaced. Check to see how long it takes hot water to reach the master bathroom. Good luck, Tom

I am guessing a certified home inspecter checked your home. Does he suggest replacing anything? Typically, in a crawlspace, the furnace is there. It keeps the pipes from freezing.
I would simply ask the inspecter "hey, what should i be asking you?"

Furnace is in the utility room so I guess, that leaves the crawl space heated by heat escaping from floor.

Ouch. Now I am wondering what is keeping the pipes from freezing. Fortunately it is as cold as the ens. Lucky you. Go in the crawlspace and see how cold it is there. Are the pipes insulated? Are there any signs of pipe repair?