Thanks, Timothy's userful links.
After I read the first link, I think I have a general idea what should I do except for the ventilation pipe in the attic. In my house, those pipe in the attic is flexible one, not metal one.
Do you think I'd better change those flexible one into metal one and then insulate them?
Thanks for Waterloo's comments, too.
1. I will try to find some contactor for it. Do you have any good contractor be worthy of recommend to me?
2. I don't agree it. I trusted the home inspector very much and paid the money for his experience to help us. Then I made the final purchase offer on the house based on his inspect result.
However, because he made wrong analysis or ignore some, I purchased a big trouble with so many money. Is it fair? If he did not do anything for his big mistake, I will ask for some legal protection or I can report it to his registered association. (*sigh* No one would like do it, if they got some fair treatment).
???
Finally, could anyone recommend some contractor for upgrading the ventilation system? Thanks in advance...