A plumber with heating experience should be able to give you good advise.
I prefer a heating guy with plumbing experience to do my work.
Ask the guy doing your work these questions and if he can not give you a clear answer, show him this forum and think about who you have hired.
If he is any good he will be able to answer any questions you have.
You do not necessarily have to understand all the concepts discussed here, just enough knowledge to ask the right questions of the people you hire.
It is great that you are eager to learn new things, just remember it is a never ending process and it takes some work on your part.
The old adage 'Give a man a fish, feed him for a day but teach him how to fish and you feed him for a lifetime' comes to mind.
Here is a good link to chimneyshttp://inspectapedia.com/chimneys/aschim01.htm
Google is you friend.