Mike, one of my inspectors had the same problem. Some people are poor test takers. You have to learn to read and interpret the questions and find the BEST answer. I just took it myself just to experience it. I would review the heating systems you are not familiar with, including graphics that you can find on them, if you can not see one in action. Carson Dunlop has some books that are used as reference. You can also check the NAHIE website for more references.