Check out this page of the GAMA ( Gas Appliance Mfg… Association).
In the middle of the page you will find a section on “Venting Done Right”.
Download the zip files, ( one is a special for inspectors) ,which are flash player ( exe) files. Get yourself a snack and watch the BEST presentation on Venting gas appliances (My Opinion).
If you have a copy of the NFGC National Fuel gas code book, you are on top of your game!!