Dictionary.com is one of my favorite resources. Type B Gas Vent system is for use with natural gas or liquid propane category I and draft hood equipped appliances. Appliances are tested and listed to use Type B Gas Vent for a wide range of applications. This includes natural gas fireplaces, gasfired furnaces, boilers, water heaters, and wall or space heating applications. Check out the following
. link for more information http://www.elitedeals.com/duravent-type-b-vent-pipe.html.