Vents are listed products used for specific appliances and are not interchangeable with chimneys. They may be used only for gas or oil burning appliances.
Type B are systems usually made of metal pipe. They are made as a double wall pipe with an air space between the walls. It is used for listed gas appliances with draft hoods and should be installed only according to manufacturers instructions. The inner liner is aluminum and the outer wall is galvanized steel or stainless steel.
Type BW are listed systems shaped to permit installation in the stud cavity of a wall. They are used for gas wall appliances listed for use with type BW and may be used ONLY for that purpose. This is also a double wall pipe with an air space and has an inner liner of aluminum.
Type L are used for low temperature oil or gas burning appliances listed for use with type L. They are usually a double wall pipe with an air space between the pipe walls. Any appliance that can be vented with type B may also use a type L. It uses a stainless steel inner liner.
Single wall metal pipe unlisted may be used to vent some gas appliances since the use and installation requirements of single wall metal pipe are very restrictive. Single wall pipe is generally impractical for any appliance.