There are three main types of chimney liners.
All three types provide adequate protection, however, which liner is appropriate for your home, should be determined by a professional.
Often when having a new natural gas or propane water heater installed, a new chimney liner is recommended, or even mandated by code. This requirement is a critical safety consideration for your property and addresses several issues.
Information provided by Lindemann Chimney and Fireplace 2018