1. Make sure the lining system is listed to UL 1777. Some manufacturer’s will use deceptive phrases like “tested to UL 1777” or something similar. When a lining system is listed to UL 1777, it has passed all of the tests required for a chimney lining system. Don’t take anybody’s word for this, check online yourself.
2. Make sure the installer is certified by the Chimney Safety Institute of America. Check for yourself at http://www.csia.org