For solid fuel appliances such as wood, pellet, or coal, chimney liner insulation is required for UL listing and should be installed using ½" Premier Wrap Insulation. For gas and oil appliances, insulation is not required for UL listing, but it is recommended for better performance. Insulating the liner can help the connected appliance operate more efficiently and can reduce condensation, especially during startup. For gas and oil applications, ¼" Premier Wrap Insulation is recommended when insulation is desired.