What stainless steel liners require insulation?
For gas and oil-fired appliances, liners aren’t required to be insulated to meet warranty and installation requirements. Because of the lower flue and gas temperatures, they are less likely to catch surrounding combustible material on fire. However, even though gas and oil-fired appliances aren’t required to be insulated, they will benefit from an insulated liner. Additionally, it is safer to insulate every liner serving a wood-burning appliance.