There could be many reasons that your fireplace isn’t functioning correctly, and we want to help you solve the problem. Below is a list of potential issues and their respective solutions. Note that this list of problems/solutions is simplified, and a correct understanding of fireplaces requires an expert-level knowledge of airflow patterns.
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.