After measuring your fireplace opening to determine the appropriate liner size, it is important that you use tools like welding equipment or gas torches with proper ventilation according to manufacturer’s directions. Before cutting any holes in inner and outer walls, be sure they are open for inspection to make sure there are no cracks which could lead carbon monoxide leaks into living areas (see below). Once work begins on either side of fireplace opening using electric saws or gas torches depending upon what materials being worked with, always wear protective clothing including gloves and safety glasses because high-temperature surfaces may result during installation process. Be aware that this type of work can release harmful chemicals such as silica dust so keep all viewers away from flue until clean up has finished afterwards; if not then breathing in this material can cause lung problems. Finally, it is critical that you install your chimney liner using high temperature caulking around all joints to prevent heat loss up the flue (see below).