If you have a gas furnace it is a good idea to check to see if the flexible gas line is protected. Often on older homes, the flexible gas line that passes through the furnace cabinet is not protected, which can cause damage to the line by vibration caused by the bower fan. If the gas line is compromised or a cut develops, a gas leak can occur. In some cases structure and even explosions have been known to occur. This gas line can be protected by installing a sleeve of pipe insulation at the point where the pipe passes through the furnace housing. However, the best solution is to have an HVAC contractor install a ridged pipe extension.