Call 911 and describe the problem. They will send the fire department out to ensure the safety of your home and will also notify the gas company. You have a gas leak in your furnace room, and it needs to be remedied immediately. The gas company will be able to determine where the leak is coming from and shut down the gas line leading to the leak. If the leak is only from the furnace, they will probably just shut off the supply to the furnace, if it is in a line that feeds the furnace they will probably shut off the gas to the whole property until repairs can be made. Responsibility for paying for the repairs also depends on where the leak is coming from.