Carbon monoxide is an invisible, unscented and at high levels can be a deadly gas. Lower concentrations of carbon monoxide can cause headaches, lightheadedness and fatigue. Winter months may pose health and safety risks with heating systems. Poorly maintained chimneys and flues may release carbon monoxide and other harmful gases into the air.
Have your furnace thoroughly inspected by a certified technician before your turn on your heat. Ignoring signs of carbon monoxide can be deadly. All flue pipes should be properly sealed and make sure your hvac technician checks carefully the heat exchanger in the furnace. Also as a side note you want to place all carbon monoxide detectors closest to the ground, as this gas always rises and you want to have one alarm per level.