Experts are recommending families check their furnaces before turning them on. A recent check of a North Little Rock furnace by Advantage Service Company showed a positive reading for Carbon Monoxide. Carbon Monoxide is an odorless, colorless gas that can be fatal when inhaled. Technicians tell News 4 Arkansas they`ve seen furnaces that haven`t been checked in at least 7 years. Experts recommend having your furnace professionally checked at least once a year and installing a carbon monoxide detector in your home.