In order for a forced air furnace system to properly and effectively distribute heated air throughout the house, return air ducts with vents must be in place. However, the return air vent in this picture is located right next to the gas-fired furnace. If the furnace or chimney flue for the furnace ever malfunctioned and pushed carbon monoxide (CO) back into the basement, the return air vent could draw the CO into the supply air and distribute it throughout the house creating a potentially deadly situation. This vent will need to be removed and the opening sealed. Return air vent openings need to be located no less than 10 feet away from fossil fueled fired furnaces or water heaters.