I have a high efficienct furnace which exhausts warm moist air outside the house. Next to this exhaust is the cold air intake for the furnace. On cold nights the warm moist air is sucked into the cold air intake. This warm moist air freezes inside the cold air intake clogging it up and causing the furnace to shut down. What can I do to solve this problem?

Put an elbow on the discharge pointing down and separate the two pipes by eight inches.