I have a 6 inch round duct that comes out of the main trunk about 5 feet from the furnace. It runs through the basement and outside the house (under the deck). What is this? The furnace also has 2" PVC vent and intake pipe, which I'm familiar with, but I've never seen this before. When the furnace or Air is on there is air flowing through this pipe. What is it? what does it do? Thanks!
It's an outside air (intake, probably, but you don't specify direction of airflow.)
Can be a simple system that forces some ventilation by bringing in fresh air all the time, can be a more complex system that alters the amount of outside air with a damper depending on the temperature inside, and outside, and called for by the thermostat (ie, so that you don't run the AC to cool off the house when you could just suck in cool air from outside the house.)
