Is interior fresh air venting suitable for new furnaces?
Many direct vent heaters use a through the wall concentric pipe system where the cool intake air comes in through the larger outter diameter and the hot exhaust leaves via the smaller inner diameter of the two pipes. This allows there to be a compact and safe transition through the wall so that the hot pipe does not represent a fire hazard to the surrounding wall materials. 

You should look closely at your installation to make sure that the exhaust exits are piped and vented in a safe manner without risk of high heat leading to fire danger. As you describe your installation the concentric cooling scheme is not being applied.