We have a Navian npe-240a2. It was installed outdoors, under a long eave of about 4 ft, a few inches below it. I can see it says that using an exterior vent, 36" of space above is required. What are the concerns of an installation like this? There is not much room on this wall, and below it is a condenser, which is why it was installed high up. Should it be vented through the roof? Thank you!