The HVAC is in the corner. At the bottom is an air filter which then
has duct work that runs towards the water heater. Then there is a
decent sized duct that runs up, through the first floor, and into the
attic. In the attic there are two round flexible tubes connected to
this. One runs to a air intake vent in the master bedroom and another
to the hallway on the other side of the house.

The openings in the duct work are in this structure. The water heater
sits right next to it.

A picture is here linked below. Bare in mind that this is over a year
old. The basement is finished now. You can sort of see one of the
openings in the duct work at the top -- it's a white grill. The other
is a few feet below that, more slim but longer.

http://farm1.static.flickr.com/54/15...832ab758_b.jpg