Thanks for your input.
The washer/dryer (a combo unit) is on an inside wall. It was next to an outside wall, where it was previously vented, but the room was enlarged. Now there is no room for the unit to be moved to an outside wall (since we would need to move plumbing as well and the room is built on a concrete slab).
MinEaston, I was leaning toward #2 as well, since (what Cafe Latte said) what goes up... and that's a lot of lint accumulation. Unfortunately, our ducting will not be hidden in a crawlspace since the contractor finished those walls before he decided to look a few steps ahead...
Also, MinEaston, does your dryer seem to take care of the lint problem through the in-unit filter, or did you install some sort of filter near the elbows, or just clean out the ducting regularly?
Can't you just eat what I put in front of you? Do you have to know what it is?
Ria Parkinson, Butterflies (BBC, 1978-83)