Hmm, I remember we had a great big exhaust fan at the top of a stairwell in the victorian monster I grew up in (holy crap, no wonder my dad drank whiskey and listened to Janis Joplin when he paid the bills). In the house I co-own now, which is two stories, 1400 s.f., the previous owner installed a sizeable skylight in the ceiling at the top of the stairs. We leave this open as a hatch for hot air, but there is no fan associated with it. We could possibly put a fan in the attic and leave the stairs pulled down as an extra air-draw, but I think the skylight working as a kind of chimney might be the best combination of effectiveness and passivity, not to mention aesthetics -- the skylight is beautiful, open or closed. I don't know. Ruediger's ruminating on it as we speak.