I crawled around under there for a bit this weekend. I did verify that the center channel for the forced air furnace would be providing radiant heat for the underbelly. I also found a "vent" pointed down there. Directly beneath the furnace there was a nickel to quarter sized hole punched through that fabric/tarp-like barrier that opened up into some type of cavity. Surrounding the hole was metal sheeting like furnace housing itself. It looked like it was intentionally put there directly under the furnace, so I fired the furnace up and sure enough it blew air through that hole into the underbelly.
