Help understanding Allegro Furnace Operation

Doug, the area in that hole is pretty well sealed up in the basement. My guess is that most of the "cold air" is returned from that large heat outlet which also sits down in that hole, basically recirculating much of the heated air back through the unit. I guess the only thing I can do is to purchase a floor register to put back over the hole. I noticed a style of grate which has a built in diverter that is made to travel beneath a piece of furniture, kind of a snorkel looking thing.

Basement heat, none found. I ran both furnaces and was unable to find any type of heat supply for the basement.