No matter how you look at it, the worst place to get a supply of air to be heated is off the floor of the basement. It's the coldest air in the house.
All furnaces that are properly installed have cold air returns from the heated rooms, returning cool air from the living space to be reheated. If modern furnaces did not have the closed-loop system, they would lose ~half their efficiency.
Unless you want to heat your basement with air that should be heating your upstairs, then hook up some form of positive airduct from your cold air return to the fan inlets, and the openings on the 'bonnet' over the sides of the Hyfire.
WNY reported about a 1/3 savings in coal use, and an increase in temperatures upstairs from a max of about 62* to a comfortable 72*.. proof that this works.. heating warm air to hot is better than heating cold air to warm..
Give it a try, a bit of ductwork and head scratching will get it done, and you then can tell us how well it worked..