What is a "Counterflow" furnace?

A "counterflow" system pulls in room air at the top of the furnace, warms the air across the combustion chamber and delivers it at the floor level. This gives an equalized floor-to-ceiling temperature. Direct-Vent Forsaire Counterflow Models include #4007732, #4007731, #6257732, #6257731, #4007332, #4007331, #5507332 and #5507331. Top-Vent Forsaire Counterflow Models include #6008532, #6008531, #3508732, #3508731, #5008732, #5008731, #6508732, #6508731, #3508332, #3508331, #5508332 and #5508331.