A new combustion technology, the hot air packing (HAP) technology, was proposed and researched to improve the coal burnout and control NOx emission in down-fired boilers. Compared with the prior technology, HAP technology necessitates the addition of special secondary air ports added in the furnace ash hopper (SA-H) and the furnace bottom (SA-B). Cold-air-flow experiments in a 1:4 scale model and fluid dynamics numerical simulations were carried out to reveal the aerodynamic characteristics in a furnace with HAP technology. The experimental and simulation results coincided well with each other; and both showed that HAP technology had rational aerodynamic characteristics in the furnace. Compared with a base case, common down-fired combustion technology, HAP technology forms a larger W shape and bigger recirculation zones, as well as a larger penetration depth of primary air flow. Moreover, HAP technology destroys the dead recirculation zones and avoids air flow washing against the wall. The angle and location of SA-H have great impacts on the aerodynamic characteristics in the furnace, especially in the ash hopper. Within the six cases, the SA-H configuration with an angle of 0 degrees and the upper-located position yielded optimal results. (C) 2013 Elsevier B.V. All rights reserved.