Hot air blown past memory modules under test in a heat chamber is improved. Hot air entering the chamber from an inlet pipe is split by a manifold and deflectors. Holes in the manifold allow for a relatively even air distribution within the chamber, minimizing temperature variations. Return air is collected by a heat-chamber bottom cover into a return pipe. A heating unit re-heats the return air and blows it into the inlet pipe. One side of the heat chamber is an insulated backplane. Memory modules are inserted into sockets on module motherboards, which are inserted into motherboard sockets on the backplane. On the other side of the backplane, card sockets receive pattern-generator cards outside the heat chamber but electrically connected to the module motherboards through the backplane. The pattern-generator cards exercise the memory modules. The pattern-generator cards are cooled while memory modules in the heat chamber are heated.