An apparatus and method for heat treating a plurality of glass substrates. The glass substrates are supported on support platform and housed in a heat treating furnace. The substrates are supported in a substantially vertical orientation by restraining pins extending through walls of the furnace, and are separated from each other by frame-shaped spacing members. The spacing members reduce convection currents between the substrates and reduce or eliminate the post-heat treating distortion of each glass substrate to less than 100 μm over the entire surface of the substrate.