A pile should be large enough to hold heat and small enough to admit air to its center. As a rule of thumb, the minimum dimensions of a pile should be "3 feet x 3 feet x 3 feet (1 cubic yard)" to hold heat. The maximum dimension to allow air to the center of the pile is "5 feet x 5 feet x any length."
If space is a limiting factor, the pile sides should be insulated so that higher temperatures can be maintained in a much smaller volume. Smaller, commercially available units can be insulated with foam board. Piles larger than 5 feet tall and wide may need to be turned to prevent their centers from becoming anaerobic. As the material decomposes, the pile will become smaller.
Compost piles can be constructed by adding stockpiled material in batches or by placing materials in the piles as they become available. The batch method accelerates the composting process if the combined materials have the right C:N ratio and if the materials are mixed properly.