There is no standard single size for vacuum chambers in US vacuum ovens, because they are usually custom-designed to match the transformer class and workshop capacity. For medium power transformers in the 1-10 MVA range, typical chambers have internal diameters of about 2.5-4 meters and lengths of 4-8 meters. Larger service centers may have chambers exceeding 10 meters in length for high-voltage units. The exact dimensions are chosen based on core height, lifting clearances, and heating uniformity requirements.