EN 50216-10 describes oil-to-air heat exchangers that means a heat exchanger for the cooling of the transformer oil using a forced oil circuit and a forced air circuit.The oil-to-air heat exchangers are not included in the scope of the Pressure Equipment Directive 97/23/EC according to Article 1, § 3.12.This standard establishes essential dimensions and the requirements to ensure interchangeability and adequate mounting of the oil-to-air heat exchangers.This standard applies for dimensions and requirements of oil-to-air heat exchangers. The increase of ratings and constructional changes as well are considered in the revised standard.