ISO 13347-2:2004 gives a detailed description of reverberant room methods for the determination of fan sound power levels. It is for use under standardized laboratory conditions and recognises that tests in situ are subject to increased uncertainty. These test procedures are not necessarily appropriate to site test conditions. Acoustic system effects are presently the subject of considerable research effort.
ISO 5136, which covers the in-duct method, and ISO 10302 for small fans, should be used in conjunction with ISO 13347-2:2004.