ISO 13347-3:2026

Fans — Determination of fan sound power levels under standardized laboratory conditions — Part 3: Enveloping surface methods

Scope

This document specifies a method for determining the sound power level of a fan. This document is applicable to fans as defined in ISO 13349-1. The applicability of this document is limited to the determination of airborne sound emission for the specified set-ups. Vibration is not measured, nor is the sensitivity of airborne sound emission to vibration effects determined.
The sizes of fan which can be tested in accordance with this document are limited only by the practical aspects of the test set-up. Dimensional limitations, test fan dimensions, and air performance will control the room size, power and mounting requirements for the test fan.
NOTE            Small fans can be tested according to this document or to ISO 10302-1, according to usage.
The test arrangements in this document establish the laboratory conditions necessary for a successful test. Rarely will it be possible to meet these requirements in situ and this document is not intended for field measurements.
NOTE            Intending users are reminded that, in these situations, there can be additional acoustic system effects where inlet and outlet conditions at the fan are less than ideal.
The enveloping surface methods can be used for the determination of open inlet and/or open outlet sound power level of fans for the standardized installation categories given in 4.1.
An estimation (with increased uncertainty) of ducted sound power for fans too small, or otherwise inconvenient, for testing by the in-duct method described in ISO 5136 can also be obtained by the addition of end reflection corrections (see ISO 13347-1:2025, Annex C).