prEN ISO 13350

SLOVENSKI STANDARD
01-januar-2026
Ventilatorji - Preskus lastnosti indukcijskih ventilatorjev (ISO/DIS 13350:2025)
Fans - Performance testing of jet fans (ISO/DIS 13350:2025)
Ventilatoren - Leistungsmessung von Strahlventilatoren (ISO/DIS 13350:2025)
Ventilateurs - Essai de performance des ventilateurs accélérateurs (ISO/DIS
13350:2025)
Ta slovenski standard je istoveten z: prEN ISO 13350
ICS:
23.120 Zračniki. Vetrniki. Klimatske Ventilators. Fans. Air-
naprave conditioners
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 13350
ISO/TC 117
Fans — Performance testing of jet
Secretariat: BSI
fans
Voting begins on:
Ventilateurs — Essai de performance des ventilateurs
2025-11-14
accélérateurs
Voting terminates on:
ICS: 23.120 2026-02-06
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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STANDARDS MAY ON OCCASION HAVE TO
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RIGHTS OF WHICH THEY ARE AWARE AND TO
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Reference number
ISO/DIS 13350:2025(en)
DRAFT
ISO/DIS 13350:2025(en)
International
Standard
ISO/DIS 13350
ISO/TC 117
Fans — Performance testing of
Secretariat: BSI
jet fans
Voting begins on:
Ventilateurs — Essai de performance des ventilateurs
accélérateurs
Voting terminates on:
ICS: 23.120
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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Published in Switzerland Reference number
ISO/DIS 13350:2025(en)
ii
ISO/DIS 13350:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 6
5 Characteristics to be measured . 7
6 Instrumentation and measurements . . 8
6.1 Dimension and areas .8
6.2 Rotational speed .8
6.3 Thrust .8
6.3.1 Force balance systems .8
6.3.2 Force transducers .8
6.4 Input power .8
6.5 Sound level .8
6.6 Vibration velocity .8
6.7 Volume flowrate .9
6.7.1 Instruments for the measurement of pressure .9
6.7.2 Instruments for the measurement of temperature .9
7 Determination of thrust . 9
7.1 General .9
7.2 Suspended configuration .9
7.3 Supported configuration . 12
7.4 Test procedures . 15
7.5 Test enclosure . 15
8 Determination of sound level . 17
8.1 General .17
8.2 Fan-specific sound measuring standards .18
8.3 Acoustic standards of the ISO 374X family of documents and the ISO 9614 series sound
intensity methods .18
9 Determination of vibration velocity . 19
9.1 General .19
9.2 Test arrangement .19
9.3 Test procedure .19
9.4 Acceptance vibration velocity .19
10 Determination of flowrate. 19
10.1 General .19
10.2 Upstream chamber method . 20
10.3 Upstream Pitot traverse method .21
10.4 Directly connected flowrate-measuring device .21
11 Presentation of results .23
11.1 Product description . 23
11.2 Product performance. 23
12 Tolerances and conversion rules .24
12.1 Tolerances .24
12.2 Conversion rules .24
Annex A (informative) A practical method commonly used for the determination of sound level .26
Annex B (informative) Illustration of reference sound source .29

iii
ISO/DIS 13350:2025(en)
Annex C (informative) Correction of sound pressure levels .30
Annex D (informative) Non-dimensional coefficients .31
Annex E (informative) Efficiency based on thrust measurements .33
Annex F (informative) Vertical component of thrust for jet fans with deflectors or similar
devices (where deflection angle is greater than 8 degrees) .35
Bibliography .39

iv
ISO/DIS 13350:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 117, Fans.
This third edition cancels and replaces the second edition (ISO 13350:2015) which has been technically
revised. The main changes to the previous edition are as follows:
— references to standards updated, for example ISO 5801and ISO 13349-1 and -2;
— Clause 8: Noise is preferably to be measured using the ISO 13347 series, that was developed based on
modern metrics by measuring all the way around the fan, as in the ISO 374X or ISO 9614 series. The
possibility of using these more basic noise-measuring standards is introduced in this edition of the
present standard.
— Annex A is a practical ad hoc method, where one only measures at select positions to the side of the
front of the fan. In this method, reflective surfaces are defined only near the inlet of the fan, while it
has been observed that often the sound levels measured at the outlet of the fan are higher. Because
of these shortcomings that can lead to significant errors, this annex is to be used only until the fan
noise measuring standards ISO 13347-1 to -4 (that now include category E fans) are finally approved and
published.
— Annex F, Inclusive measurement capturing the vertical component of thrust for jet fans with deflectors
or similar devices
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO/DIS 13350:2025(en)
Introduction
The need for a new edition of this document has been evident for some time. The use of the so-called jet
fan to assist in the control of quality of air in vehicle and train tunnels, as well as enclosed car parks, is an
established technology. Longitudinal methods of ventilation can show advantages in both capital cost and
running cost compared to alternative systems. Smoke and pollution control in emergency conditions can be
readily provided.
This document deals with the determination of those performance criteria essential to the correct application
of jet fans. In describing the test and rating procedures, numerous references are made to ISO 5801 as well
as to other relevant International Standards. For the determination of the noise generated by the jet fans
this standard refers to the fan noise measuring standards ISO 13347-1 to -4 that recently have been updated
to include fan category E. These standards base on the established general sound measuring standards in
the ISO 374X and ISO 9614 series.

vi
DRAFT International Standard ISO/DIS 13350:2025(en)
Fans — Performance testing of jet fans
1 Scope
This document deals with the determination of those technical characteristics needed to describe all
aspects of the performance of jet fans as defined in ISO 13349-1 and -2. It does not cover those fans designed
for ducted applications, nor those designed solely for air circulation, for example ceiling fans and table fans.
The test procedures described in this document relate to laboratory conditions. The measurement of
performance under on-site conditions is not included.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 5801, Fans — Performance testing using standardized airways
ISO 13347-1, Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
1: General overview
ISO 13347-2, Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
2: Reverberant room method
ISO 13347-3, Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
3: Enveloping surface methods
ISO 13347-4, Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
4: Sound intensity method
ISO 14694, Industrial fans — Specifications for balance quality and vibration levels
ISO 14695, Industrial fans — Method of measurement of fan vibration
ISO 13349-1, Fans — Vocabulary and definitions of categories — Part 1: Vocabulary
ISO 13349-2, Fans — Vocabulary and definitions of categories — Part 2: Categories
ISO 21940-11, Mechanical vibration — Rotor balancing — Part 11: Procedures and tolerances for rotors with
rigid behaviour
IEC 60034-2-1, Rotating electrical machines — Part 2-1: Standard methods for determining losses and efficiency
from tests (excluding machines for traction vehicles)
IEC 60034-14, Rotating electrical machines — Part 14: Mechanical vibration of certain machines with shaft
heights 56 mm and higher — Measurement, evaluation and limits of the vibration severity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13349 and ISO 5801 and the
following apply.
ISO/DIS 13350:2025(en)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
jet fan
fan used for producing a jet of air in a space and not connected to any ducting, of type E category/test
configuration
Note 1 to entry: Performance shall only be expressed as thrust and efficiency is determined from thrust measurement
or calculation. Performance characteristics relating to pressure development are not compliant.
Note 2 to entry: The air jet can be used, for example, for adding momentum to the air within a tunnel or other space
(e.g. enclosed car park), or for intensifying the heat transfer in a determined zone.
Key
a flow of air
Figure 1 — a Example of axial jet fan
Key
1 inlet
2 discharge
Figure 1 — b Example of centrifugal jet fan
3.1.1
jet fan – reference configuration (axial jet fan)
fan with 1D long silencers on inlet and outlet; no internal components within each silencer, and no accessories
fitted to either end that impact performance.

ISO/DIS 13350:2025(en)
3.2
effective fan dynamic pressure
p
d
conventional quantity representative of the dynamic component of the fan output, calculated, in the
particular case of a jet fan, from the effective fan outlet velocity and the inlet density.
Note 1 to entry: The effective fan dynamic pressure will not be the same as the average of the dynamic pressures
across the section because it excludes from consideration that part of the dynamic energy flux which is due only to
departures from uniform axial velocity distribution.
3.2.1
gross fan outlet area
A
surface plane bounded by the downstream extremity of the air-moving device
Note 1 to entry: Gross fan outlet area is, by convention, taken as the gross area in the outlet plane inside the casing or
duct or silencer (see Figure 2) without taking into account any obstructions inside the fan outlet.
3.2.2
effective fan outlet area
A
eff
outlet area with deductions for motors, fairings or other obstructions (in the particular case of a
jet fan)
Note 1 to entry: If the silencer centrebody reaches the outlet plane of the fan, then the effective fan outlet area is
defined as the annulus area at the fan outlet plane, as shown in Figure 2a).
Note 2 to entry: If the fan has a silencer without centrebody [see Figure 2b)], the effective fan outlet area will be close
to the cross- sectional area inside the silencer in order to clear any exit bellmouth form.
Note 3 to entry: If the centrebody (motor or silencer core) does not extend to the outlet plane, the effective fan outlet
area will approach the annulus area between the casing and the motor, but with some increase, as defined in Figure 2c),
for the distance between the centrebody and the outlet. Where the motor is on the upstream side, Figure 2c) is applied
to the impeller hub rather than the motor, as illustrated.
Note 4 to entry: For comparisons within the scope of research and development, alternative definitions have been
used with some success.
Figure 2 — a Gross fan outlet areas (axial type)

ISO/DIS 13350:2025(en)
AA==12x
2eff
where
1 is the height of the unit outlet;
2 is the width of the fan outlet.
Figure 2b — Gross fan outlet area (centrifugal type)
3.3
effective fan outlet velocity
v
eff
velocity calculated from thrust at standard conditions, the standard air density and the effective fan outlet area
Note 1 to entry: See 11.2.
3.4
fan outlet velocity
v
velocity calculated from the thrust at standard conditions, divided by gross fan outlet area, A
3.5.1
motor input power
P
e
electrical power supplied at the terminals of the electric motor drive
3.5.2
impeller power
P
r
mechanical power supplied to the impeller of the fan
3.5.3
fan air power
P
u
conventional power output at standard conditions; in the particular case of a jet fan, product of inlet volume
flow and effective fan dynamic pressure
3.6
impeller tip speed
v
p
peripheral speed of the impeller blade tips
3.7
thrust
T
m
fan thrust measured in accordance with this document at standard conditions

ISO/DIS 13350:2025(en)
3.8.1
thrust/impeller power ratio
r
r
thrust divided by impeller power
Note 1 to entry: The thrust/impeller power ratio is calculated as r = T /P .
r m r
3.9
fan guard
guard designed to prevent the ingestion of relatively large foreign bodies, such as drink cans, and sometimes
fitted to the inlet and outlet of jet fans
Note 1 to entry: Guards can have a marked effect on the thrust performance and noise level. Where they are specified,
measurements should be made with these guards in place.
3.10
Unit deflection devices/solutions
appurtenance designed to improve installed performance through reduction of losses in certain
circumstances.
3.11
chamber
airway in which the air velocity is small compared with that at the fan inlet or outlet
3.12
test enclosure
room, or other space protected from draught, in which the fan and test airways are situated
3.13
impeller balance grade
G grade as specified in ISO 14694
3.14
fan vibration velocity
root mean square (r.m.s.) vibration velocity over the frequency range 10 Hz to 10 kHz measured in
accordance with this document and with ISO 14695
3.15
fan impeller efficiency
η
r
fan air power divided by impeller power
3.16
fan overall efficiency
η
e
fan air power divided by motor input power
3.17
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the sound pressure radiated by the sound
source under test to the square of the reference sound pressure defined in ISO13349-1
3.18
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of the sound power radiated by the sound source under
test to the reference sound power defined in ISO13349-1

ISO/DIS 13350:2025(en)
3.19
inlet sound power level
L (in)
W
sound power level of the fan determined at the fan inlet
3.20
outlet sound power level
L (out)
W
sound power level of the fan determined at the fan outlet
3.21
total sound power level
L (tot)
W
sound power level determined for the entire fan which includes the inlet and outlet sound power levels
3.22
noise frequency range of interest
frequency range including the octave bands with centre frequencies between 63 Hz and 8 000 Hz
and the one-third octave bands with centre frequencies between 50 Hz and 10 000 Hz
4 Symbols and abbreviated terms
The following symbols and units shall apply for the parameters listed.
Abbreviated term/represented quantity Symbol SI unit
Impeller annulus area A m
a
Gross fan outlet area A m
Effective fan outlet area A m
eff
Nominal fan diameter D m
R
Length of upstream chamber side D m
Sound pressure level L dB (re 20 μPa)
p
Average sound pressure level of the measured device L dB (re 20 μPa)
p(m)
Average sound pressure level of the reference sound source L dB (re 20 μPa)
p(r)
Sound power level L dB (re 1 pW)
W
Inlet sound power level L (in) dB (re 1 pW)
W
Outlet sound power level L (out) dB (re 1 pW)
W
Total sound power level L (tot) dB (re 1 pW)
W
Sound power level of the reference sound source L dB (re 1 pW)
W(r)
Rotational speed n revolution/s
Differential pressure across a flow measuring device p Pa
Gauge pressure at the fan outlet p Pa
e2
Gauge pressure in the fan chamber p Pa
e2
Effective fan dynamic pressure p Pa
d
Volume flow q m /s
v
Impeller balance grade (ISO 14694) G μm
Motor input power P W
e
Impeller power P W
r
Fan air power P W
u
Thrust/impeller power ratio r N/W
r
Thrust/motor input power ratio r N/W
e
Non-dimensional thrust/power ratio r —
t
ISO/DIS 13350:2025(en)
Abbreviated term/represented quantity Symbol SI unit
Calculated thrust T N
c
Measured thrust T N
m
Impeller tip speed v m/s
p
Effective fan outlet velocity v m/s
eff
Fan outlet velocity v m/s
Mean throughflow velocity in a tunnel at a specified section v m/s
t
Total pressure rise Δp Pa
3 3
Standard air density 1,2 kg/m ρ kg/m
Inlet density taken as equal to the density in the test enclosure ρ kg/m
a
Fan overall efficiency η —
e
Motor efficiency η —
m
Fan impeller efficiency η —
r
Fan overall efficiency based on thrust η (T) —
e
Fan impeller efficiency based on thrust η (T) —
r
Flow coefficient φ —
Thrust coefficient Θ —
Power coefficient ϕ —
r
NOTE (T) denotes the term or quantity stated to be a function of the thrust (see Annex E). For example, η (T) is the
e
fan overall efficiency based on thrust.
5 Characteristics to be measured
5.1 General
In order that a jet fan is correctly applied and gives satisfactory performance and reliability in service, it is
necessary to determine a number of technical performance characteristics in addition to knowing the more
obvious mechanical features, such as mass, overall dimensions, and installation dimensions.
5.2 Thrust
Friction on the tunnel walls, inlet and outlet losses and sometimes traffic drag, combined with climatic
effects at tunnel portals, create a pressure drop through the tunnel. The pressure drop is matched by the
sum of the pressure increases by the jet fans due to the momentum transfer between fan discharge airflow
and airflow in the tunnel. As it is impossible to measure the momentum of the fan discharge airflow, and the
rate of change in momentum is equal and opposite to the thrust, thrust is measured instead.
5.3 Input power
In order to design the tunnel installation, it is necessary to know the input power to the fan motor. Also, this
is needed to determine the overall efficiency of the jet fan.
5.4 Sound levels
Sound levels, usually at both inlet and outlet, and, where significant, also the casing break out noise, are
established in order to ensure that the jet fan and silencer combination is optimized to match the tunnel
sound level requirements.
NOTE The fan manufacturer can only guarantee the sound power level of the fan. The sound pressure in the tunnel
will depend on the size and sound absorption characteristics of the tunnel, which are outside the fan manufacturer's
responsibility.
ISO/DIS 13350:2025(en)
5.5 Vibration velocity
For reasons of safety, reliability, and maintainability, it is essential that a realistic vibration velocity is
specified and recorded on jet fans. These shall be measured in accordance with ISO 14695.
5.6 Volume flowrate
5.7 Volume flowrate need only be measured if required for contractual reasons, which is determined with
one of the methods described in Clause 10.
NOTE It is the effective fan outlet velocity that is used to evaluate the optimum number, size, and spacing of jet
fans in a tunnel, and is calculated in accordance with 11.2
6 Instrumentation and measurements
6.1 Dimension and areas
The measurement of dimensions and the determination of areas shall be in accordance with ISO 5801:2017,
Clause 11.
6.2 Rotational speed
The rotational speed of the impeller shall be determined in accordance with ISO 5801:2017, Clause 9.
6.3 Thrust
6.3.1 Force balance systems
By the use of calibrated weights, force balance systems shall permit the determination of force or thrust
with an uncertainty of ±5 %.
6.3.2 Force transducers
After calibration by the use of calibrated weights, force transducers shall permit the determination of thrust
with an uncertainty of ±5 %.
6.4 Input power
Determination of the power input to the electric motor or to the impeller shall be carried out in accordance
with ISO 5801:2017, Clause 10. P and P are determined by correcting the measured power for a density of
e r
1,2 kg/m .
6.5 Sound level
The sound-level measuring system, including microphones, windshields, cables, amplifiers, and frequency
analyser, shall be in accordance with the requirements given in the ISO 13347 series.
6.6 Vibration velocity
Instruments to measure root mean square (r.m.s.) vibration velocity shall be used to record fan vibration
velocities. These shall be in accordance with ISO 14695.

ISO/DIS 13350:2025(en)
6.7 Volume flowrate
6.7.1 Instruments for the measurement of pressure
Manometers for the measurement of differential pressure and barometers for the measurement of
atmospheric pressure in the test enclosure shall conform with the requirements of ISO 5801:2017, Clause 6.
6.7.2 Instruments for the measurement of temperature
Thermometers shall conform with the requirements of ISO 5801:2017, Clause 8.
7 Determination of thrust
7.1 General
There are two basic configurations acceptable for the determination of fan thrust, T , by direct measurement:
m
— suspended configuration;
— supported configuration.
T is determined by correcting the measured thrust value for a density of 1,2 kg/m , i.e. T = T · 1,2
m m measured
3 3
[kg/m ]/ρ [kg/m ].
a
In addition to the need to measure force accurately, the first method requires that the low friction suspension
elements be kept precisely vertical and parallel with a vertical plane(s) passing through the fan axis, while
the second method requires accurate construction, low friction, and levelling of the support assembly. In
either case, thrust shall be determined by the use of calibrated weights, spring balance, or force transducer.
7.2 Suspended configuration
Figures 3, 4 and 5 show typical arrangements of suspended configurations. The fan is suspended from a
framework or gantry with the suspension elements at least one fan-diameter long. The frame should allow
free airflow, particularly at the fan inlet. Below or surrounding the fan is a rigid framework which serves a
threefold function to:
a) provide the reference point for the fan test assembly under static conditions;
b) provide support for a pulley system to take calibrated weights or a spring balance;
c) provide a reaction point for a force transducer.

ISO/DIS 13350:2025(en)
Key
1 adjustable position of transducer/measuring system
2 air flow
The fan should be accurately levelled prior to testing.
Figure 3 — Thrust measuring layout example (suspended method 1)

ISO/DIS 13350:2025(en)
Key
1 suspension cables 4 adjustable restraint
2 air flow 5 reference point
3 spring balance
The fan should be accurately levelled prior to testing.
Figure 4 — Thrust measuring layout example (suspended method 2)

ISO/DIS 13350:2025(en)
Figure 5 — Thrust measuring layout example (suspended method 3 – centrifugal example)
Under operating conditions, the measuring system loads are adjusted to return the fan to the static positions,
to within ±2 mm, and thus ensure that the suspension elements are precisely vertical. The thrust can then
be measured directly.
Note 1 to entry With the thrust/weight ratios typical of a jet fan, it is doubtful whether the desired accuracy of thrust
measurement can be attained by other means, such as measuring the angle of the suspension elements from the
vertical or the change in height between the fan switched off and operational, and then calculating the thrust.
7.3 Supported configuration
Arrangements of the supported configuration are shown in Figures 6, 7 and 8. The fan is supported, through
low-friction bearings or leaf springs, on a rigid framework. The fan, to an extent limited by stops, is free
to move in either direction. Before commencing any tests, the assembly shall be carefully levelled in each
direction, such that the same effort is required to move the assembly along the axis of the fan in either
direction.
Under operating conditions, the measuring system loads are adjusted to ensure the movement is not being
restrained by the stops. Thrust can then be measured directly. In the case of the use of a force transducer,
the fan can be allowed to abut the sensor directly.

ISO/DIS 13350:2025(en)
Key
1 direction of fan movement 4 fan movement possible
2 air flow 5 thrust gauge (measurement in kg direct off gauge + mass
of gauge in suspension = thrust)
3 bearings
The fan should be accurately levelled prior to testing.
Figure 6 — Thrust measuring layout example (supported method 1)

ISO/DIS 13350:2025(en)
Key
1 direction of fan movement
2 air flow
3 transducer/measuring system
4 bearings
5 fan movement possible
The fan should be accurately levelled prior to testing.
Figure 7 — Thrust measuring layout example(s) (supported method 2)

ISO/DIS 13350:2025(en)
Key
1 direction of fan movement
2 air flow
3 leaf spring
4 load cell
The fan should be accurately levelled prior to testing.
Figure 8 — Thrust measuring layout example (supported method 3)
7.4 Test procedures
To ensure that thrust is measured to the required accuracy, steps shall be taken to minimize errors due
to setting-up/rigging of the test arrangement. Though calibrated weights or spring balances are specified,
if a spring balance is employed to register thrust and it is supported through a pulley, its mass should be
accurately known and added to the measured thrust.
If a force transducer is being used to measure thrust, it is recommended that it is calibrated, for example,
by using a pulley and weight system at no more than 3-monthly intervals. Where the deviation is more than
1 % of the reading, then recalibration shall be reduced to monthly intervals.
Where the supported method is being used, precautions shall be taken to ensure that the force required to
move the fan in either direction is the same and that the assembly is therefore level.
Thrust readings shall be recorded when both the thrust and power input readings have stabilized, or at least
10 min after start-up.
7.5 Test enclosure
Figure 9 shows the clearances required in the test enclosure.

ISO/DIS 13350:2025(en)
Key
1 plane through impeller
2 air flow
3 floor, ceiling, or wall
Figure 9 — a Thrust measuring enclosure – Axial type jet fan

ISO/DIS 13350:2025(en)
Key
1 centrifugal type jet fan
2 air flow
3 floor, ceiling, or wall
Figure 9 — b Thrust measuring enclosure – Centrifugal type jet fan
8 Determination of sound level
8.1 General
The quantity to be determined is the sound power level emitted by the fan – unless otherwise specified, the
total sound power level. This quantity permits an acoustician to calculate the noise level (sound pressure
level) for differing installations, such as the noise level at various locations in a road tunnel or outside tunnel
portals.
Depending on the choice of test method it is possible to measure the total sound power level of the entire
fan, L (tot), or the individual sound power levels of the inlet, L (in) and outlet, L (out). The basis of the
W W W
measured value shall be clearly stated in the test report.
The LW(tot) is the logarithmic sum of all components with total contributions of sound emitted from fan
inlet LW(in), outlet LW(out) and casing LW(cas).
Note The determined LW(tot) will never be lower than the highest of the values determined for the inlet noise
LW(in), the outlet noise LW(out) or the casing break-out noise, where some measuring methods make it hard or even
impossible to separate clearly between the three components, while the sum can be measured more accurately in one go.
The sound power level may be determined by any of the methods described in ISO standards, be it fan-
specific noise measurement standards or more fundamental acoustic standards.

ISO/DIS 13350:2025(en)
8.2 Fan-specific sound measuring standards
The standards mentioned below (ISO 13347-1 to 4), ISO 3740-family and ISO 9614 series are based on
determining the sound power level based on known methods, measuring at defined points all the way
around the fan, with a known accuracy, which can then be used by acousticians for sound calculations. The
practical ad hoc engineering method described in informative Annex A, allows a relative comparison of the
sound emitted by different fans. But its method, measuring mainly at the inlet side which often has less
noise than the outlet side, and definition of distance to reflective surfaces at the inlet only, does not stand up
to scientific scrutiny and modern acoustic measuring metrics. Please note that it has always been incorrect
to measure only the lower noise level of the two openings.
ISO 13347-1 Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
1: General overview
ISO 13347-2 Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
2: Reverberant room method
ISO 13347-3 Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
3: Enveloping surface methods
ISO 13347-4 Fans — Determination of fan sound power levels under standardized laboratory conditions — Part
4: Sound intensity method
8.3 Acoustic standards of the ISO 374X family of documents and the ISO 9614 series sound
intensity methods
Alternatively, any of the Grade 1 or Grade 2 standards of the ISO 374X family of documents for determination
of sound power levels using sound pressure or the ISO 9614 series using soun
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