ISO 21364-21:2025

International
Standard
ISO 21364-21
First edition
Domestic gas cooking appliances —
2025-06
Safety —
Part 21:
Particular requirements for gas
hobs, gas grills and gas griddles
Appareils de cuisson domestiques utilisant les combustibles
gazeux — Sécurité —
Partie 21: Exigences particulières pour les tables de cuisson à gaz,
grils à gaz et grils par contact à gaz
Reference number
© ISO 2025
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ii
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
3.1 Definitions relating to components .2
4 Components in gas cooking appliances . 2
4.1 General .2
4.2 Manual gas shut-off valves .2
4.3 Knobs.3
4.3.1 Design of knobs.3
4.3.2 Marking for knobs .3
4.4 Multifunctional controls .3
4.5 Thermoelectric flame supervision controls .3
4.6 Thermostats . .3
4.7 Pressure regulators .3
4.8 Automatic shut-off valves.3
4.9 Injectors and adjusters . .3
4.10 Ignition systems .3
4.11 Thermal cut-outs .3
4.12 Multi-ring burners .3
4.13 Overheating safety devices (OSD) .4
4.13.1 Requirement .4
4.13.2 Test procedure.5
5 General conditions of test . 5
6 Heat input . 5
6.1 General .5
6.2 Obtaining the nominal heat input . .5
6.2.1 General .5
6.2.2 Test of hob burner .5
6.2.3 Test of multi-ring hob burner .6
6.2.4 Test of surface grill and griddle without a thermostat .6
6.2.5 Test of surface grill and griddle with a thermostat .6
6.3 Measurements and calculations .6
6.4 Obtaining the reduced heat input .6
6.4.1 General .6
6.4.2 Test of hob burner, surface grill and griddle burner .6
6.5 Total heat input .6
7 Heating . 6
7.1 General .6
7.2 Operating conditions .6
7.3 Heating tests .7
7.4 Abnormal operation .7
7.4.1 General .7
7.4.2 Hob burner .7
7.4.3 Gas griddles . .7
8 Combustion . 7
8.1 Measurement of all burners simultaneously .7
8.2 Blocked combustion products outlet .7
8.3 Analysis of the combustion products .8
8.4 Single burner .8
8.4.1 General requirement . .8

iii
8.4.2 Hob burner, surface grill burner and griddle burner .8
8.4.3 Tests of multi-ring burner .9
8.4.4 Additional test of Type II and Type V multi-ring burners .10
8.4.5 Sampling the combustion products .10
8.5 Sooting test . 13
8.5.1 Requirement . 13
8.5.2 Test . . . 13
9 Ignition, cross-lighting and flame stability . 14
9.1 General .14
9.2 Movement of oven/grill door or cabinet door .14
9.3 Test for appliances having an automatic burner control system.14
9.4 Hob burner, surface grill burner and griddle burner .14
9.4.1 General .14
9.4.2 Cold conditions . .14
9.4.3 Hot conditions . 15
9.5 Multi-ring hob burner.16
9.5.1 Requirement .16
9.5.2 Additional test for Type I multi-ring burners .16
9.5.3 Additional test for Type II and Type V multi-ring burners .16
9.5.4 Resistance to draught .17
10 Accumulation of unburnt gas and leak tightness .18
11 Construction .18
11.1 General .18
11.2 Materials .19
11.2.1 General .19
11.2.2 Burner material test .19
11.2.3 Sealings .19
11.2.4 Resistance for non-metallic feet of pan supports .19
11.3 Gas inlet connections .19
11.4 Conversion to different gases .19
11.5 Pull forces of knobs for manual gas shut-off valves.19
11.6 Appliances that enable the user to program the start or the end of the cooking cycle .19
11.7 Compartment for one gas cylinder .19
11.8 Touch controls .19
11.8.1 General .19
11.8.2 Requirement . 20
11.8.3 Test . . . 20
11.9 Resistance to spillage . 20
11.9.1 Requirement . 20
11.9.2 Test . . . 20
11.10 Specific hob parts and hob accessories . 20
11.10.1 Pan supports . 20
11.10.2 Removable devices for small pans .21
11.10.3 Special supports for convex-based pans .21
11.10.4 Covered burners .21
11.11 Shut down lids .21
11.11.1 Requirement .21
11.11.2 Test . . . 22
11.11.3 Glass shut down lids . 22
11.11.4 Shut-off device . 22
12 Mechanical strength .23
12.1 Parts made of glass and glass-ceramic . 23
12.1.1 General . 23
12.1.2 Spring hammer test . 23
12.1.3 Punch test . 23
12.1.4 Thermal stress resistance for glass and glass-ceramic hob surfaces . 23
12.2 Pan support . 23

iv
12.2.1 Requirement . 23
12.2.2 Test . . . 23
12.3 Pan support in contact with the glass or glass ceramic of the hob . 23
13 Electrical safety .24
14 Marking and instructions .24
Annex A (normative) National deviations in various countries.25
Annex B (informative) Additional tests for hobs, surface grills and griddles supplied with
natural gas and hydrogen admixtures .28
Annex C (informative) Additional combustion test for NO measurement of gas hobs burners .33
Bibliography .35

v
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,
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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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
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this may not represent the latest information, which may be obtained from the patent database available at
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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 291, Domestic gas cooking appliances.
This first edition of ISO 21364-21:2025 cancels and replaces ISO/TS 21364-21:2021.
A list of all parts in the ISO 21364 series can be found on the ISO website.
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.

vi
Introduction
Gas burning appliances using fuel gases must withstand the type of gas which is specified. Other International
Standards cover the testing and properties of fuel gases.
Due to the differing properties of fuel gas depending on its source and region of origin, certain differences in
regulations exist in different regions at present; some of these differences are presented in Annex A.
This document is designed to be used in combination with ISO 21364-1. Together, they establish the
requirements to the product covered by this document. Where needed, this document adapts certain
requirements from ISO 21364-1 with amendments such as:
— “with the following modification”;
— “with the following addition”;
— “is replaced by the following”;
— “is not applicable”.
In order to identify specific requirements that are particular to this document, and not already covered by
ISO 21364-1, this document contains clauses or subclauses that differ to the structure of ISO 21364-1.
To ensure the global relevance of this document, the differing requirements resulting from practical
experience and installation practices in various regions of the world are taken into account. The variations
in basic infrastructure associated with appliances are also taken into account, some of which are addressed
ISO 21364-1, Annex E and Annex A of this document. This document intends to provide a basic framework of
requirements that recognize these differences.

vii
International Standard ISO 21364-21:2025(en)
Domestic gas cooking appliances — Safety —
Part 21:
Particular requirements for gas hobs, gas grills and gas
griddles
1 Scope
This document specifies requirements for safety, construction and materials of household gas surface
cooking appliances.
NOTE 1 For general requirements regarding safety, construction and materials of household gas surface cooking
appliances, see ISO 21364-1.
This document is applicable to the following:
— the following surface cooking appliances, being built-in, part of a cooking appliance or table top:
— hobs;
— surface grills;
— griddles;
— hobs accessories.
It is not applicable to surface cooking appliances intended for either outdoor use or commercial use, or both,
as well as electrical heated elements as part of the appliance.
NOTE 2 For requirements regarding electrical safety, refer to the IEC 60335 series.
NOTE 3 Attention is drawn to the fact that:
— for appliances intended to be used in vehicles or on board of ships or aircrafts, additional requirements can apply;
— in many countries, additional requirements are specified by the national health authorities, the national water
supply authorities and similar authorities.
This document does not cover requirements relating to gas cylinders, their pressure regulators and their
connections.
This document does not cover requirements for gas installation.
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 21364-1, Domestic gas cooking appliances — Safety — Part 1: General requirements
ISO 23551-8:2016+AMD1:2019, Safety and control devices for gas burners and gas-burning appliances —
Particular requirements — Part 8: Multifunctional controls

IEC 60730-2-9, Automatic electrical controls for household and similar use — Part 2-9: Particular requirements
for temperature sensing controls
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21364-1 and the following apply.
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 Definitions relating to components
3.1.1
open burner
hob burner with the flame in direct contact with the pan
3.1.2
multi-ring burner
hob burner assembly having two or more rings of burner ports
Note 1 to entry: The term ring includes any distribution of burner ports around the central axis of the burner.
Note 2 to entry: A detailed description of the different types of multi-ring burners and their operating modes is given
in Table 1.
3.1.3
multi-ring burner with sectional control
multi-ring burner (3.1.2) that is designed so that one or more of its rings of burner ports can be utilised
independently
3.1.4
multi-ring burner with simple control
multi-ring burner (3.1.2) that is designed so that its rings of burner ports cannot be utilised independently
3.1.5
overheating safety device
OSD
temperature sensing device which is intended to keep temperature below one particular value during
abnormal operating conditions of the appliance and which has no provision for setting by the end user
Note 1 to entry: These devices usually use a thermistor or a bimetal sensing part (element).
4 Components in gas cooking appliances
4.1 General
ISO 21364-1:2025, Clause 4.1 shall apply in addition to the requirements specified in Clause 4 of this
document.
4.2 Manual gas shut-off valves
ISO 21364-1:2025, 4.2 shall apply with the following addition.
For multi-ring hob burners, the “off” position of a single sectional control with two closing directions shall
be designed to make it impossible for the knob to be inadvertently moved from one adjustment range to

another. However, if each ring of such multi-sectional hob burner is supervised by a flame supervision device
(FSD), the single sectional control shall stop in its “off” position.
4.3 Knobs
4.3.1 Design of knobs
ISO 21364-1:2025, 4.3.1 shall apply with the following addition.
If the control knob of a multi-ring burner operates by turning, the closing direction shall only be clockwise.
This does not apply to multi-ring hob burners with a single sectional control and two closing directions.
4.3.2 Marking for knobs
ISO 21364-1:2025, 4.3.2 shall apply.
4.4 Multifunctional controls
ISO 21364-1:2025, 4.4 shall apply.
4.5 Thermoelectric flame supervision controls
ISO 21364-1:2025, 4.5 shall apply.
4.6 Thermostats
ISO 21364-1:2025, 4.6 shall apply.
4.7 Pressure regulators
ISO 21364-1:2025, 4.7 shall apply.
4.8 Automatic shut-off valves
ISO 21364-1:2025, 4.8 shall apply.
4.9 Injectors and adjusters
ISO 21364-1:2025, 4.9 shall apply.
4.10 Ignition systems
ISO 21364-1:2025, 4.10 shall apply.
4.11 Thermal cut-outs
ISO 21364-1:2025, 4.11 shall apply.
4.12 Multi-ring burners
Table 1 shows examples of multi-ring burners and their operating modes.

Table 1 — Examples of types of multi-ring burners and their operating modes
Key 5 gas supply
1 inner burner-ring 6 connection to FSD
2 outer burner-ring 7 alternative connection to FSD
3 flame supervision sensor
4 manual gas shut-off valve
FSD at inner or outer FSD at inner or outer FSD at inner and FSD at inner and FSD at inner or
burner ring burner ring outer burner ring outer burner ring outer burner ring
Type I Type II Type III Type IV Type V
Simple control Sectional control Sectional control Two single controls Sectional control
with two turning with two turning
directions directions
Multi-ring burner that Multi-ring burner that Multi-ring burner Multi-ring burner Multi-ring burner
is designed so that its is designed so that one that is designed so that is designed so that is designed so
rings of burner ports or more of its rings of that one or more of that it has two or that its control has
cannot be utilized inde- burner ports can be its rings of burner more manual gas two turning direc-
pendently, controlled utilized independently, ports can be utilized shut-off valves each tions. One direction
by a manual gas shut-off controlled by a manual independently, con- with one outlet for is for utilizing one
valve with one outlet for gas shut-off valve with trolled by a manual separate supply of burner ring. The
common supply of all two or more outlets for gas shut-off valve the burner rings other direction is to
burner rings with one separate supply of the with two or more and same turning utilize both burner
turning direction. burner rings with one outlets for separate direction. rings.
turning direction. supply of the burner
rings with two turn-
ing directions. The
two rings cannot be
operated together.
4.13 Overheating safety devices (OSD)
4.13.1 Requirement
An OSD, if any, shall conform with the requirements in ISO 23551-8:2016+A1:2019, Annex BB.
Electrical safety requirements for the OSD shall conform to IEC 60730-2-9.
An OSD for a gas hob shall be as follows:
a) when tested according 4.13.2, the OSD shall prevent the oil temperature exceeding 300 °C;
b) when the thermal sensing part is damaged, the gas passage to the burner shall be closed and shall not be
reopened automatically;
c) for circuit failure or short-circuit, the gas passage to the burner shall be closed and shall not be reopened
automatically;
d) the temperature sensing part of the OSD shall be secured firmly, in a way that it cannot be easily moved
to a wrong position;
e) the OSD shall have a structure in which it cannot be easily altered;
NOTE If a special tool or dedicated terminal is used, this requirement is deemed to be fulfilled.
f) after applying a load conforming to 12.2 to a cooking appliance, the temperature sensing part shall
operate as normal.
4.13.2 Test procedure
The test shall proceed as follows:
a) Select test pan according to ISO 21364-1:2025, Table 3.
b) Fill the pan with unused cooking oil to a depth of 10 mm.
c) A thermocouple is placed in the centre of the oil volume.
d) Use reference gas at normal pressure.
e) Operate the burner at nominal heat input. Measure the highest temperature of oil as the OSD is
functioning.
5 General conditions of test
ISO 21364-1:2025, Clause 5 shall apply.
6 Heat input
6.1 General
ISO 21364-1:2025, Clause 6 shall apply in addition to the requirements specified in Clause 6 in this document.
6.2 Obtaining the nominal heat input
6.2.1 General
ISO 21364-1:2025, 6.2 shall apply, with the following additions.
6.2.2 Test of hob burner
The measurements are taken with the burner operating under the following conditions:
— a pan is placed on an open burner in accordance with ISO 21364-1:2025, 5.7 without a lid and filled with
water to a level of (50 to 65) mm above the bottom of the pan;
— with the appliance at ambient temperature, the burner is ignited and operated at full rate at normal
pressure for 10 min;
— measurement starts at the end of the tenth minute and finishes at the latest at the end of the thirteenth
minute, with a minimum measurement time of one minute or when the highest number of complete
revolutions of the meter have been made before the end of the thirteenth minute. For analogue meters,
the measurement shall be taken over at least one complete revolution.
Then the heat input is calculated under reference conditions according to ISO 21364-1:2025, 6.3.

6.2.3 Test of multi-ring hob burner
All burner rings are measured according to 6.2.2 when operated together. Multi-ring burners with separate
controls for each burner ring (Type IV, see 4.12) are measured separately.
6.2.4 Test of surface grill and griddle without a thermostat
The burner of a surface grill and a griddle without a thermostat is tested under the following conditions:
— surface grills and griddles are tested without a pan;
— with the appliance at ambient temperature, the burner is ignited and operated at full rate at normal
pressure for 10 min;
— measurement starts at the end of the tenth minute and finishes at the latest at the end of the thirteenth
minute, with a minimum measurement time of one minute or when the highest number of complete
revolutions of the meter have been made before the end of the thirteenth minute. For analogue meters,
the measurement shall be taken over at least one complete revolution.
Then the heat input is calculated under reference conditions according to ISO 21364-1:2025, 6.3.
6.2.5 Test of surface grill and griddle with a thermostat
Surface grills and griddles are tested without a pan. Measuring begins from ignition, with the thermostat
or control device at full rate and terminates at the end of the fifth minute or when the highest number of
complete revolutions of the analogue meter have been made before the end of the fifth minute. The test shall
be finished before the thermostat starts cycling.
Then the heat input is calculated under reference conditions according to ISO 21364-1:2025, 6.3.
6.3 Measurements and calculations
ISO 21364-1:2025, 6.3 shall apply.
6.4 Obtaining the reduced heat input
6.4.1 General
ISO 21364-1:2025, 6.4 shall apply with the following addition.
6.4.2 Test of hob burner, surface grill and griddle burner
The reduced heat input shall be measured after the nominal heat input according to ISO 21364-1:2025, 6.4.
6.5 Total heat input
ISO 21364-1:2025, 6.5 shall apply.
7 Heating
7.1 General
ISO 21364-1:2025, Clause 7.1 shall apply.
7.2 Operating conditions
ISO 21364-1:2025, 7.2 shall apply.

7.3 Heating tests
ISO 21364-1:2025, 7.3 shall apply.
7.4 Abnormal operation
7.4.1 General
ISO 21364-1:2025, 7.4 shall apply with the following additions.
7.4.2 Hob burner
7.4.2.1 Requirement
During the test in 7.4.2.2, the temperature rise shall not exceed the values specified in ISO 21364-1:2025, 7.4,
Table 7.
7.4.2.2 Test
Pans with the biggest diameter allowed in the instruction for use and maintenance are placed according
ISO 21364-1:2025, 7.3.2.2. If no maximum pan size is given in the instructions for use, use a pan with a
diameter 60 mm bigger than the one given in ISO 21364-1:2025, 5.7, Table 3. The pans are placed on each
hob burner and electric cooking plate, starting with the special pans. No pan shall overlap the edges of the
hob. A distance of at least 10 mm shall be provided between the side surface of each pan and all other pans.
If this arrangement is not possible, pans with a smaller diameter according to ISO 21364-1:2025, 5.7, Table 3
are used.
During the test, the pans are used with lids. Hot water is added to ensure that water is always present in the pans.
All hob burners are operated for 1 h or up to steady conditions, whichever is shorter, with one of the
reference gases (according to the corresponding table of ISO 21364-1:2025, Annex A) at nominal heat input
with normal pressure, their control being at full rate.
NOTE Steady conditions are deemed to have been achieved when the measured temperatures do not vary by
more than 1 K in 15 min.
7.4.3 Gas griddles
7.4.3.1 Requirement
During the test in 7.4.3.2, the temperature rise shall not exceed the values specified in ISO 21364-1:2025, 7.4,
Table 7.
7.4.3.2 Test
Griddles are operated without a pan for 1 h or up to steady conditions, whatever is shorter, with one of the
reference gases at nominal heat input, their control being at full rate.
8 Combustion
8.1 Measurement of all burners simultaneously
ISO 21364-1:2025, 8.1 shall apply.
8.2 Blocked combustion products outlet
ISO 21364-1:2025, 8.2 shall apply.

8.3 Analysis of the combustion products
ISO 21364-1:2025, 8.3 shall apply.
8.4 Single burner
8.4.1 General requirement
Under the conditions described below, the CO concentration in the dry and air-free combustion products for
each of the burners shall not exceed:
— 0,10 % for Test no. 1;
— 0,15 % for Tests no. 2 and 3;
— 0,20 % for Test no. 4.
Burners or burner sections having a maximum heat input less than 600 W are not subjected to combustion
testing.
The requirements for the tests are given in Table 2.
8.4.2 Hob burner, surface grill burner and griddle burner
8.4.2.1 General
The appliance shall be installed according to ISO 21364-1:2025, 5.6, but without the horizontal wooden
panel or range hood above the appliance. An additional panel at the minimum distance as stated in the
instructions for installation is installed on that side of the appliance where the burner with the highest heat
input is located, or whichever side results in the worst-case test condition. Any gaps allowing air to pass
through between the side panel and the back panel are sealed
...