1.1 Scope
Combination steam ovens are used in the preparation of food within the professional foodservice industry, and are also referred to as combi-ovens, combi-steamers or convection steamers. Combination steam ovens combine traditional convection-based cooking with steam, to offer a range of cooking options within a self-contained appliance. Convection mode is used for baking, grilling roasting and oven-frying, whilst steam mode is used for steaming and poaching food. Combination mode allows for the optimum cooking environment to be created by either adding or removing humidity to the cabinet whilst retaining the food’s moisture and flavour in delivering the browning associated with convection cooking.
1.2 Definitions
Combination steam ovens are fuelled by either electricity or gas. Heat is transferred from the heat generators to the food using separate or combined heat transfer mechanisms. These mechanisms are hot air convection (using either an electrically fuelled heating element or a gas-fired burner to generate heat, and an electrically driven fan(s) to circulate the hot air), saturated steam, or a combination of both (producing super-heated steam). Steam is generated in one of two ways. Injection systems generate steam within the cooking chamber by spritzing water onto a rotating fan(s). Boiler/tank systems generate steam outside the cooking chamber and feed the steam into the cavity as required. Temperatures vary from 30-130°C in steam mode, to 30-300°C in convection and combination modes.
Combination steam ovens contain racks, designed to host containers that correspond with dimensions from the Gastronorm (GN) – fraction-sizing – specification. A 1/1 GN sized container is 530mm (W) by 325mm (L) and a 2/3 GN sized container is 354 x 325mm. Two 1/2 GN containers (265 x 325mm) fit in the footprint of a 1/1 GN, etc. The racks will vary in dimensions, and so are only suitable for certain sizes of containers (e.g., 1/1 GN or 2/3 GN). The number of racks will vary depending on the size of the appliance.
Combination steam ovens are typically categorised into full (1/1 GN), double (2/1 GN), and two-thirds (2/3 GN) size models. They are classified by size and container capacity. The full, double, and two-thirds-size ovens are determined by the number of containers the oven can accommodate per rack position. The container capacity is based on the total number of containers each respective size of oven can accommodate. A double-size combination steam oven can accommodate two 1/1 GN containers per rack position, whereas a full-size combination steam oven can accommodate one 1/1 GN container per rack position. The two-thirds-size combination steam ovens can accommodate one 2/3 GN container per rack position.
There exist tabletop and floor standing combination steam ovens. A tabletop unit is defined as a unit either placed on a table, a stand, any countertop location or stacked on another unit. Floor standing or freestanding combination steam ovens are available with short legs or casters. Floor standing units are displayed solely on the floor as a single independent unit.
Combination steam ovens are available in a range of different designs and efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of higher efficiency products.
The ETL Scheme covers three product-categories according to size:
- Combination steam ovens two-thirds-size 2/3 GN models.
- Combination steam ovens full-size 1/1 GN models.
- Combination steam ovens double-size 2/1 GN models.
The ETL Scheme covers two product-categories according to type:
- Combination steam ovens – Tabletop units.
- Combination steam ovens – Floor standing units.
Products listed on the ETL will be presented according to the above size and type categorisation. To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.
1.3 Requirements
1.3.1 Eligibility requirements
To be eligible, products shall:
- Be either electric (single/three phase) or gas fuelled.
- Have an appropriate Conformity Assessment mark.
1.3.2 Performance requirements
Eligible products shall meet the performance criteria set out in Table 1.1.
Table 1.1 Performance requirements for combination steam ovens
| Fuel | Maximum Energy Consumption in Convection Mode for a Loaded Oven (kWh/stone)[1] |
| Electricity | 0.26 kWh |
| Gas | 0.27 kWh |
Suppliers shall report the following performance parameters for each model, which will be published on the ETL Product Search:
- Heating-up time (minute: seconds) in convection mode.
- Energy (kWh) and water consumption (litres) in convection mode for an empty appliance.
- Energy (kWh) and water consumption (litres) in convection mode for a loaded appliance.
- Convection mode cooking efficiency (η).
1.4 Measurement and Calculations
1.4.1 Measurement Standards
Both electric and gas products shall be tested according to BS EN 50733:2025. Since the BS EN 50733:2025 is focused entirely on electric products, for gas products the volume of gas consumed during each test should be measured and the RUI formulae in section 7.10.103 of BS EN 203-2-2-1: 2021 + A1: 2023 can be used to calculate the energy consumed in kWh corrected to standard conditions during the tests. The accuracy requirements for measuring equipment set out in Section 7.1.8 of BS EN 203-1: 2021 + A1: 2023 should be respected.
- BS EN 50733:2025: Electric forced convection ovens, steam cookers and combination ovens for professional use – Test methods for measuring performance.
- BS EN 203-2-2:2021+A1:2023: Gas heated catering equipment - Specific requirements - Ovens
Products tested under the ETL testing process and the DIN 18873-1:2012 are accepted until further notice.
1.4.2 Testing processes
The products shall be tested in different modes and conditions:
- Models shall undergo energy performance testing in the default mode set as the models are shipped, while adhering to the standard test methodology.
- Models shall be tested empty and under load while operating in convection mode.
- For the testing under load in convection mode, a specified amount of weight of saturated Hipor-Stones per grid are placed in the cavity of the appliance.
1.4.3 Metric measurements
- The heating-up time (minute: second) for the product to reach a specific temperature level while operating in convection mode shall be recorded.
- The energy consumption (kWh) of the product shall be recorded over the series of testing procedures.
- The water consumption (litres) of the product shall be recorded over the series of testing procedures.
1.4.4 Rounding
For the avoidance of doubt, test data should be presented to 3 decimal places. For example, an electric model’s energy consumption per stone of 0.261 kWh would be considered ineligible under these criteria.
1.5 Verification for ETL Listing
Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:
- In-house testing – Self-tested and verified or cross-checked by an independent body.
- Witnessed testing.
- Independent testing.
- Representative testing (see clause 1.5.1 below).
Further information regarding the first three routes can be found in the ETL Testing Framework.
1.5.1 Representative testing
Where applications are being made for two or more models that are variants of the same basic design, test data may be submitted for a single ‘representative model’ provided that all variants:
- Use the same fuel.
- Belong to the same size product category (i.e., full, double, or two-thirds size models).
- Can accommodate the same total number of containers (e.g.,10) of equivalent dimensions.
- Have the same rack dimensions (e.g., 1/1 GN).
- Have the same or less energy consumption values (kWh) while operating in convection mode.
It should be noted that:
- Models that are variants of the same basic design are defined as all professional oven equipment which belong to the same product family and are manufactured by a single manufacturer, with the same primary power or energy source. All physical and functional characteristics shall be identical. Aesthetic changes are acceptable as long as the energy consumption and performance are not impeded.
- If a manufacturer voluntarily removes the representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL.
- If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative model will be removed from the ETL.
1.6 Conformity testing
Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.
1.7 Review
1.7.1 Indicative review date
This specification is scheduled to be reviewed during the 2028/29 review cycle.
1.7.2 Illustrative future direction of the requirements
The next technical review will look to strengthen the performance thresholds for electric and gas-fuelled combination ovens and consider amending the current performance thresholds from an absolute to an efficiency parameter, in light of the performance data collected during the intervening period. Additionally, the development of differentiated performance thresholds will be explored to account for variations in performance across different model sizes.
The next technical review will also consider the setting of performance thresholds for steam and combination modes.