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Department for Business, Energy and Industrial Strategy

Warm Air Heating Equipment

1.1    Scope

Warm air heating equipment covers products that are specifically designed to provide space heating by using the heat generated by a burner to raise the air temperature in the space(s) being heated, and optimising controllers that ensure warm air heating systems operate in an efficient manner.

1.2    Definitions

Warm air heaters are widely used to provide space heating for warehouses, retail sheds, sports centres, factories, and other buildings containing similarly large spaces. Warm air heaters contain a gas or oil-fired burner that is used to heat the air in the space directly, or indirectly by means of a heat exchanger. A fan is used to distribute the warm air throughout the space(s) being heated. 

Warm air heaters are available in a range of different types and efficiencies. The Energy Technology List (ETL) Scheme encourages the purchase of higher efficiency warm air heaters. It also encourages the purchase of optimising controllers that ensure that warm air heating products and systems operate in an energy efficient manner that reflects weather conditions, occupation schedules and user requirements. 

The ETL Scheme covers three categories of product:  

  1. Indirect fired condensing packaged warm air heater units including on/off, high/low and fully-modulating type products. 
  2. Indirect fired condensing packaged air heater modules including on/off, high/low and fully-modulating type products. 
  3. Optimising controllers for warm air heating systems including both standalone unit and add-on module type products. 

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, all products shall comply with the relevant requirements set out below: 

  1. All products incorporating warm air heaters shall: 
    -    Be gas or oil-fired (where gas includes biogas and oil includes liquid biofuels). 
    -    Be designed to be permanently installed in one of the following ways: 
       a)    As a suspended, wall mounted or floor-standing unit. 
       b)    As a heating module within an air handling unit. 
    -    Incorporate a fan to distribute warm air within the heated space, unless they are warm air heating modules that are specifically designed to be installed in an air handling unit. 
    -    Have an appropriate Conformity Assessment mark.
  2. All products that incorporate optimising controllers shall: 
    -    Incorporate a microprocessor based controller that is pre-programmed to: 
       a)    Automatically control the air temperature in one or more zones within a building in an energy efficient manner that reflects predefined zone occupation schedules. 
       b)    Automatically switch warm air heating equipment on and off in accordance with the predefined occupation schedule for each of the zones being controlled. 
    -    Incorporate the following automatic control mechanisms: 
       a)    An optimum start mechanism that monitors external and/or internal temperatures, and calculates when the warm air heating equipment need to be switched on in order to just reach pre-set temperatures by the start of the next occupancy period. 
       b)    A “self-learning” algorithm that automatically monitors the accuracy of the optimum start mechanism and periodically updates the heating curve that the mechanism uses, to reflect changes in building characteristics.
       c)    A frost protection mechanism that monitors internal air temperature, and switches on the warm air heaters to prevent equipment and/or pipework from freezing up. 
       d)    A building fabric protection mechanism that monitors external or internal temperatures and switches heating on to prevent condensation from occurring. 
       e)    An anti-tampering mechanism that prevents the product’s control strategy from being modified, and the specified automatic control mechanisms from being disabled, except during commissioning, maintenance or testing. 
    -    Provide facilities that enable building managers to: 
       a)    Define the normal occupation times for the building and for each zone controlled (in intervals of five minutes or less), for each day of the week, including at least two periods of occupation per day (i.e. at least 14 different occupation periods per week). b) Define the temperature set-points for each zone to ±1°C. 
       b)    Define future dates (e.g. holidays) when the warm air heating equipment should be completely switched off, or operated at frost, fabric or equipment protection levels. 
    -    Provide facilities that enable building users to “temporarily override” the pre-set times when the warm air heating is scheduled to be switched off within an individual zone. 
    -    Conform to the requirements of the The Electromagnetic Compatibility Regulations 2016 or have an appropriate Conformity Assessment mark.


  1. A mechanism is defined as “any sequence of pre-defined actions that performs a given function, where an action can be defined in hardware and/or software terms”. 
  2. Products that incorporate control strategies that are specifically designed to control other types of equipment (other than warm air or radiant heaters) are not eligible.

1.3.2    Performance requirements

All products shall have a seasonal space heating energy efficiency that is greater than or equal to 80.0%. 

1.4    Measurement and calculations

1.4.1    Performance metric and Measurement standard

The product’s seasonal space heating energy efficiency shall be determined in accordance with the method set out in:  

  • Commission Regulation (EU) No 2016/2281 implementing Directive 2009/125/EC of the European Parliament and of the Council establishing a framework for the setting of Ecodesign requirements for energy-related products, with regard to Ecodesign requirements for air heating products, cooling products, high temperature process chillers and fan coil units. 

1.4.2    Rounding  

For the avoidance of doubt seasonal space heating energy efficiency test data shall be presented to 1 decimal place. As an example, a warm air heater unit with a seasonal space heating energy efficiency of 79.9% would be deemed to not meet the performance requirements.

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-certified
  • 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)

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 a range of two or more products that are variants of the same basic design, test data may be submitted for a representative selection of models, provided that all variants:

  • Use the same fuel (e.g. oil or gas) as the representative model.
  • Fit within the same product category (e.g. are all indirect fired condensing packaged warm air heater units) as the representative model.
  • Have the same control mechanism (e.g. are all fully-modulating warm air heater units) as the representative model.

The representative models shall be selected by dividing the range of products into groups of models with similar characteristics, as above, and testing a model in each group. The performance of each model in the group shall be predicted by extrapolation or interpolation or by using a validated mathematical model. As a minimum, a full test report shall be provided for at least one model tested in each range of products. Details of the calculation method used in determining the performance of models that have not been tested shall also be provided.

It should be noted that:

  • 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 will be reviewed during the 2022/23 ETL review period.

1.7.2    Illustrative future direction of the requirements  

The eco-design Tier 2 Minimum Energy Performance Standards for this category of products is due to come into force on 1 January 2021. At this time, there may be some scope to increase performance thresholds; however, the technology is close to its energy efficiency limits. Future requirements may look to encourage the use of ‘green’ gases with lower carbon emissions than oil and natural gas. 

A new test standard has also been introduced to enable performance measurement for the Ecodesign regulation for warm air heaters. This is currently under provisional status and is therefore not included in this specification. Future requirements will reference the finalised version of the new test standard when it comes into force.