BS8303 standard update

BS8303 standard update

In the latest HETAS Technical Bulletin we updated our registrants on the imminent changes to BS8303. In this article we highlight some of the key changes to the standard that will impact upon registered installers.

Over recent years, the industry through the UK BSI standards committee RHE/28 have been working hard in reviewing and updating the requirements contained in the solid fuel recognised standard BS 8303: 1994 Installation of domestics heating and cooking appliances burning solid mineral fuels. With the new standard due for publication and release in the coming days, it is important for registered installers and other industry personnel to be aware of the relevant changes, which include more up-to-date installation practices that better reflect the products and materials available on today’s market.

HETAS will continue to publish ongoing information to its registrants on the new alternative approaches contained within the BS 8303 standard through its technical bulletin publications, as well as an update to the current HETAS H003 and H003 refresher training courses to include the relevant requirements.

Application of the Standard

HETAS continue to receive queries relating to the appropriate application of any provisions contained within recognised BSI standards, and how they can be applied with continued re-assurance in meeting the UK Building Regulation requirements. For solid fuel installations, page 40 of Approved Document J gives clear guidance on this issue by means of stating the following;

Alternative Approach

The requirements may also be met by adopting the relevant recommendation in the publications listed below to achieve a level of performance equivalent to that obtained by following the guidance in this Approved Document:

  1. BS EN 15287-1 Design, Installation & Commissioning of chimneys for non-room-sealed heating appliances
  2. BS 8303 Installation of domestic heating and cooking appliances burning solid mineral fuels

The important part of this statement is the word “equivalence”, which ensures that by way of adopting the approaches given in these two recognised standards that the installation is no less safe than what would occur by following the technical guidelines given within the Approved Document.

So what will change?

With the original standards last publication coming in 1994, the new standard will look more closely at covering the basic requirements surrounding more highly efficient closed appliances, and base less emphasis on new installation of inefficient opened fire appliances (covered in more detail in BS 1251:2015). This will include provisions for the hearth, recess construction, closure/register plate, air supply and maintenance.

There are two principle additions to the upcoming standard amongst the other covered that were not previously contained within the 1994 version, mainly constituting requirements for

  • The appropriate heat shielding of a freestanding appliance (not situated in a builder’s recess) up to 7kW nominal output in scenarios of lightweight timber construction properties
  • Information on the design, installation and assessment procedures relating to the installation of dedicated external air supply appliances.

The annex will also include updated commissioning guidance relating to the methods for commissioning flues and installations of varying types, using the industry recognised smoke and spillage test procedures.

Shielding of Combustibles

The standard will contain caveats for the appropriate protection of combustible materials when using a shield in a freestanding configuration, and state the required clearance and air gaps distances. In particular;

  • Use of a 1.5mm galvanized steel metal shield, affixed with non-combustible fixings to maintain an air gap of 25mm between the shield and the wall
  • Shield protrudes at least 300mm above the top surface of the appliance and extend to the edge of the hearth horizontally
  • The shield shall be open top and bottom to allow the flow of cool air between the shield and the wall
  • Distance from the appliance rear to the outer surface of the shield of at least 95mm and at least 90mm from the side of the appliance to the outer surface of the shield (if near to an adjacent wall)

Dedicated External Air Supply

The annex to the new BS 8303 will contain information to the appropriate design, assessment and commissioning of appliances with a dedicated external air supply, in line with HETAS technical guidance document HETAS_TN_0020. These include;

  • Ensuring installation of a dedicated external air supply kit is completed in line with manufacturer’s instructions, including consideration for the duct diameter, total length, air inlet terminal position and duct material specification
  • Appropriate risk assessment and commissioning procedures are undertaken to understand the properties current ventilation and air tightness, appliance roomsealed properties and again ensuring manufacturer instructions are available and met.
  • Appropriate smoke tests are completed, including with any extract running, and spillage test when the door is opened for refuel.

Further details and assessment/commissioning forms are available within the current version of HETAS_TN_0020, which is available on the technical area of the HETAS website at

If you have a technical question you can contact the team on 01684 278194 or email


Going Direct

Going Direct

HETAS has developed a simplified technical guidance document which covers the relevant direct air assessment and commissioning procedures that installers can refer to in conjunction with any manufacturers requirements.

For self-certification of direct external air supply appliances, it is imperative that the installer understands the relevant safety provisions. Where a copy of the manufacturer installation instructions can be obtained this must be read and understood before work begins. If there is no information saying that the appliance can be used with a direct air supply and there is no air supply kit specified, HETAS recommends that the appliance is not fitted with a direct air kit. Alternative ventilation must be provided if required.


The following considerations should be taken into account:

  • Whether the manufacturers’ instructions confirm that the appliance can be safely installed in this way and the manufacturer has provided clear guidance on installing the appliance and air kit together.
  • Whether the dedicated air kit used meets the manufacturer’s requirements and the appliance is fitted in accordance with manufacturer’s instructions.
  • The installer must assess the installation and commission the appliance in accordance to manufacturer’s instructions and ensure HETAS commissioning and risk assessment guidelines are adhered to and evidenced correctly.
  • If at commissioning stage the appliance cannot be confirmed as operating safely, it should be disconnected from the chimney and placed somewhere that it can’t be used.
  • In some cases where spillage testing indicates poor flue performance, it may be that an ADJ vent is the only solution to supplying additional air for safe and correct operation. In this case the consumer should be advised of this compliance requirement and changes made to make the installation safe.

As well as manufacturer installation guidelines, it is essential that there are relevant assessments of the installation environment. These will involve assessment of the constructional attributes of the property, including any previous heat loss improvement measurements (cavity wall insulation, draft proofing etc.), as well as the current method of providing habitable and combustion ventilation, appliance type and the installation design providing efficient operation of the appliance.

Property Type

Properties built after 2008 are likely to incorporate more stringent energy efficiency measures, and as a result have more airtight construction characteristics; these will need to be factored in during any assessment of the installation. Careful consideration should therefore be taken to confirm the type of appliance selected is suitable for installation and operation under roomsealed conditions, and verified by the manufacturer as taking 100% of its air for combustion directly from outside.

Appliances verified by the manufacturer as non-roomsealed may require additional permanent ventilation in the room to ensure continued draw on the flue, especially under conditions of refuel. In these cases it is important to reference the applicable installation instruction guidance or seek further clarification from the appliance manufacturer on appropriate size and positioning of this additional ventilation requirement.

As well as constructional characteristics of the property, ventilation interference should be carefully considered, particularly in cases where mechanical and heat recovery extract systems are incorporated into the dwelling. When operated, these may cause depressurisation in the room or adjoining rooms in which the appliance is installed. Assessing these areas and carrying out appropriate spillage tests during initial light up and refuel phases allows for confirmation and sign off of the safe operation of the appliance during both extraction and non-extraction scenarios.

Installation Design

The final area of assessment is in relation to installation design. It is imperative at this stage for the installer to follow manufacturer specifications for the design of the air supply duct to the outside atmosphere, paying particular attention to the following areas:

  • Minimum diameter or cross sectional area of the external air duct
  • Maximum total length of the duct
  • Maximum number of bends permitted
  • Specification of the air inlet terminal
  • Measures to be taken to prevent the air supply becoming blocked by debris, flooding, insect habitats etc.

The area designated by the hearth dimensions is a non-combustible zone, and any material used for the duct within this area must be of a non-combustible material and not affected by heat. It is advised to only install a dedicated external air kit supplied or specified by the manufacturer of the appliance who will have taken this into account, ensuring the product can be installed in a way that is deemed compliant.

Additional Guidance

To aid installers further, HETAS have issued a Direct External Air Supply (DEAS) technical note for guidance on the installation, risk assessment and commissioning of solid fuel batch fed appliances. A copyof the document can be obtained from the HETAS Technical Area.

Get in touch

To discuss this article or any other technical related questions contact the HETAS Technical Helpline on 01684 278194.

HETAS Technical Bulletin 8

HETAS Technical Bulletin 8HETAS Technical Bulletin 8 Cover

Last week we published HETAS Technical Bulletin 8 with updates on hot topics, including an update on direct air guidance, system chimneys and distance to combustibles, commissioning records and the latest FAQ’s from the helpline team. All the Technical Bulletins are available in the HETAS Technical Area.

The eighth installment of the HETAS Technical Bulletin. In this edition of the bulletin we include updates on the following topics:

  • Complying with the Energy Labelling Directive
  • Revision of the HETAS Commissioning Record
  • Further Guidance for Direct External Air Supply
  • Latest from the Technical Helpline
  • Metal System Chimneys and Clearances to Combustibles

As well as giving our stakeholders this sort of support, HETAS is very much involved with standards setting in the UK and Europe. Part of our role is to support installers, retailers, sweeps and manufacturers by encouraging safe, but pragmatic standards and Building Regulations guidance that is fit for purpose but not over burdensome on our industry and we hope you find 5the bulletins informative.

Find out more

Click here to access the HETAS Technical Area where you can download each of the bulletins and much more information exclusively available to HETAS Registered Installers, Approved Sweeps and Retailers. Detailed guidance can be found on the following topics:

  • Direct External Air Supply
  • Energy Labelling
  • Support Documentation – risk assessments | complaints | quotation templates
  • HSE guidance links
  • All of our monthly e-newsletters

If you have a technical question you can contact the helpline team on 01684 278194 or email

Copies of the new External Air Supply Commissioning Record can be purchased by installers in the HETAS Shop.

The articles produced as a result of conversations we have with registrants, training centres and inspectors, but we are always welcoming of suggestions on articles that would be of benefit to our registrants.

Click here to get in touch with the HETAS team.