Heat Shielding Requirements
Back in the September Technical Bulletin, HETAS provided an update on the development status of the BS8303 standard for installation of domestic heating and cooking appliances burning wood and solid mineral fuels. HETAS was pleased to announce that on the 26th October 2018 the BS8303:2018 standard was officially published; this supersedes the requirements contained within the previous 1994 version.
The newly released standard contains some significant amendments, which HETAS will continue to inform registrants about through its Technical Bulletin publications and refresher training sessions. For the purposes of this article, the provisions surrounding the protection of combustible materials via an appropriate heat shield in freestanding configurations (not situated in an appliance recess) are covered, particularly in scenarios whereby the property in part is constructed of lightweight construction materials (i.e a timber stud inner leaf).
When can a heat shield installation requirements be applied?
In most cases, the heat shielding provisions will be applied in situations whereby the installer is limited for space and is unable to meet the appliance manufacturers required clearance distance to combustible materials stated within the appliance installation instructions.
Using an appropriate heat shield will allow for these distances to be reduced to those prescribed within the newly released BS8303 standard, and in doing so ensuring adequate protection to adjacent combustible materials is maintained at all time, in compliance with J4 Protection of Building, stipulated in the UK Building Regulations requirements.
Before commencing works using the prescribed shielding techniques, it is important to ensure that the installation design incorporates the use of a solid fuel appliance of suitable performance and also a heat shield manufactured from suitable materials. Under all circumstances, the following criteria shall at least be met:
- The appliance installed has a nominal heat output not exceeding 7kW, as referenced on the CE data plate or as referenced in the manufacturers installation instructions technical data
- The heat shield is manufactured from a minimum 1.5mm galvanized steel, and is appropriately affixed to the surrounding structure using non-combustible fixings
- In instances where the appliance manufacturer provides the heat shield, confirmation of clearances within the manufacturer’s installation instructions when using a heat shield shall be followed
The heat shield shall at all times remain open at both the top and the bottom to allow for a flow of cool air between the heat shield and the combustible materials it is installed to protect.
If the appliance selection criteria and heat shield construction caveats as stated above are met, then the clearance distances to combustible materials as stated by the appliance manufacturer can be reduced to a minimum distance of 95mm from the rear of the appliance to the front face of the heat shield when installed at 90° angle parallel to two internal walls. If the appliance installation is at an angle of 45° to each to each wall, then these distances may be reduced to no less that 65mm from the nearest point of the appliance to the front face of the heat shield as stated.
- An air gap of 25mm is maintained at all times between the rear face of the heat shield and front face of the protected combustible material
- Clearance distances from the size of the appliance to the front face of the appliance shield when installed in a 90° configuration is a minimum of 95mm
- The shield extends to at least the extremities of the hearth, and at least 300mm above the top surface of the appliance
- There shall be no protrusions above the shield to hinder flow of cool air behind (i.e shelves)
HETAS has created a series of diagrams to help visually illustrate required heat shielding clearances and other measurements. Click the images to download the guidance images.
For more information and guidance on the new heat shielding requirements prescribed within BS8303, HETAS registrants can contact the HETAS Technical Helpline on 01684 278194 (please have registration number to hand) or email firstname.lastname@example.org.