Round the bend
HETAS receive on occasion 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.
Recently this has included provisions surrounding immediate bends directly off the top of an appliance.
In instances where the general guidelines stated within Approved Document J cannot be followed as a means of meeting compliance with the Building Regulations, then page 40 of ADJ also permits for an alternative approach to be used based on requirements given within recognised BSI standards, to achieve a level of performance equivalent to that obtained by following the guidance within ADJ. For solid fuel appliance installations, the caveats within the following standards can be used;
- BS EN 15287-1 Design, Installation & Commissioning of chimneys for non-room-sealed heating appliances
- 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. This is certainly the case in situations relating to immediate bends directly from the top of an appliance, in particular when trying to appropriately align the outlet/spigot of an appliance and connect to an appropriate chimney system above.
Up until recently, the minimum distance from the top of the appliance to the first bend of connecting pipe was a minimum distance of 600mm as prescribed with BS 8303:1994 Installation of domestic heating and cooking appliances burning wood and solid fuel mineral fuels – specification. More recently however, British Standard 8303:2018 has been revised and updated regarding this application and clause 11.4.2 of BS 8303 now allows for the following bend configuration directly off the top of the appliance;
There shall be a minimum vertical length of connecting flue pipe/chimney of 600mm directly above the top flue outlet to create laminar flow of the exhaust gases and reduce the deposition of soot and tar. An offset directly on top of the appliance made up of two bends and offsetting not more than half the diameter of the connecting flue pipe is permitted to align the appliance exit with the chimney. The offset should be as shallow as possible, ideally using two 15-degree bends. However, where height is limited above the appliance, an offset with bends up to the maximum 45 degrees can be used.
If the above caveats are met, then the configuration can be used, as long as the installation is appropriately commissioned, and a flue draught reading is taken and is confirmed to meet with the appliance manufacturers required flue draught tolerances stated within their installation instructions.
The HETAS Technical Helpline is available for HETAS registrants. If you have any technical questions or would like to discuss this article further please contact the team.