Boiler/chimney flue locations

> Basement areas, retaining walls and light wells

Chimney outlets shall be sited so as not to discharge within the curtilage or confines of any basement area, light well or external space formed by a retaining wall or passage unless provision is made to ensure the safe disposal of the flue gases, as follows:

• Chimney outlets from roomsealed appliances and fanneddraught non room-sealed appliances may be sited in such areas provided that they are not sited more than 1m below the top level of the basement area, light well or retaining wall.

• Chimney outlets from roomsealed appliances and fanneddraught non room-sealed appliances may be sited in a basement area or light well where this is formed by a single retaining wall that creates an uncovered passageway at least 1.5m wide. This shall only be done if the passageway allows free air circulation beyond and around the ends of the structure and the retaining wall, if the passageway terminates above or at ground level, and if unobstructed air movement can take place at the open ends of the passageway.

Termination into a car port

Some appliance manufacturers do not permit the termination of a condensing boiler chimney/flue within a car port. Others do but specify that the guidance in BS 5440-1:2008 must be followed.

This guidance sets out that when a terminal is to be sited in a car port or building extension, the following additional recommendations apply:

• The car port or add-on extension must have at least two open and unobstructed sides.

• The distance measured vertically above the terminal to the underside of the balcony or car port roof should be at least 600mm for natural-draught balanced flue, and 200mm for a fanned-draught room-sealed flue.

• If there are any openings under the car port that communicate with the inside of the property, such as opening doors, windows, or air bricks, the distance from these should be no less than 1200mm.

• If the roof is made from a plastic material, the installation should be treated with great care due to there being no simple method of protecting the roof against potential heat damage.

Common situations

The chimney/flue is not sealed to the wall or has been sealed with incorrect materials

The appliance chimney/flue must be sealed to the building fabric internally and externally in accordance with the manufacturer’s instructions. Any material other than mortar used for this purpose must be confirmed as acceptable by the appliance and sealant manufacturer. Refer to Technical Bulletin 152

The horizontal flue pipe protruding from the wall has not been cut to the specified length

This issue is encountered almost every day. Only the boiler manufacturer can confirm whether the method of termination is acceptable or not. There will generally be more specific guidance in the MIs about whether the installation is acceptable.

The flue is incorrectly supported or not screwed when required

The appliance chimney/flue must be assembled and installed in accordance with the boiler installation manual. If it is not supported correctly or screwed when required, complete a risk assessment to determine the relevant risk classification to apply. In some instances, it may be deemed to be “Not in Accordance with MIs”.

Terminal clearances to boundaries and re-entry points to the property

The appliance chimney/flue must be assembled and installed in accordance with the boiler installation manual. This should contain the information you need to ensure that the flue termination is safe.

Openable windows and doors

Where the flue termination is positioned diagonally from an opening door, window or air vent and the required distance is not specified in the manufacturer’s instructions or BS 5440-1:2008, you must contact the appliance manufacturer for guidance, preferably in writing.

For a vertical flue termination positioned where there is an opening window or door located on an adjacent wall and the required distance is not specified in the manufacturer’s instructions or BS 5440-1:2008, contact the appliance manufacturer for guidance, preferably in writing.

However, if this information is not in the manual, you should contact the manufacturer’s technical helpline. If they can’t help, they may recommend referencing BS 5440-1: 2008. This advises that a minimum distance of 300mm should be applied from re-entry points such as opening windows and doors. A distance of 300mm is required from a boundary line adjacent to the chimney/flue termination or 600mm from a boundary opposite the terminal.

The standard also recommends not to terminate directly across a boundary line, regardless of how far away from the boundary it is. This should prevent nuisance pluming on to neighbouring patios, etc (see previous page).

You can send the manufacturer’s response to Gas Safe Register to save to your business notes for future reference.

All vertical flue installations must be completed in accordance with the appliance manufacturer’s installation instructions. The system must be adequately supported throughout its entire length at the distances specified by the manufacturer and using manufacturer-specified support brackets. ■