Understanding Boiler Flue Regulations

Abiding by boiler flue regulations helps to keep both you and your customers safe. Regulations are put in place to prevent harm by ensuring boilers are installed correctly. It’s therefore vital that gas engineers have a comprehensive understanding of boiler flue and gas safety regulations to make sure they don’t fall foul of the law.

What Are Boiler Flue Regulations?

Boiler flue regulations determine how boiler flues should be installed safely. Condensing gas boilers produce waste gases that are transported out of the boiler and safely dispersed outside of a home or property via the flue.

These waste gases can be very harmful, and a slight error in flue positioning or installation could be catastrophic, which is why strict guidance and legislation has been put into place. Gas Safe registered engineers are required by law to follow the boiler installation manual.

Most people will be familiar with boiler flues. It is a piece of pipework, fitted through an external wall, which expels waste gases. Boiler flues can’t just be fitted anywhere on any old wall, though. It must be positioned according to regulation so it doesn’t negatively impact the building’s occupants, neighbouring properties or passersby.

Gas Boiler Flue Position Regulations

When it comes to positioning a boiler flue, there are many considerations installers must take into account. These requirements ensure boiler waste gases don’t compromise safety, cause a nuisance or damage property.

Some key points to bear in mind for fanned draughted domestic boiler flue installations:

  1. The boiler flue terminal should be positioned away from doors, windows or other openings. There should be a space of at least 300mm above, below or to the side of any opening. Harmful gases should be properly expelled from the property, so they cannot re-enter. Flue terminals should also typically be sited at least 600mm above flat roofs.
  2. Boiler flues should be positioned at least 75mm below any material that could be damaged by heat, such as guttering. They should also be at least 150mm to the side of vertical drain or soil pipes. The waste gases expelled from the flue can be extremely hot, which could cause external damage.
  3. Waste gases can be dangerous if they are breathed in and the plume from condensing appliances can cause a nuisance if the terminal is not properly positioned, so avoid positioning the boiler flue where it would discharge onto public spaces like pavements wherever possible. Keep the flue at least 2m off the ground.
  4. If it isn’t possible to keep the flue over 2m off the ground, you must install a terminal guard. It should provide at least 50mm clearance from the flue terminal to ensure passersby won’t get burned accidentally.
  5. A boiler flue cannot be routed through another property. It can, however, be routed through a community area as long as access is always available.
  6. Condensing boilers produce a plume from the flue terminal — and it’s against regulation for it to cause a nuisance. To avoid an issue, ensure the plume doesn’t cross a frequently used area, public route or neighbouring property. You should also make sure that the flue terminal and the plume produced won’t trigger infrared security lighting or obscure any security cameras.
  7. If your boiler flue is positioned horizontally, angle it slightly upwards. Dripping water vapour could be harmful so it’s important this drains back into the boiler rather than onto the exterior of the property or, worse, anyone who happens to be walking past.
  8. Don’t conceal your flue! Boarding over or encasing a boiler flue, particularly vertical ones, might look a little better but you must always ensure you don’t cover up access points or joints in the flue. A flue’s predominant job is to expel waste gases, so it should not be obstructed.
  9. Install inspection hatches if your flue is positioned so it cannot be physically accessed. An engineer should be able to visually inspect your boiler flue joints — and may classify it as ‘At Risk’ if they can’t.
  10. The Gas Safe technical bulletin TB008 provides guidance on meeting regulation when it comes to flues in voids. Boilers may run through ceiling, floor or wall voids if they are located away from an external wall. Inspection hatches should be installed at 1.5m intervals along the flue run to allow for physical access and examination. These hatches should be 300mm by 300mm in size.

In addition to wider regulation and legislation, it’s important to follow the individual boiler manufacturers’ installation guides meticulously to ensure safe handling and operation of the boiler flue.

Flue Support Regulations

Guidance states that installed flues must be supported throughout their entire length to ensure the flue-run doesn’t dip. This could lead to issues such as an accumulation of condensation, which may impact the boiler’s performance.

Make sure your flue is firmly secured using bolts or screws - no one wants a loose flue, after all. Aside from manufacturer-approved push-on or plastic compression connectors, all joints must be made and sealed with solvent cement thus conforming to BS 6209 regulation.

A qualified Gas Safe registered engineer will ensure your flue is safely fitted during your boiler service, so you don’t need to worry about fixtures becoming loose over time.

Do Boiler Flue Regulations Only Apply to New Installations?

Some of the more recent regulations may only apply to new boiler installations. For example, if you’re looking to replace an old boiler (particularly one that was installed before 2005), it’s likely you’ll need to replace your boiler flue too. However, there may be cases where you’ll need to modify your existing boiler flue set-up to comply.

All newly installed boilers must be condensing boilers, so if you’re upgrading or replacing a boiler they will need to be a condensing boiler and the flue system must be suitable for that type of boiler. To comply with Boiler Plus Regulations any new domestic or commercial boiler must have an Energy Rated Performance (ErP) rating of at least 92%. This system makes boilers more efficient as it captures and re-uses heat energy.

Building Regulations (Amendment) 2018 updates have caused a particular issue for landlords or property owners of high rise flats or apartments. The update in legislation states that any material used in external walls of high-rise residential buildings should be fire resistant and should not contain combustible materials, including plastic flue components.

The interim solution suggests that these plastic flue components can still be considered in particular cases under section 8 of the Building Act, though it is still important all installers, property owners and landlords are aware of these regulations to ensure new boiler flue installations remain compliant.

Different Types of Boiler Flue

Practically every boiler is fitted with a flue including heat, combi and system boilers such as Keston’s System S30. There are two main types of flue systems: concentric systems and twin boiler flue systems. Twin boiler flues offer additional flexibility, ensuring installers can meet regulatory requirements.

In more complicated installations some boilers cannot be flued directly through an external wall and may need to be fitted vertically through the roof. It’s worth noting that some flues may only be permitted to travel a certain distance and, for every bend used in the flue, the length it can travel is reduced by one metre.

If a longer flue is needed, a twin flue boiler system could be the best option. In a twin flue installation the flues are not restricted by the need to run parallel, so the combustion gas pipe can run to a termination point much further away than your air intake.

In some cases, a twin flue boiler installation ensures you’re able to meet boiler flue regulations. For example, if you were planning to move a boiler to a position where the most convenient termination point would be too close to a window, you could be able to overcome the issue using a twin flue system.

Twin flue boilers are also perhaps the most suitable option for listed buildings. Many of these buildings are protected by regulations, some of which impact the positioning of the flue run. For instance, flues cannot be positioned in front of the listed building or any part of the property that could be seen from a highway. In these cases, the flexibility of a twin flue run could help to meet specific requirements.

Domestic Boiler Flue Regulations vs Commercial Boiler Flue Regulations

Some larger domestic or commercial properties require boilers over 70kW in size, or two or more boilers such as Keston Heat 2, to adequately heat the building. Using two or more boilers on a cascade system offers great flexibility for commercial installations as higher outputs are possible when frame and header kits are used.

Both domestic and commercial boiler flue installations should comply with Building Regulations Part J legislation, but there are some additional elements to consider when it comes to commercial installations.

As with domestic boiler flues, commercial flues should be CE certified for safety and performance. Commercial flues also need to be supported properly and firmly secured, with an inspection hatch installed if necessary.

In terms of positioning, commercial flues, including those on a cascade system, should:

  • Be fitted straight
  • Be placed away from materials that could become heat damaged.
  • Have an appropriate discharge height, calculated to ensure exhaled waste gases do not cause harm to the public or nearby properties.
  • Once fitted, be pressure tested to make sure there are no leaks or installation issues.

Who Can Work With Boiler Flues?

As most people know, only Gas Safe registered engineers can work with domestic boilers and boiler flues. They are trained to understand and recognise the latest boiler flue regulations and how this relates to individual properties. As with all building regulations, rules and requirements change over time, and keeping abreast of the latest changes is key.

Gas Safe registered engineers must notify work on all gas appliances via the Gas Safe Register, APHC or boiler manufacturer. This is to ensure that installations are recorded, and property owners are provided with a Building Regulations Certificate of Compliance (England & Wales).

Complying With Boiler Flue Regulations

Boiler flue regulations aren’t just there for show and failing to comply with them carries significant consequences. Of course, the biggest repercussion of not complying with regulations is causing serious harm or catastrophe. However, installers could also face sanctions for failing to comply even if the problem was spotted before any damage was caused.

Remember — boiler flue regulations are a type of building regulation, and as such both property owners and gas engineers must comply. Local authorities regulate and enforce building regulations, but the Gas Safe Register may also investigate installation issues. Failure to comply with guidance and legislation could result in financial penalties or prosecution.

Keep Up to Date With Flue Regulations

Building regulations change regularly. They are often updated to improve safety or environmental issues. The main documents to read up on include: Building Regulations Part J, British Standards BS 5440-1:2008 and the Guide to the Condensing Boiler Installation Assessment Procedure for Dwellings (ODPM 2005).

Primary regulations around the installations of commercial flues include Building Regulations Part J, the Clean Air Act (1956 Amendment), the IGEM/UP/10 Edition 4 and the British Standards BS 6644:2011 and BS 5440.

Keep an eye on the latest boiler regulations so you know what’s in the pipeline, making sure you can plan ahead and select the right boiler and flue system for the job. For the latest news and information, bookmark the Keston blog.