Cascade Considerations: Exploring Flueing Options for Commercial Heating Systems

The installation of modern condensing boilers in a cascade arrangement is a popular choice for meeting a building’s heating and hot water demand efficiently in a variety of sectors. Andy Green, Technical Director at Potterton Commercial explains how heating engineers can overcome flueing challenges for these types of systems.

Heating systems installed in cascade are fast becoming the go-to choice for buildings with significant heat demand that need to deliver this heat efficiently and from a small plant room. While cascaded systems may offer a host of benefits, there are some additional considerations which need to be made to meet the flue requirements for these types of installations as opposed to single heating systems.

There are various options available for cascaded heating systems when it comes to flueing, with most flueing requirements often dependent on the output of a heating system.

One of the most important factors to consider is that the flueing options available need to match the flexibility of the cascaded heating system itself. For example, while it’s great that a series of boilers can be installed together in a tight plant room around a corner, the same is required of the flue which must also fit within the height of the plant room and bend around a corner if required. Another crucial factor to consider is any regulations and standards which need to be adhered to.

Legal requirements

The Clean Air Act stipulates a number of measures to reduce air pollution including certain flue requirements which must be followed such as whether vertical or horizontal flue termination is appropriate.

For installations where the termination is low level and horizontal, and the net heat input is between 150kW and 333kW, the local environmental health officer will have to grant permission to terminate at that position. However, for a cascade of boilers with a total net heat input exceeding 333kW, a vertical flue termination is required, terminating above a building and complying to chimney heights. These installations should also be assessed and signed off by the local authority or the local environmental health officer.

Another key piece of guidance is IGEM/UP/10 which sets out guidelines for the installation of a range of flued gas appliances. This covers the likes of ventilation, flue sizing and the height and location of flue terminations. Risk assessments can also be completed as part of the IGEM/UP/10 documentation, helping installers to gauge whether their installations are compliant or not.

Here to help

There are some flueing accessories which tend to be supplied as standard with most heating systems, such as plume kits which terminate either horizontally or vertically, and cascade non-return valves, to prevent the backflow of combustion products to boilers that aren’t firing. However, many boiler manufacturers will also offer a series of additional flueing accessories to help with the installation of cascaded heating systems in particular.

For example, if you have a cascade of boilers with a net heat input of over 333kW, then the flue will need to be run vertically to terminate above the building. In this scenario, cascade flue header kits are designed to help installers on their way to meeting this requirement. Flucade kits are often suitable for two to six boilers installed in a cascade and available in 150mm and 200mm diameters with extension pieces. These kits also include all associated components including a non-return valve.

For flues running externally, a common issue is that the very low outside temperatures we often experience in the middle of the winter can cause condensate to freeze. With condensate pipes forming an essential part of a boiler’s flue system, there is the risk of the boiler being unable to dispose of fumes if these pipes are blocked, meaning the boiler cannot operate safely. In addition, it isn’t uncommon to see the ingress of water into the fresh air supply in these conditions. Thankfully though, external flue kits prevent both of these scenarios from occurring.

Talk to the experts

There is a large amount of guidance for installers to navigate when it comes to the flueing requirements and options for commercial heating systems. As such, we would advise installers to seek the advice of a flue specialist when they’re approaching a cascade of flues to ensure the assembly is quick, safe and reliable. These specialists will be able to help with the design of a suitable flue system that is safe and compliant with all standards and regulations.

For more information on Potterton Commercial’s accessories and flue kits, please visit: