There’s no one-size-fits-all when it comes to boiler installations. From fitting boilers in listing buildings or landlocked flats through to making space for an inspection hatch, installers will find that no two jobs are the same. Particularly complex jobs can quickly become a problem if you are restricted to just one type of boiler flue system, which is why it’s important to understand the benefits of a twin flue system.
What to Consider When Installing a Boiler
There are many elements that need to be considered during a boiler installation, including:
- Boiler position
- Flue termination
- Property regulations
Whether you’re fitting combi boilers or installing a new system in a stately home, we’ll take a look at these common stumbling blocks and how to overcome them when working on a complicated boiler installation.
What to Do If the Position of the Boiler Requires a Longer Flue Run
Some installations may require a longer flue run, for instance if the boiler placement is in the basement of the property. Historically, boilers were installed in kitchens across the UK. As many kitchens used to be situated in the basement of houses, the position of some boilers have remained within the basement even as refurbishments, room structures or heating systems have developed.
Basement boiler installations require a longer boiler flue to meet the requirements for flue termination. Rather than dealing with the additional work and cost of moving the boiler position, twin flue solutions can be used to provide the extra length without any of these hassles.
For example, Keston Boilers are able to run our flues up to 27 metres which allows for boilers to be positioned in locations that cannot be flued concentrically directly through an external wall - such as basement rooms.
Meeting BS 5440-1:2008 requirements
British Standard BS 5440-1:2008 details flueing requirements for boilers not exceeding 70kW. The main function of the flue termination is to ensure that the products of combustion are effectively discharged to the outside air in a safe location.
Main considerations regarding flue terminations are:
- Any termination needs to be positioned appropriately with respect to surrounding features on the building.
- Flue terminations should be designed to prevent any debris getting into the system that could have an effect on the performance.
- Relevant details outlined within the boiler manufacturers’ installation guides should ensure the safe operation of the appliance and prevent the position of the flue causing detriment to others.
There are other elements that need to be considered in addition to the BS 5440-1: 2008. All flues need to be adequately supported. All joints must be made and sealed with solvent cement suitable for the manufacturer-approved muPVC (PVC-C) flues conforming to BS 6209.
You Don’t Have to Rely on Parallel Flue Runs
The vast majority of domestic boilers are designed with a concentric flue system where the air supply and flue gases are managed within one flue. They are designed as a duct within a duct, with the exhaust gases taken away through the inner duct and the combustion air drawn in through the outer duct. Installations that use a concentric flue system can be installed vertically when leaving through the roof, or horizontally leaving through a wall.
Twin flue boiler systems will perform the same task as concentric systems; however, they do allow further flexibility in distance. In a twin flue installation, the air intake and exhaust flue run separately rather than within one another. This means the twin flue runs are not restricted to run parallel, so the air position will not be limited by the same restrictions placed on the termination of the combustion flue. Combustion gas pipe can therefore run further to the desired termination point while the air pipe can run through the nearest external wall next to the boiler.
For installers, using a twin flue boiler system will allow for greater flexibility and solve a common issue if the boiler is in a position that restricts the flue system to run parallel. The maximum combined length for both flues on a twin flue boiler like the Keston System S30 is 27 metres in total. For example, the air flue can be terminated three metres away from the boiler allowing the remaining 24 metres left for the exhaust flue run.
How to Install a Boiler If It Can’t Be Fitted on an External Wall
Boilers in domestic homes will be fitted on an external wall so the flue can be simply directed outside. However, properties such as landlocked flats lack sufficient external wall space for the flue termination to be placed. For example, there may be a balcony or windows near where the flue termination would normally be. This means a longer flue will be needed to extend towards the roof for the combustion gases.
In these instances, twin flue systems could be used to benefit the installation as the air intake and exhaust flue are not bound together and can be run separately either horizontally or vertically.
What is a Flue Inspection Hatch?
Where boilers are located away from an external wall, the flues are likely to run through the ceiling or wall voids. When using a twin flue system there are additional considerations to take into account such as the Corgi/Gas Safe technical bulletin TB200/TB008 regarding flues in voids.
To ensure safety checks can be completed, inspection hatches are required to be installed at appropriate points along the flue runs. The inspection hatches are intended to allow visual inspection of the concealed system rather than having full physical access. To ensure flues can be examined thoroughly, inspection hatches should be 300mm by 300mm in size and no flue joint within the void should be more than 1.5m away from the edge of the nearest inspection hatch. Making space for these hatches may mean additional remedial work will need to be done, such as added plastering after the hatches have been completed. However, safety should always come first and it’s vital you install a flue access panel to ensure the appliance doesn’t get classified as 'At Risk' if a Gas Safe registered engineer cannot view the flue.
Overcoming Additional Legislation and Property Regulations Affecting the Flue Run
There are certain properties that have additional legislation to consider regarding flue runs, such as listed buildings. There are over 500,000 such properties in the UK which are protected so that they are preserved for future generations. Amongst many other regulations, there are some that would affect the flue run.
For example, some regulations state that flues cannot be positioned in front of the property or any part that would be seen from a highway. This means that a more flexible flue solution will be needed to meet the requirements.
Cost-Effective Twin Flue Boiler Installations
There are a number of advantages to using a twin flue boiler system. Ultimately, the preferred outcome for the customer is cost savings, across both gas bills and installation. Twin flue boiler installations are a great option. They require manufacturer approved, small diameter (50mm) muPVC (PVC-C) solvent weld pipes - one for the air duct and one for the combustion gases. This solvent weld pipe is sold at a fraction of the price when compared to proprietary concentric flue systems, which makes twin flue boilers a particularly cost-effective option.
Retrofitting existing twin flue installations with longer flue runs is a more efficient and cheaper solution compared to moving a boiler to fit a concentric flue. If the original boiler position is within an area that does not have straight access to an external wall, you don’t need to consider moving the boiler, gas and water pipework and flue runs to suit a concentric system. Simply install a twin flue solution instead.
Completing Complicated Domestic and Commercial Installations
There are many types of installations that would reap the benefits of twin flue systems, particularly buildings that require a longer-than-average flue length. Twin flue systems are more cost and time effective for these boiler positions than concentric systems, while also complying with flue termination regulations. They offer a unique resolution for installers with tricky heating solutions.
British built since 2013, our twin flue boilers offer heating solutions without compromise for both domestic and commercial installations. Find out more about Keston Boilers or check out our news hub for the latest heating installation advice.
Our original advice piece offering solutions for complicated installations first appeared in Professional Heating & Plumbing Installer, October 2019 - why not check it out?