Can I connect my new condensing boiler to a collective chimney?

Do you live in an apartment and plan to replace your old individual boiler with a new condensing model? Caution: for connection, some precautions are required in order to avoid any danger and to comply with the regulations on appliances connected to a collective duct.

In addition, connecting a new condensing boiler to a collective chimney is not technically simple. This problem also requires a collective response and the involvement of all the occupants of the building.

Mixed connection = danger!

Several problems can arise when connecting a new condensing boiler to an old collective flue:

• most old fireplaces are not suited to the latest generation of boilers.The material they are constructed from would not be able to withstand the acidic condensates and moisture that are normally deposited in the duct;
• new boilers are more efficient and emit much less hot smoke. They therefore have less draw and are equipped with an exhaust fan. Old appliances do not need a fan: hot fumes rise more easily. Therefore, connecting different devices (conventional and recent) on the same conduit can cause damp and condensation problems, and even a backflow of burnt gases to neighbouring apartments. Watch out for the risk of CO poisoning!
• regulations forbid these mixed connections.

What's the solution? Ask a specialist!

There's no question of 'tinkering' to arrive at an approximate solution: we're talking about the safety of all occupants of the building. Only an expert who is properly specialised in these issues can take into account all the technical aspects of the problem. Not all heating engineers have this expertise and the best thing to do is refer to a specialist consultancy.

After examining the flue and the installation of other appliances, an experienced professional may propose:

• adapting the flue for collective smoke (e.g. installation of casing, addition of an extractor)
• creating a specific new flue
• connecting the new device to an independent outlet, possibly in an external wall if the town planning department authorises this or if the proximity of a window or a balcony does not make it impossible.

To determine what is possible, it would be ideal to carry out a duct inspection by camera. This will also often be the opportunity to discover unknown problems (interior collapses, various objects, air conditioning pipes crossing the flue, kitchen hood or dryer connections, etc.).

Good to know: in Brussels there's a grant for chimney intubation

Coordinate with your neighbours!

Upgrading your heating system is a good idea! However, it is much easier when all the occupants of a building coordinate to make this change at the same time. In this case, you simply adapt the duct of the collective chimney and at the same time replace all the devices connected to it.

Your neighbours aren't all ready to take the plunge? Two solutions can be considered:

1. Create a new, suitable duct in addition to the existing chimney which everyone can gradually connect up to. This solution is not feasible in all cases, however.
2. Adapt the existing chimney to accommodate two evacuation pipes: one suitable for the old boilers and the other for new ones. This solution is only conceivable if the existing duct is in good condition and sufficiently large.

In any case, such a project must be submitted to the trustees and discussed between the co-owners. This naturally entails joint investments (note that in Brussels there's a grant for chimney intubation). But the reality is that this expenditure will be necessary sooner or later. The advantage is that after the change, the whole installation will be ecological and energy efficient, while meeting current safety requirements.

For additional details see 'Le remplacement des chaudières individuelles à brûleur atmosphérique raccordées à une cheminée collective existante', a bulletin by Bruxelles Environnement (only available in French and Dutch).