CLV systems
A CLV flue gas discharge system, also called Combination Air Supply-Combustion Gas Discharge System, can be found in apartment complexes or in other stacked residential buildings. In a CLV system, several boilers are connected to one common discharge pipe. This system combines air supply with a flue gas outlet, comparable to a concentric system (the pipe-in-pipe principle). Fresh air is drawn in from the roof through the outer pipe and the flue gases are blown out through the inner pipe to the roof.
CLV systems are used in new construction and renovation projects. For old apartment complexes it is possible to reuse an existing CLV system. A VR boiler must be replaced by an HR boiler. By using the special CLV renovation system MultiFlex from Burgerhout, the existing CLV system can be used for installing a new communal drainage pipe. This drain pipe is suitable for condensing heating appliances. The CLV renovation is a lot cheaper and causes less nuisance for the residents.
The CLV systems for VR boilers are based on the negative pressure principle. The boilers are connected to one common flue gas outlet. To prevent flue gases from one boiler not ending up in one of the other boilers, the CLV system must be designed in large diameters. CLV systems to which high-efficiency boilers are connected use the overpressure principle. Each HR boiler pushes the flue gases out of the central heating boiler by means of a fan. This makes it possible to work with smaller diameters. The overpressure principle requires that a non-return valve is installed in the boiler, this prevents flue gases from flowing back. The most modern central heating boilers are supplied with an integrated non-return valve. If this is not present, an external check valve must be used.
A half CLV system is a combined flue gas discharge system and does not have a combined air supply like the full CLV system. The combustion air supply is supplied individually via the facade or the shaft for each boiler. This system is common in renovation projects. A half CLV system is cheap and easy because it requires hardly any structural adjustments.




















