Air-exhaust system, LAS

In the case of an air-flue gas system or air-flue chimney, the cool supply air and the warm exhaust gas of a heating system are routed directly past each other so that the exhaust heat preheats the supply air in the chimney that is sucked in via the roof. In this way, the flue gas temperature when exiting the chimney is reduced, while the temperature of the supply air for combustion in the boiler increases. The primary purpose of this system is to save energy through heat recovery.

In addition, LAS technology always stands for room-air-independent operation of the heating system. To prevent the exhaust gases from being sucked back into the system via the roof, the exhaust air outlet is located well above the intake opening for the fresh air. The air-exhaust system is in principle suitable for the combustion of all types of fuels of all temperature ranges. Especially for condensing boilers that are fired with natural gas, the LAS system is state-of-the-art today.

There are basically two construction methods:

• pipe-in-pipe construction via double-walled pipes, which transport the hot exhaust air upwards in the inner pipe and the cool supply air downwards in the outer pipe. The large-area contact of the concentrically mounted tubes around each other ensures efficient heat exchange.
• Pipe in the brick chimney: The flue pipe is located in the middle of the chimney via spacers. The remaining airspace is used for the supply air supply. This construction method is used in particular for chimney renovations.

Principle of the air-exhaust system:

Source: bauwion