Fumus 2 is always equipped with a fan in the lower part of the chimney. This fan pushes the fresh air drawn in by the chimney through the fresh air distributor and into the house. The amount of air entering the barn is regulated by means of a butterfly valve above the fan. Depending on the position of the butterfly valve, anywhere between 100 percent fresh air (vertical position) and 100 percent recirculating air (horizontal position) enter the barn. Between these positions, a certain amount of fresh air is mixed with the house air, which is drawn in through the 10 cm wide opening at the chimney. This means that, depending on the ventilation requirements, the barn can be supplied with fresh air, mixed air or recirculating air. In case of minimum ventilation (during cold weather) Fumus 2 can also be operated with balanced pressure or slight positive pressure. Fumus 2 is available with the following diameters: 650, 730, 820, 920mm.