The Viessmann 7855596 Radial Fan (NRG118 B1HA/B1KA) is a high-performance fan assembly designed for use in Viessmann B1HA and B1KA boiler systems. It operates by generating consistent airflow to support optimal combustion and heat exchange efficiency. https://www.partshnc.com/7855596-viessmann-radial-fan-nrg118-b1hab1ka