Hon&Guan’s WhisperAir S4 is a 4-inch silent mixed-flow inline duct fan designed for low-noise ventilation in compact duct runs. This variant ships without a plug and uses a durable PP housing with internal sound-absorbing silencer cotton. It is rated at 167 CFM, moving roughly 284 m³/h through 100 mm ducting, and carries IP44 protection. The operating temperature range is −20°C to 60°C, and optional modules include three-speed control, a timer, and temperature/humidity sensing. Brand specifications list about 38 W power on 100–120 V, a nominal 25 dB noise level, and approximately 2250 RPM. Typical uses include hydroponic grow tents and general exhaust where stable mixed-flow performance and quiet operation are important.