The SIL150T from Envirovent is definitely one of the quietest 6" Axial kitchen fan available. Unlike most other "silent" fans available Envirovent's kitchen fans retain an extremely high level extraction rate of 280m2/hr per hour while whispering away at only 32dB(A). It also features an IPX5 ingress protection rating which means it can be used in any zone of the bathroom.
The SIL150HT model has an internal timer which is simple to adjust between 2 & 25 minutes. It also features humidistat that detects when moisture is present in a room and will trigger the fan to run to the moisture is removed.
Specification
Air Extraction : Max 280m3/hr - 78 L/s
Noise : Max 32dB(A)
Watts : Max 29w
IP Rating : IP45
Dimensions
Width: 214mm
Height: 214mm
Spigot Depth: 89mm
Spigot Diameter : 147mm