If you are in the process of choosing and researching a home exhaust fan, you will know that there are many technical aspects to consider: the size of the room, the number of air changes per hour, the extraction rate, part L of the Regulation of construction, the zoning of the bathroom system, duct length and resulting air pressure, IP rating, energy use… the list seems endless!
The decision to retrofit an extractor fan is often motivated by the need to expel steam from a bathroom or cooking odors from a kitchen and is made by the owner. When installing a fan in new construction, a real estate company or electrical contractor will install fans to comply with Part L of the building code. In both cases, the single most important factor is the air extraction rate: how much air is removed during a given period. This is expressed in cubic meters per hour (m3/hr) or liters per second (L/s).
However, one important consideration that is often overlooked by the homeowner, and understandably ignored by the third-party contractor, is the noise generated by the fan when it is running.
Most manufacturers indicate the noise level of their extractors in decibels dB(A) within the technical specification. Such information is now easily found on the websites of manufacturers, retailers, and wholesalers. Those fans that do not clearly display the dB(A) probably have something to hide and should be avoided.
So what is an acceptable noise level? To some extent this is subjective; what is good for some may be annoying for others. However, the installation and the type of fan have a great influence on this answer. Most kitchen fans are six-inch, meaning they use a six-inch impeller. (Unlike most bathroom fans that use a four-inch impeller.) consequently, a larger motor is required to drive it. There is simply no getting around the fact that a larger motor will result in a high decibel level. In fact, even the quietest six-inch fans are louder when running than the loudest four-inch ones. However, the kitchen is a room that can accommodate higher decibel levels. Why… well, think about how the fan is being used: The fan is almost certainly being used to extract odors from the kitchen. In this situation, the user and the other inhabitants of the property will be much less aware of the fan noise, being obscured by the sounds of food preparation.
However, four-inch fans are used at completely different times. Nighttime visits to the bathroom or toilet, for example, when the house is completely quiet, are much more audible. The opening and closing of a door, the creak of a floorboard, can all be heard in different parts of the house. In this situation, the fan noise is much more prominent. Until recently, this simply couldn’t be helped – engines were inherently loud. However, almost every manufacturer now makes either a specifically quiet fan or a range of quiet fans. While most normal four inch models run at around 30 – 40 dB(A), these quiet or silent models run at around 24 d(B)A. If the fan is installed correctly and not mounted on a wooden beam, they will remain quiet, even in the middle of the night.
More information on quiet fans is available at Fan World Fan.
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