Dual-speed and multi-speed exhaust fans may sound like terms that can be used interchangeably, but there are distinct differences between the two. Let’s take a look at each.
Dual Speed Exhaust Fan
A dual-speed exhaust fan will have two speeds – a low speed and a high speed, which may be referred to as a boost speed. A dual-speed fan will operate continuously on the low speed, so it will always be running. In times when more ventilation is needed, it will boost to high speed. This can be accomplished via a wall switch, a motion sensor, or a humidity sensor.
Why does it need to operate continuously?
Building codes (known as ASHRAE 62.2) in the United States call for a continuously operating exhaust fan to ensure proper ventilation of the home, increasing the indoor air quality. A convenient way to solve this code is to have a dual-speed exhaust fan. This allows the builder to only have to install one fan that solves for both the bathroom ventilation and the continuous ventilation.
How It Works
A dual is typically installed in a main bathroom and has a very low sound level. In most cases, you might not even hear it running. This is important for a continuously running fan since it will be running all the time. When the bathroom is being used, the fan will switch to high speed. This might be triggered by a wall switch, a motion or humidity sensor/switch in the fan, or mounted on the wall. Once the room is unoccupied, the fan will return to the low speed.
Multi-Speed Exhaust Fans
Multi-speed exhaust fans are different from dual-speed exhaust fans in that they only have one operational speed that is selected from two or more options. On a multi-speed fan, there is a speed selector integrated into the fan where the end user chooses which speed is desired or is needed for the space. The speed can sometimes be set at a specific number, or it could be a variable speed dial that you increase or decrease.
Why Would You Use It?
Multi-speed fans are primarily used in new construction, where the ventilation amount might need to be adjusted on-site. When you see a CFM rating, this is a test lab certification. The testing labs do a great job of testing as close as they can to the real world, but it can sometimes be different. The ducting might be a little different; there is an extra bend, a different wall cap is being used, and so forth (see our blog on static pressure). A room might require 80 CFM of ventilation. If an 80 CFM exhaust fan was installed, but is only delivering 70 CFM, there is a problem, and more than likely the installer will need to remove the fan and replace it with a larger one. If you have a multi-speed exhaust fan, all the installer has to do is adjust the speed to the higher CFM, and all is well.
The main difference between a dual-speed fan and a multi-speed fan is the number of active speeds operating. A dual-speed fan will have two, while a multi-speed fan will have one. Both provide excellent ventilation and increase the indoor air quality of your home. To learn more about Air King’s dual speed and multi speed options, including the newly introduced SF5810 three-speed slim-mount exhaust fan, visit airkinglimited.com.






