How to choose ventilation fans
A ventilation fan buying guide
Many different types of fans are available to meet a variety of needs. Box fans sit on the ground and move air around a room. Window fans are used in windows to transport air from outside and circulate it throughout the area. Ventilation fans are used to move moist air from an area inside and transport it outside. Ventilation fans can be used in the kitchen, bathroom or other areas of the home. Providing adequate ventilation affects the heating, cooling and air quality of the ventilated area. As with any home improvement project, it is important to insure you have the correct home improvement tools available before you begin. But when thinking about how to buy a ventilation fan, there are a few points you will want to keep in mind.
>> Consider ventilation fan type
The first consideration to be made when deciding how to choose ventilation fans is to decide on the best type of ventilation fan for your project. There are four main types of exhaust fans that are available on the market.
- Ceiling mounted fans connect to the air ducts through a hole in the ceiling. The front of the fan is then attached to the ceiling itself.
- Wall mounted fans connect to the air ducts through a hole in the wall. Controls, settings and vents are accessible at the wall panel.
- Inline ventilation fans are located between or inside parts of the air ducts. Because they are located in the wall and not directly in the bathroom or kitchen, they are typically quieter than other fans and are able to allow a broad range of ventilation fan designs, including offering unobtrusive design details.
- Combination fans incorporate elements of different fan types or features into the ventilation fan. For example, combination fans may incorporate a heater into the system. Combination fans enable a wide range of options that are unavailable when only one fan type is used. By offering a combination approach to ventilation fan design, a larger powered ventilation fan can be utilized. Deciding which type of ventilation fan you need is the first step to answering how to choose ventilation fans that are right for you.
>> Consider airflow capacity
When deciding how to choose ventilation fans, another primary consideration is airflow capacity. Airflow capacity is related to the ventilation fan size. Airflow capacity is determined by the cubic feet per minute (CFM) the fan can circulate. The lower the CFM, the longer it will take the ventilation fan to circulate the air in the room. Generally speaking, larger fans have a higher CFM.
There is a 100 square foot rule that applies to small spaces. The 100 square foot rule states that bathroom exhaust fans or other ventilation fans used in spaces under 100 square feet require one CFM per square foot. This allows a quick and easy calculation of how many CFMs are needed for the ventilation fan.
In bathrooms, several other factors can affect the CFM needed. For each shower, tub or combination shower and tub, you should add 50 CFM. A whirlpool in the room adds 100 CFM. By making these adjustments when you shop for ventilation fans, you are better able to choose the best ventilation fan to meet your specific needs. Determining the airflow capacity your space requires is another step in how to a choose the ventilation fan that's best suited for you.
>> Equivalent duct length
Another factor that can affect the ventilation fan's effectiveness is the composition and length of the ventilation ducts. The length and composition of the ducts affects the pressure in the ducts and the force that the ventilation fan must overcome.
Ventilation ducts are built from many types of metal. Smooth metal ducts have a pressure that is equal to the length of the duct. Flexible aluminum ducts create more effective pressure than smooth metal ducts. Therefore, when calculating duct pressure, take the length of the flexible aluminum duct and multiply it by 1.5. Insulated flex ducts have even more pressure than flexible aluminum ducts. To calculate the duct pressure in insulated aluminum ducts, multiply the duct length by 2. Finally, elbows and caps create more pressure on the ventilation system. Add 15 feet for each 4-inch elbow or cap and 20 feet for each 6-inch elbow or cap. By calculating the equivalent duct length, you are best able to determine the pressure the ventilation fan must overcome when moving air from a moisture ridden environment to the outside. Remember this when you are learning how to choose ventilation fans. If your equivalent duct length is more than double your actual duct length, you'll likely need to go up another 50 CFM. If it's more than four times your actual duct length, consider going up a total of 100 CFM.
>> Consider ventilation fan features
Finally, it is important to consider additional ventilation fan features when deciding how to choose ventilation fans. Ventilation fans offer features that add to their value. Many ventilation fan brands include lights, heaters, timers and more in their ventilation fan designs. Including a light in the ventilation fan design allows the fan to serve an additional function and can even replace traditional light fixtures. Including a heater in the ventilation fan design improves temperature control and can warm the room as well as moving moisture rich air outside. Finally, including a timer in the ventilation fan design allows for self-shutoff capabilities, which helps to decrease energy use in the home.
Type of fan
|Ceiling mounted || |
- Single-speed: 50-110 CFM
- Multi-speed: 80-110 CFM
- High-capacity: 100+ CFM
|Decorative, recessed, hidden features, may be combined with timer, lighting, motion sensors, heaters and more |
|Wall mounted ||50-110 CFM ||Looks like other vents in the home, limited additional features, can combine with heater, lighting, timers and more |
|Inline ||100-500 CFM ||Hidden, quiet, can offer capacity ranges unavailable in other types, limited availability of features due to placement |
|Combo ||50-500 CFM ||Offers the largest variety of features at the highest capacity |