A question that comes up often is if flex ducting can be used to exhaust a fan. The simple answer is yes, but it is a little more complicated than that. Let’s take a look at some of the pros and cons of flex ducting:
PRO – Easier to Install
There is no doubt about it, flex ducting is a lot easier to install than rigid ducting. With rigid ducting, you have to plan out the system and account for elbows as well as needing to bind the ducting together with tape or adhesive. Flex ducting allows you to run one continuous line right to the wall or roof cap without much thought.
PRO – Easier for Room Level Installations
When installing an exhaust fan in a location that does not have attic assess, using flex ducting is an almost must. It allows you to make the connection to the fan’s duct collar without needing to cut a larger opening (and then repairing) in the ceiling.
PRO – Cost Effective
Generally, it will be less expensive to use flex ducting over rigid ducting, especially when you add in the extra labor involved.
CON – Lower Performance
When using flex ducting, one of the biggest issues is reduction in performance of the exhaust fan. The ducting will reduce the airflow and increase the sound level. The issue comes from the ridges in the ducting. Air gets “trapped” in them and causes a higher static pressure (read our earlier post here regarding static pressure to learn more). Higher static pressure causes the motor to work harder, which causes it to run less efficiently and louder.
CON – Not Meeting Specifications
This is a continuation of the lower performance. In situations where a specific airflow (CFM) is required, the lower performance from the ducting could cause the fan to fail inspection. For instance, if you have a fan that you expect to perform at 50 CFM but you are using flexible ducting, it might only produce 40 to 45 CFM. That might put you below the required airflow and cause the fan to fail.
CON – Less Durable
Typically, flexible ducting is constructed of either thin plastic or thin aluminum. Both will deteriorate over time or are very easily punctured. Rigid ducting is either going to be PVC plastic or thicker wall metal and should last a lifetime.
While using flexible ducting has a time and place, we do not recommend it in situations where rigid ducting can be used. Rigid ducting will almost always provide, better ducting, better performance and longer life. To learn more about Air King exhaust fans, visit airkinglimited.com. Also, read through our many blog posts regarding ducting, static pressure and choosing exhaust fans.
