Using Flex Ducting with an Exhaust Fan

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.

Duct, Duct, Duct, Insulate - Insulating Your Ductwork

Have you ever taken a shower and the mirror starts to fog up? For almost all of us, we have experienced this at least one time in our life, probably more often than not. You might open a window, wipe it down with a towel, or think to yourself that you need a better exhaust fan (Air King can help with that!). What a lot of people don’t think about is that same steam that is causing your mirror to fog over is also going through your ducting. This presents a prime opportunity for condensation to form within your ducting. Condensation in the ducting forms when the hot steam from the shower passes through the cooler ducting, causing the steam (water vapor) to turn into a liquid form (water). This is especially true in cooler climates of the country. A very simple fix is to use insulated ducting as well as placing insulation around and on top of the actual exhaust fan (Make sure to check the rating of your exhaust fan as to how much insulation can be placed on top of it. Generally fans are rated for at least an R40 factor). By using insulated ducting it does not allow the air flowing through it to cool fast enough to cause condensation.

What is the big deal with condensation? Condensation can be harmful in many ways. Anytime you have sitting water, the potential for mold and bacteria growth exists, so you are working against one of the main reasons you have an exhaust fan in the first place. Another issue is depending on the situation you could cause enough condensation to form that it starts to drip out of your fan and possibly cause damage to the ceiling material around the fan.

Air King, as well as the Home Ventilation Institute and ENERGY STAR® all strongly recommend that insulated ducting be used with all exhaust fans, so take a minute and check to see if your fan’s ducting is insulated or not. Your fan’s ducting will thank you!

Want to learn more? Take a look at our other topics or click on the “Learning Center” tab of the Air King main website at www.airkinglimited.com.