Bathroom Exhaust Fans Need To Vent Outside
The purpose of these fans is to remove moisture from bathrooms while the shower or bath is in use. Venting that hot, humid air into the attic can cause severe moisture and mold issues.
This video shows the fans terminating right below the roof, which is better than if they terminated right above the ceiling; however, it’s still wrong!
The powered vent in the roof directly above these vents is not fully removing the bathroom moisture from the attic. If you think it’s “close enough,” I’d encourage you to use a portable fogger to familiarize yourself with the “capture zone” of fans and vents.
It’s shocking to observe the airflow near fans and vents – I think we all assume they work better than they actually do.
If the powered attic fan is rated for 1500 CFM (cubic feet per minute,) that does not necessarily mean it’s going to be pulling enough air from the entire attic, including the bathroom fans directly below.
If you used a portable fogger directly below it and moved it around to see how far away air is actually being pulled into the fan, you’d probably see fairly stagnant air a couple of feet away from it.
This means that the fan is not creating a steady flow of air from all around the fan. It’s continuously moving air directly next to it. Yes, that does help move air from further away. However, it’s far from guaranteed that it’s able to sufficiently ventilate the attic as well as pull sufficient air from the bathroom fans that terminate directly below it.
This is one of the reasons that proper attic ventilation is so important. Adding a couple of powered attic fans does not effectively cycle air through an attic. There should be a steady stream of airflow from the bottom areas of the attic to top, and all indoor vents (bathroom, kitchen, laundry room, etc.) should exit the roof.
If these indoor vents terminate in the attic, it disrupts the flow of air that is required to ventilate the attic, while also adding additional moisture which can cause large mold problems.
This attic also had improper attic ventilation, which makes the bathroom vent problem even more important to fix…but that’s going to be a future blog post.
If you live in Houston and want your attic ventilation checked, fill out the contact form below!