Why Is My Bathroom Exhaust Fan Blowing Air Down?

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If your bathroom exhaust fan has been installed correctly and works fine, you’ll barely even remember that it exists. It’ll continually work in the background to keep your bathroom air clean and fresh. Unfortunately, some exhaust fans end up blowing air down instead of pulling it out!

Suppose your bathroom exhaust fan is blowing air down instead of pulling it out. If that’s the case, it could be that the fan blades or wiring were installed backward. It’s also possible that the backdraft flapper is stuck closed. Besides that, the vent duct might be undersized, blocked, or flattened.

If you’re facing the problem of an exhaust fan that’s blowing air down, you’ve come to the right place. Here, we’re going to explore all the possible reasons so that you’ll be able to resolve the issue quickly.

Keep on reading!

Fan Blades Installed Backwards

When installing a bathroom exhaust fan, the fan blades must be installed a certain way. In doing so, that’ll ensure that the fan will continually draw air and push it in the correct direction, taking it from your bathroom and making it through the vent pipe and out of your home.

Although the likelihood of this happening is relatively low, it’s still a rookie mistake that does occur from time to time. The installer may have put the fan blades in the wrong way.

As a result, when the fan blade spins, it draws air from the vent and pushes it down into your bathroom instead of the other way around.

The good news is that if this is indeed the cause of the problem, it’s a pretty easy and straightforward fix. All that’s needed is for the fan blades to be reinstalled the correct way, which will solve the problem! Doing that will ensure that the air flows in the right direction for the exhaust fan to affect your bathroom’s air quality positively.

Fan Wiring Installed The Wrong Way

Here’s another possibility. On some fan motors, installing the fan wiring incorrectly could cause it to turn the blades the wrong way around. So, rather than spinning the fan blades to pull air out of the bathroom, it ends up doing the complete opposite and pushing air down instead.

Bear in mind that this doesn’t happen for all types of exhaust fan motors, so the likelihood is relatively low. Still, it is a very real possibility.

Much like what was mentioned in the previous section, this is also a problem that’s easy to fix. Of course, you’ll want to leave any electrical work to a qualified technician. Plus, if the installer is the one who made a mistake, they should come back and rewire the exhaust fan correctly!

Backdraft Flapper Might Be Stuck Closed

Typically, a bathroom exhaust fan system will include three essential parts: the exhaust fan, the vent pipe or duct, and a backdraft flapper where the air exits the home. As the name suggests, that flapper ensures that a backdraft doesn’t happen.

That flapper works in a very straightforward way. As long as there’s air coming out of the vent, the flapper stays open. However, when you shut the exhaust fan off, the lack of air will cause the flapper to shut by itself and prevent dust, dirt, and debris from entering the vent.

Unfortunately, the backdraft flapper may get stuck in the closed position. As the exhaust fan blows air towards the flapper, that air fails to escape and instead returns into the bathroom.

To resolve this issue, it’s essential to take a very close look at the backdraft flapper. Typically, a quick spray of oil could be enough to lubricate the flapper, so it opens and shuts quickly. However, a heavily rusted backdraft flapper may need to be replaced entirely. 

Vent Pipe Or Duct Is Undersized

When installing a bathroom exhaust fan, the air duct must be big enough to match the power of the fan’s motor. Simply put, the vent needs to accommodate all the air that the exhaust fan will continuously push through it.

If, for example, the duct is too small, then the air will not be able to flow through efficiently. That could result in some air returning to the bathroom exhaust fan, creating the impression that there’s air being blown back down into the bathroom.

This is a common mistake that happens when homeowners try to install a bathroom exhaust fan system. First-timers may overlook or underestimate the importance of correct sizing when it comes to the air ducts.

To avoid this, it’s always a good idea to consult the exhaust fan manufacturer or even a qualified technician. Both of them will advise you on the correct sizing for the fan’s air duct.

Vent Pipe Or Duct Might Be Blocked

Despite being the correct size, it could also be that the vent duct is blocked. This is a common reason in households where the exhaust fan has been in use for many years.

Unfortunately, many owners tend to forget that dust and debris can build up in an air duct over many years. When that build-up becomes large enough, what happens is that more of the air that flows in that vent will get turned around. 

As a result, that air makes its way back into the bathroom rather than outside the house.

Thankfully, the solution to this problem is straightforward, and you can do it all on your own. Just like with the air vent or duct for a household dryer, the one for a bathroom exhaust fan must also be cleaned once in a while.

By cleaning out any dirt or debris inside the duct, air can flow very quickly from the fan all the way through and out of your house.

Vent Pipe Or Duct Kinked Or Flattened

Last but not least, another possibility is that the exhaust fan’s air duct might have become kinked or flattened. Typically, these air ducts are made of soft materials. If something were to fall on them, it would quickly become kinked or flattened, and air would fail to flow through.

Another reason for this is that air ducts typically go through the ceiling or roof of a home, where other pipes and equipment might be located. While someone is working on something else up there, like any part of your home’s HVAC system, they might accidentally flatten the air duct for your bathroom exhaust fan.

Rather than flow out of the house, some of that bathroom air will turn around and flow right back into the bathroom it came from.

This, too, requires a very straightforward fix. All that’s needed is for you to inspect every part of the air duct and straighten out any kinked or flattened parts. That will allow proper airflow to resume, and air won’t blow back into your bathroom.

Final Thoughts

Put, if you feel that your bathroom exhaust fan is blowing air down, it could be a problem with the fan blades or its wiring. More likely, though, is that there’s a problem preventing the air from flowing through the ducts and out of your home. When that happens, the air has nowhere else to go but to return to your bathroom.

Thankfully, most of these causes are pretty easy to fix by yourself without calling a technician to do it for you.