Do you want to learn how to stop bathroom fan condensation?
Moisture inside a bath fan can have multiple causes, but there are a few very common ways to stop it.
In this guide, I will go over...
- How to stop bath fan condensation by improving airflow
- Why uninsulated bath vent hoses are a common cause of condensation
- And how buying a stronger fan (in CFM) may stop moisture buildup
Let's get started with this guide!
How To Stop Bathroom Fan Condensation?
Nothing can be more annoying than a bathroom fan that forms condensation everytime you use it. There can be multiple causes as to why this is happening.
In my view as a licensed home inspector, the first thing I would do to stop bathroom fan condensation is to check for proper airflow. If there is a vent clog or if there isn't strong airflow to the outside, then condensation can easily form in the bathroom fan resulting in dripping water. And after checking for airflow, and the attic is right above the bathroom, it is likely a insulation problem — either the attic is poorly insulated or the bathroom vent hose needs insulation.
Let's go over all of the ways to stop bathroom fan condensation in your bathroom...
#1. Remove Vent Clog & Improve Airflow
One reason you may be getting condensation in your fan is that the bathroom vent hose is clogged.
Many homeowners don't realize that birds love nesting in bathroom and dryer vent hoses. As a home inspector (and an air duct cleaning company owner), I have probably seen over a hundred birds nests in air vents. When a bird makes a nest inside a bathroom vent hose, it can partially or completely block the air flow.
In addition to a birds nest, the vent hose may be broken inside the wall, or there may be some other type of obstruction.
Just because your bathroom fan is making noise when you turn it on, don't assume that it is actually drawing air out of the house. An easy way to check if bathroom fan is actually working is to turn it on and place a small piece of toilet paper up to the bathroom fan. There should be more than enough suction to keep that small piece of toilet paper to the fan.
Another test that I like to do is turn on the bathroom fan, and to locate the vent cover on the outside. If it is near ground level, you can put your hand up to the vent and feel the strength of the air flow. If the air flow is weak, then you may have some type of obstruction, or the vent hose may have too many turns, or the vent hose may just be too long.
This is also a good time to make sure that the damper or flap is actually working.
When the bathroom fan is on, the flapper should open allowing the air to exhaust to the outside. A broken damper may significantly impede air flow.
#2. Insulate Your Vent Hose
If your bathroom fan goes through the attic, and it isn't insulated, then this may be the culprit.
Any time something cold meets something hot (or vice versa), condensation can form. So if you are exhaust cool interior air through a very hot attic, condensation can form inside and outside the vent hose, as well as inside the bathroom fan, and dripping water is the result. And it is also true in the opposite situation, exhausting warm interior air through a very cold attic.
It is more rare, but if your vent hose goes vertically up an uninsulated exterior wall, this can also be the problem.
There are also fiberglass insulated flex ducts that are pre-sleeved with insulation.
You can check out my full guide on venting bathroom fans into attics right here.
#3. Replace Your Bath Vent Hose
Another way to fix condensation inside a bathroom fan is to switch to a rigid metal vent hose.
Most bathroom fans use a foil type corrugated vent hose, which means it has many tiny ridges. These ridges in the hose can impede air flow, and the flexibility of this type of hose can create bends where moisture can accumulate.
It will be a hassle to change the vent if it goes through an attic space, but it may be worth it.
In addition, you want to make sure that the vent hose is sloped towards the outside, and not back towards the bathroom. When it is slightly sloped to the exterior vent cover, then any condensation will drain to the outside, rather than back onto the bathroom fan. And if there are any bends in the hose, you want to keep them to as few as possible, and avoid any sharp turns.
#4. Increase Attic Insulation
If your bathroom fan is getting condensation is on an upper level with the attic just above it, and if that attic is poorly insulated — this also may be the cause.
Even if the bathroom fan vents to an exterior wall, and not to the roof, a poorly insulated attic can create a large temperature difference. If the attic is extremely cold, and you are exhausting humid and warm air from your bathroom, condensation can form in your vent hose as well as in your bathroom fan, and water drips down.
Quite often, when I am inspecting attics, I can visually see bathroom fans that are not covered in insulation. It looks like its just a big metal box, it's easy to see.
Read Also: What Are Your Bathroom Fan Venting Options?
#5. Buy A Stronger Bath Fan
Another possible way to fix a bathroom fan with condensation is to replace the fan with a higher powered unit.
Bathroom fan speed is rated in CFMs, which stands for cubic feet per minute — this is how much volume of air the fan exhausts in one minute. Most bath fans are in the 50-cfm (low) and all the way up to 150-cfm (very high). I would say the average bathroom fan CFM is in the 70-cfm to 120-cfm range.
The minimum amount recommended for bathroom fans is at least 50 CFM.
If you have an average or large sized bathroom, and your bathroom fan is only 50-cfm, then this may be the problem. You can read my full guide on choosing the right CFM for your bathroom.
#6. Clean A Dirty Bathroom Exhaust Fan
Similar to problems with a clogged or broken bathroom vent hose, having a very dirty bathroom fan can seriously impede air flow, and may be related to the condensation.
It can also become a fire hazard.
I have seen some very dirty bathroom fans in my career, and it is surprising that some people either don't notice it or don't bother ever cleaning it.
The bathroom fan cover usually has many tiny holes or slots that can easily become clogged with dust over time. If these vent holes are clogged, then the bathroom fan may only be sucking in 5% or less of the full amount of moist bathroom air.
Just cleaning this bathroom fan cover can significantly boost air flow, and may eliminate or decrease the amount of condensation buildup in the fan. My article on cleaning bathroom exhaust fans details the steps of cleaning.
#7. Use The Fan More
This is kind of a no brainer, but common sense isn't always common.
You want to make sure that everyone in your household uses the fan while they are bathing, and about 20-30min after the shower or bath. If you aren't using the bathroom fan enough during and after bathing, condensation may build up in the bathroom fan.
And even though most people understand that you should use the bathroom fan while taking a shower — not everyone realizes that you are supposed to use it for at least 20-min afterwards.
Some homeowners I suspect turn off the fan after the shower because they want to save energy. But there is a simple solution: buy a bathroom timer.
There are special wall switches with adjustable timers that you can set for 10min, 20min, or 30min. So when you turn on the bathroom fan, it will automatically shutoff at your pre-determined time.
And there you have it, my list of possible ways to stop condensation in your bathroom fan.
The absolute first thing I would do is check if there is proper air flow. The easy way is to put a piece of toilet paper to the bathroom fan and see if it sticks. Then I would turn on the fan, and locate the exterior vent cover, and check the air flow.
Is the air flow strong?
And is the damper or flap working?
If the air flow is strong, I would move on to some of the other possible ways to stop condensation and dripping water.
Read Also: How To Vent A Bathroom Fan Through A Wall?