The placement of the bathroom fan can make a big difference in how effectively it removes moisture and how the airflow affects people using the bathroom.
A bathroom fan should ideally be placed in the ceiling close to the shower, but not directly over the shower. While it is allowed to install a shower-rated bath fan directly above the shower, for maximum comfort it is best to install it slightly away from it.
There are a number of things that must be taken into account when deciding where to place a bathroom fan. Some more important than others. While the placement of the fan is important, the most important thing is that the bathroom fan is used regularly, and for long enough periods.
Placing the Bath Fan Close to the Shower Will Make It More Effective
While the bathroom fan will exhaust moist air out of the bathroom, no matter where it is placed, it will be more effective if placed close to the shower as shown in the illustration above.
By placing the fan as shown in the picture, the steam will be easily exhausted out of the house and fresh air will be drawn in from the gap under the door. The upside to this placement compared to placing it above the shower is that the shower corner will stay considerably warmer.
This placement makes it ideal to use a light/fan combo to keep the bathroom as minimalist as possible.
Don’t worry if you are not able to place the fan exactly as in the picture. As long as it is in the same general location you will be fine.
Placing the fan close to the shower will provide efficient ventilation while at the same time not compromising on comfort. As we will discuss next, placing the bath fan in or directly above the shower might not be the best idea.
Placing the Bathroom Fan Directly Above the Shower Makes the Shower Chillier
While many people recommend placing the bath fan directly in the shower. It’s not the best solution. Theoretically, it should make the fan more effective since it is closer to where the steam is generated.
However, in real life, there is no measurable difference in the speed at which the moisture is exhausted when comparing placing the fan above the shower, or close to the shower.
Since a bathroom fan exhausts air out of the bathroom, the same amount of air must come back in. This air is often much colder than the air in the bathroom and makes the person showering feel cold. Especially during winter time when the temperature of the rest of the house is low.
If the bath fan is placed directly above the shower, the colder air that replaces the exhausted air will move right past you and create a cold draft. The air that will move past you will be room temperature, but it will feel cold since the air in the shower is much warmer. Unless of course, you enjoy taking cold showers 🙂
When the bathroom fan is drafting cold air out of the fan itself, then the problem is with a defective backdraft damper.
So if there is no upside to placing the bath fan in the shower, and a high chance of a cold draft, it should not be installed in the shower. It is much better to place it a few feet from the shower, between the door and the shower.
The intensity of the cold draft depends on following factors
- Room temperature
- Bathroom fan capacity
- Where the make-up air is coming from
If you are not worried about cold drafts and you would like to install the bath fan directly in the shower, there are a couple of things that should be kept in mind.
Where Should the Bath Fan Be Placed in an Enclosed Shower
There is no risk for cold drafts in an enclosed shower since the air can’t flow directly on you. It must come under the shower stall door or through small cracks. This will slow the air movement and won’t cause a noticeable draft.
So is it a good idea to place the fan inside the shower stall/cubicle?
The same reason why a shower stall prevents a bath fan from causing a cold draft is preventing it from efficiently moving air.
Unless your shower enclosure has a large gap under the door( unlikely) then there will not be sufficient make-up air available. This means that fresh air can not replace the moist air that is being exhausted. This will make the fan much less effective and will negate any benefits one would get from placing the bath fan inside the enclosure.
If however, your shower enclosure has enough of a gap under the door(or any other opening) then it will be OK to place the fan inside it. The only benefit to doing this is that you don’t have to leave the stall door open after taking a shower. (if the fan is outside of the enclosure you should always leave the door completely open)
Keep in mind that some municipalities require a second bath fan if installing one inside the shower enclosure.
As with a normal shower, the optimal position is close to, but not directly in the shower. Placing the bath fan 1 foot from the shower enclosure door is best. Remember to leave the shower door open after showering, this will dry it out much faster.
In order for the air to move efficiently there should not be any towel racks, drawers or other furniture/appliances between the shower/bath and the bathroom fan.
Unfortunately, if the fan is placed somewhere not visible, e.g behind a large cabinet the airflow will not be as effective. Fortunately, there is a solution that offers no visible dust-filled bath fan grille and efficient ventilation.
If you wish to hide the fan you could buy a fan/light combo(amazon link). The one I linked to looks like a regular light. There is no visible vent grille that will be covered in lint.
Ceiling Mounted Fan is More Efficient
There are 3 different types of bathroom fans, but ceiling mounted fans are the most efficient because the steam from the shower moves up and will naturally move into the fan.
While it’s perfectly OK to install a bath fan on a wall, it will be less efficient. The warm moist air will be collected near the ceiling. As the wall-mounted fan exhausts air out of the bathroom, only some of it will be the moist air from the ceiling. Most of the air will be drawn from directly in front of the fan. Since likely there is a gap between the fan and the ceiling it will suck in some dry air as well.
It is best to exhaust the steam as fast as possible to prevent it from condensing on cold surfaces. This will decrease the time it takes for the bathroom to dry after taking a shower.
This is also why it is important that the bathroom fan CFM is correct for the size of the bathroom. You can use the CFM calculator to find out what is optimal airflow for your bathroom. A correctly sized bath fan will help keep the bathroom mold-free and depending on the bathroom temperature it could even keep the mirror from fogging up.
Consider Where the Fresh Air Is Coming From
Even if the bath fan is placed in the exact right spot if there is not sufficient make-up air available it will not work.
There must be a gap under the bathroom door or another means for air to enter the bathroom. If your bathroom door does not have a gap, don’t worry it is quite easy to trim it down.
Before you start cutting the door, test if it is even necessary. Install the fan, turn it up all the way.
Now open the bathroom door half an inch. If the air-flow tries to close the door, there isn’t sufficient makeup air available and you either have to cut the underside of the door or install a vent in the door.
I have seen people using weatherstripping on the bathroom door and eliminating the door gap to increase the soundproofness of the door. While it will make the door considerably more soundproof, it will also make the bathroom fan completely useless when the door is closed.
If the door is soundproofed, there must be an additional make-up air vent in the bathroom. Ideally, it should be coming from another room, not directly from the outside(this will prevent cold drafts)
Double Check the Attic for Any Obstructions
Before you decide on a location, take a look in the attic to see if there is sufficient space where you are planning on installing the fan.
If installing too close to the soffit there might not be enough room to move around and connect the duct to fasten the fan to the joists.
While you are up there, make a plan on how to run the duct and where to terminate it.
it is possible to terminate it either through the roof or through the soffit. I always recommend people who do not have previous roofing experience to go through the soffit. This way there is no risk for future water damage from the leaking roof vent hood.
What Else Besides Placement Is Important
While the location of the fan is important there are other factors that should be taken into account when installing a bathroom fan.
Here is everything that must be considered (I will discuss them in more detail later)
The size of the duct is crucial for the fan to work efficiently. An undersized duct will make the fan much louder and reduce it’s capacity to move air.
General recommendation is to use at least the same size duct that is on the bath fan housing connector. If the duct run is longer than 20 ft consider going up one size.
Rigid metal or PVC duct is preferable, If the duct run is short a flex duct can be used.
Find the shortest and straightest path from the fan to the termination point. The fewer turns and the shorter the duct is the more efficient the entire system will be.
Also, don’t forget to place insulation above the fan housing. Find out if your fan can be covered without clearance, or it needs a box for clearance.
The bathroom fan capacity is calculated according to the volume of the bathroom. I have created an bathroom fan CFM calculator you can use to find out the correct airflow.
It is important that the fan has sufficient capacity in order for it to dry the bathroom in a timely manner.
Must vent to the outdoors
The bathroom fan must ALWAYS vent outside of the building envelope. I can not stress enough how important this is.
In fact, having no bathroom fan could be better than venting it to the attic. If there is no bathroom fan the moisture damage from not having a bathroom fan will be visible in the form of growing mold in the bathroom. However, if the moist air is exhausted Into the attic or any other hidden space, the mold and mildew can grow for years without anyone noticing. This can end up costing tens of thousands to clean up.