When I inspect homes for buyers, I have seen so many different bathroom venting installations — it would make your head spin.
Some of these bathroom fan venting options are terrible, like burying a vent under the attic insulation, leaving the vent inside a wall cavity, or venting the fan to a bedroom, garage, or basement.
There really are just a handful of recommended bathroom fan venting options such as venting to the exterior wall, to the gable, and to the roof.
All of these bathroom venting options have their pros and cons but keep reading to get into the details.
Option #1. Exterior Wall
The most common bathroom venting option is when the exhaust fan is installed in the ceiling or wall, and the vent goes to a close by exterior wall.
The bathroom vent may have one or two additional bends or turns — but ultimately it still goes to an exterior wall.
A vent hood is installed on the exterior wall which will include a flapper and possibly a screen to keep out any pests as well as prevent air or water infiltration.
Option #2. Gable
If your bathroom is on the uppermost level of the home, installing the vent through the attic and to the gable is very common.
The gable is the triangular portion of the exterior wall which is in-between your roof pitches.
And since you have access to the attic, it can make the installation significantly easier.
Whenever installing a duct through the attic (or any unconditioned space), we always recommend installing an insulated duct to prevent condensation from forming inside the vent.
The duct will also need to be supported in the attic every few feet with straps. The duct shouldn't be loosely laid over insulation or the floor of the attic.
Any time the attic insulation gets compressed, it ruins the R-value or effectiveness of the insulation.
And again, homeowners will also need to install a bathroom vent cover which has a flapper to keep out pests and air infiltration.
Option #3. Roof
The third most common place to vent your bathroom fan is directly to the roof.
A special metal roof vent is installed that keeps out rain and animals.
The roof vent needs to be very durable to withstand the exterior weather — it needs to be much tougher than the cheaper plastic wall vent covers.
We recommend buying metal roof vent covers that are made out of galvanized stainless steel so it can withstand the outdoor weather and avoid rust.
The downside of venting to the roof is that there will be a possibility of future leaking. The usual rule is that the less holes in the roof, the better.
But, this shouldn't stop homeowners from venting to the roof since it is an extremely common installation. I definitely recommend having a licensed roofer install the bathroom fan roof vent.
Option #4. Vertical Wall Installation
The fourth option for homeowners is to install the bathroom fan on the vertical wall of the bathroom.
Even though ceiling installation is always the best and recommended, sometimes it may just be easier to install the bath fan on the wall.
There are two types of bathroom fans that can be installed vertically: low profile and through-the-wall exhaust fans.
Through-the-wall bathroom fans vent immediately to the outside with a duct run of just a few inches.
Through-the-wall exhaust fans usually come as kits and come with the exterior cover, a short duct section, and other parts needed for installation. These through-the-wall exhaust fans aren't just used for bathrooms, but are also frequently installed in kitchens, garages, mud rooms, and other locations.
Low profile exhaust fans are really just regular bath fans except for the fact that the housing is thinner than normal. This means that low profile exhaust fans can be installed in-between the wall studs and then vented to the outside.
Unlike through-the-wall exhaust fans, low profile fans have their ducts coming out the side so the duct length will have to be a little longer, and there needs to be at least one turn.
Option #5. Soffit Installation (Not Recommended)
Probably one of the least common bathroom exhaust fan venting installation is to the soffit. The soffit is the underside of your roof overhang, and there is usually a type of passive venting installed there called soffit venting.
Homeowners should check with your local building code on this one because not all municipalities will allow this venting option.
At Home Inspector Secrets, we do not recommend a soffit installation because it can cause mold problems in the attic if there is existing soffit ventilation.
Soffit vents are intake vents on the roof overhang that pull in cooler exterior air through the soffit and up and out the ridge vent (very top of roof).
If you install a bathroom fan vent to this area, the soffit venting may actually pull in the exhausted moist air from the bath fan — completely ruining the exterior venting.
At minimum, homeowners should close off any nearby soffit vents so that it doesn't suck in the bath fan exhaust back into the attic.
There are also custom bathroom vent covers designed to be installed on the soffit. Some of these vent covers are spring loaded so that when the air flow stops, the spring pulls back the cover to prevent air and animal intrusion.
Option #6: Attic Termination (Not Recommended)
Although this is my least liked option and not recommended, many older homes have bathroom vents that terminate in the attic.
Almost all building codes state that contractors are not allowed to exhaust bath fans into attic spaces.
However, I still come across it quite often. Older homes will also be grandfathered in to newer building codes.
When I find bath fans venting into the attic, they are quite often just laid loosely on the attic insulation, or even worse — buried under the insulation.
But more commonly, the vent actually goes near the outside but stops a few inches below the ridge vent, a few inches behind the gable vent, are laid atop the soffit vents.
The big problem with bath fans venting in the attic is that all of the shower moisture that gets blown into the attic may lead to wood damage, mold growth, and poor indoor air quality.
The moisture in the attic can also attract pests like termites.
Insulating Your Bathroom Fan Duct
One commonly overlooked consideration is insulating the duct hose as it goes through the attic area (or any unconditioned part of the house).
If the attic air is very hot, and the bathroom air getting exhausted is cold, then these temperature differences may cause water to bead on the outside or inside of the vent and ultimately cause moisture damage or mold.
It can also work in the opposite situation, when the attic air is cold, and the exhausted air is warm.
The easiest solution is to buy a bath fan duct that comes with an insulated sleeve. The insulation will help prevent any condensation or water drips on the bath fan duct.
Avoiding Bird Nests
One common downside of venting a bath fan to the exterior wall or gable is that it is vulnerable to animal intrusion.
Birds typically cause the most problems with vents because they love to nest inside bathroom (and dryer) vents. The nest can completely obstruct air flow which will make the bathroom exhaust fan more or less ineffective.
Homeowners need to make sure that the exterior vent cover has a pest screen and flapper to keep birds out.
I have done by best to breakdown the most common bathroom fan venting options for homeowners today.
Here are some of the highlights...
- Venting to the exterior wall and gable are the most common options
- Venting to the roof requires an exterior rated vent hood made out of metal
- Venting to the soffit is not recommended but homeowners should at least close off nearby soffit vents
- Venting into the attic is a code violation and may cause mold growth and wood damage
- We recommend installing an insulated duct if the vent goes through an attic, garage, or other unconditioned area to stop moisture
I hope you enjoyed this guide by Home Inspector Secrets.