Where Do Bathroom Fans Vent To?


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Bathroom fans must vent to the outside of the residence. They may not vent into the attic, crawl space, soffit, or ridge vent. The IRC has regulations regarding where and how the ducts must exit the residence to discharge the bathroom fumes. They can exit through a wall, the soffit, or the roof.

Steamy bathroom air and toilet odors can permeate through the house if the bathroom is not adequately vented. Builders and HVAC contractors install bathroom fans that channel the air through a duct and out a vent. The placement of the vent exit is essential. There is even legislation that governs how and where vents may empty air from residences. 

It is sometimes challenging to know all the regulations regarding the structure and design of our homes. There is legislation that may look daunting, but it is not difficult to understand once it is explained. 

Bathroom Fans Must Vent Outside

The International Residential Code (IRC) provides the regulations governing where a bathroom vent may release the air that is removed from the bathroom. Section M1501.1 of the IRC states that:

“The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section M1506.3. Air shall not be exhausted into an attic, soffit, ridge vent, or crawl space.”

You also cannot vent the bathroom fan into the plumbing vents, although this may seem like a convenient solution.

As it contravenes the building code to vent anywhere except outside, doing so can compromise your insurance, should you have a claim, and it can even affect the saleability of your house.

Related article: Is There a Bathroom Fan That Doesn’t Vent Outside?

Can You Vent a Bathroom Fan Through a Wall?

If one of your bathroom walls is also an external wall, it is logical and easy to vent your bathroom through the exterior wall. It is more difficult to vent a bathroom through a wall if the bathroom walls are all interior walls. In some cases, however, venting through a wall may be your only option, such as when the bathroom is in the basement

There are advantages to venting a bathroom through a wall rather than the roof, the most notable of which is that the vent in a wall is less likely to leak if it rains.

A disadvantage is that the vent opening may create too much moisture on the exterior surface of the wall (particularly below the vent), which can cause rust stains to develop and possibly even mold.

Edge of a rectangular ventilation grill in a roughly plastered concrete wall with rust stains. Industrial background

An easy way to prevent vents from dripping is to install a backdraft damper.

I highly recommend AC infinity dampers(Amazon). They are spring-loaded and rubber sealed which ensures that there will be no air leaks (which cause the dripping)

If you are unsure how to place the vent through a wall and need more instruction, then check out the complete guide to how bathroom fans should be vented.

Correct Location of the Outside Vent

Section M1504.3 of the IRC provides the following three stipulations regarding the location of the bathroom exhaust vent:

Vents must open in the correct areas on the external walls. The IRC states that vent openings must be 3 feet (914 mm) or more away from the property border. This regulation prevents your bathroom exhaust air from creating problems for your neighbors.  

In addition, the bathroom exhaust vent cannot open less than 3 feet away from openable windows and doors or gravity air intake openings (louvers, slats, etc., for natural movement of air into the building). It would be pointless to remove the air from the bathroom, only to filter back into the residence through one of these openings! 

The bathroom vent must open 10 feet (3048 mm) or more from a mechanical air intake opening. These openings suck in the air and thus would absorb the bathroom exhaust back into the building. There is an exception to the regulation if the bathroom vent opening is at least 3 feet above the mechanical air opening. Working on the premise that hot air rises, the mechanical air opening would not risk taking in fumes from the bathroom vent.

Then, section R303.5.2 of the IRC states that the bathroom vent cannot empty onto a walkway. As you can imagine, it would be unpleasant for pedestrians to get a face full of bathroom exhaust fumes. It could also be potentially hazardous to their health.

Can You Vent a Bathroom Fan Through the Soffit?

For those who don’t know, soffit is the material used to cover or finish the underside of the roof overhang. It is possible to vent the bathroom through the soffit. However, it is important to remember that the vent cannot empty into the soffit. So, it can go through the soffit but must not have an outlet into the soffit. 

Venting the bathroom through the soffit requires careful consideration in choosing the correct materials and sizing of the ducting. The climate in which you live will also determine the material you select for ducting. To help you purchase the proper ducting and for some further tips and advice, take a look at this article on venting through the soffit.

Can You Vent a Bathroom Fan Through the Roof?

Venting a bathroom fan through the roof is the most common method. Builders and HVAC contractors choose this option as it is the easiest method in terms of installation; they do not have to cut through brickwork as might be necessary if they vent through a wall. The ductwork is also not as complicated as venting through the soffit, for example. 

There are various roof vents available. These can be chosen according to the best option for the residence and the homeowner’s budget.

Installing the roof vents must be done correctly to prevent rain from leaking through into the attic. Roof vents have flanges that fit under the roof shingles to prevent roof leaks. but these must be carefully installed to avoid having to repeat the job at a later stage. 

The positive aspect of venting through a roof is that you use the natural laws of physics to remove the moisture and heat from the bathroom. Hot air always rises, and this assists in the functioning of the vent. If you need some more information on bathroom venting, visit this article on How bathroom fans should be vented.

Related article: Wall Vs Ceiling Bathroom Fan (Pros and Cons)

Problems With Venting Into a Crawl Space or Attic

A bathroom should never be vented into a crawl space or attic.

  • The damp air compromises the structural integrity of the home.
  • Moisture encourages the growth of mold and bacteria, which can cause serious health hazards and break down the structural materials.
  • Rodents and insects are attracted to warm, moist, dark areas such as crawl spaces or attics if the bathroom vents empty into them. 
  • Bathroom odors can spread throughout the house if the bathroom vents into these areas.
  • Bathroom vents that empty into the crawl space or attic can increase the entire temperature of the home.
  • It also makes these spaces unusable as they are damp and moldy.
  • This practice contravenes the IRC regulations and will affect the insurance of your home. 

Related article: Can a Bathroom Fan Be Vented Down

Sources

https://codes.iccsafe.org/content/IRC2021P1/chapter-15-exhaust-systems

https://up.codes/s/light-ventilation-and-heating

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Joonas

I like it when I'm able to fix everything that needs fixing around the house. In order to do that, I have to do a lot of research. This site will cover everything I learn and maybe help others do the same.

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