3 Bathroom Exhaust Fan Venting Options (+ Codes)

Bathroom exhaust fans need to be vented. There is just no way around that. There are several bathroom exhaust fan options, including how to vent a bathroom with no outside access.

Does a bathroom exhaust fan need to be vented outside?

Not necessarily.

In short, there are two major categories of bathroom exhaust fan venting options:

  1. Indoor venting. Example: Do bathroom exhaust fans need to be vented outside? Not necessarily. The bathroom vent into the attic is an example of indoor bathroom fan venting (code requirements, as explained further on, advise against it, however). We’ll look at how you can vent a bathroom with no outside access.
  2. Outdoor venting. Venting a bathroom fan through the wall (sidewall) or through the roof are examples of a standard outdoor bathroom fan venting.
bathroon exhaust vent venting options
Example of installed bathroom exhaust fan (achieving above 50 CFM intermittent airflow).

We are going to cover all the options (both indoor and outdoor venting) you have to vent a bathroom fan, with a short step-by-step vent installation process.

Prior to this, however, we need to look into bathroom exhaust fan code requirements (specifically Section R303.3, Section R303.4, Section M1507.2, Section M1507.4 of the Internal Residential Code (IRS)).

Now, these codes can be tedious to dig through. Nonetheless, these very bathroom ventilation requirements are the key guidelines we can use (actually, we are required to use them) to properly ventilate a bathroom.

Let’s cover the simplified version of these ventilation codes. Understanding these will allow us to adequately choose the best exhaust fan venting option for your bathroom later on:

Bathroom Exhaust Fan Code Requirements

Code requirements are covered in International Residential Code (IRS). Specifically, residential bathroom exhaust fan code requirements are covered in Section R303 Light, Ventilation, and Heating.

The most important parts for bathroom venting are Chapters R303.3, R303.4, R303.5.

In the simplified version, these codes state that: “Bathrooms, water closet compartments, and other similar rooms shall be provided with an aggregate glazing area in windows of not less than 3 square feet (0.3 m2), one-half of which shall be openable.”

That simply means you need a sizable window through which the bathroom can be vented. Simple, right? Well, not that simple if you don’t have a window, or your window is not big enough (at least 3 sq ft).

Here’s where bathroom exhaust fans come in. The code also considers bathroom with no windows or small windows and states that if you get ‘air infiltration rate of a dwelling unit is 5 air changes per hour or less’, you have to use mechanical ventilation. That mechanical ventilation are basically bathroom exhaust fans.

One big part of bathroom ventilation fan requirements cover the size of the fan you need. Something in terms of ‘you need a 20 CFM continuous vent or 50 CFM intermittent vent’. You can check the whole code here. The easiest option is for sizing a bathroom exhaust fan is to use our CFM calculator here.

The second big part are the venting options. To paraphrase as simply as possible, here is what the code says:

  • Bathroom fan has to be exhausting the air to the building exterior (outdoors).
  • Bathroom fan cannot be exhausting the air into attics, crawl spaces, or otherwhere inside the building.

This basically answers the following key question:

“Do bathroom exhaust fans need to be vented outside?”

Yes. Residential bathroom exhaust fan code requirements for any bathroom fan to be vented outside. Example: Can you vent a bathroom to the attic? No, according to the code requirements, you cannot vent a bathroom vent to the attic.

Of course, it’s still possible to install a bathroom vent to the attic. You just need to be aware that this is not permitted by the current bathroom fan code requirements.

It’s just important to keep these code restrictions in mind when you’re installing a vent.

Now, with all this in mind, let’s look at how to vent a bathroom fan and what bathroom venting options are available to you:

How To Ventilate A Bathroom Without Windows?

The name of the game here is how to vent a bathroom exhaust fan. This, of course, implied that you don’t have a bathroom window.

With a big enough bathroom window – at least 3 sq ft and achieving a minimum of 5 air changes per hour – you just ventilate a bathroom through that window.

Here we will list options of how to vent a bathroom with no outside access. This includes ventilating a bathroom fan through the wall, through the roof, to the attic, through soffit, to the ductwork, and through the gable:

1. How To Vent A Bathroom Fan Through The Wall? (+Installation)

The most popular way to install a bathroom fan is through the wall. It’s pretty much the easiest and most widely available way to ventilate a bathroom with no window.

For through-the-wall ventilation, you basically just need to pick the right side bathroom exhaust fan and install it through the wall. That will require you to make a hole in the wall. On the inner side, you have the bathroom, and on the outer side, you have the outdoors; this is smooth ventilation.

Here is a short step-by-step DIY way how to install a bathroom vent through the wall:

  1. Choose a position on the wall where you want to install a bathroom exhaust vent. Where to place a bathroom exhaust fan? You want to reduce moisture, and humid air sinks to the floor. You should place the fan nearer the bottom of the bathroom (maybe 1 foot above the floor in order to secure the vent in the event of a bathroom flood).
  2. Measure the fan and label the wall. Use a measuring tape to measure the fan dimensions, and label these dimensions on the wall. Example: If you have a 12×12 inch fan, mark that 12×12 on the wall. You’re basically labeling where the hole through the wall should be.
  3. Make a hole through the wall. This is the key part of how to install a bathroom exhaust vent through the wall. In most cases, you can use a power saw to cut out that part of the wall. Use a hammer to smash the remaining part. With tougher walls (stone), you will need more powerful tools.
  4. Clean the whole of all the rabble. It’s essential that you have a clear opening before inserting the bathroom exhaust fan.
  5. Insert the through-the-wall bathroom exhaust fan. Make sure to attach the fan to the joists (you use 1 1/2-inch screws on each bracket end).
  6. Attach the outdoor wall cap or shutter. Tighten it with screws.
  7. Fix the electrical connectors. This will take care of the wiring, and connection to the electric grid.

This is the 101 of how to install a through-the-wall bathroom exhaust fan. It does need some technical skills and time but it’s the most elegant way to ventilate a bathroom without windows.

2. How To Vent A Bathroom Fan Through The Roof?

Another way to vent a bathroom exhaust fan is via the roof. You can think of this roof vents for bathroom fans as through-the-wall vents; just replace the wall with the roof.

The key adjustment here is to make sure to insulate the outer part well. The primary purpose of the roof is to keep your house dry. Any hole in the roof, even that from the bathroom exhaust fan, is not acceptable.

That’s why you usually use asphalt roof cement to cover the whole exhaust fan creates.

For the step-by-step way of how to install a bathroom exhaust fan through the roof, you can check the previous chapter for the wall installation.

The process is pretty much the same – instead of cutting a hole in the wall, you’re cutting a hole in the roof. You might need some additional flexible 4-inch or 6-inch ducts. Do make sure at 6th step: attaching the outer shutter cap. That cap must withstand heavy rain and even snow.

3. How To Vent A Bathroom Exhaust Fan Into Attic?

It’s quite incredible how many homeowners are left with only one possible ventilation option: to vent a bathroom fan into the attic.

Now, a lot has been written about bathroom fan to attic ventilation option. You might even know someone who has a bathroom exhaust fan channeled to the attic, or have seen such an installation.

Needless to say, it’s practically possible to install a vent from the bathroom to the attic. The only thing you pretty much need to do is to drill a hole between the bathroom and the attic; you can look at the through-the-wall installation process.

However, you should heed the IRS guidance here. It’s not all that smart to channel a high relative humidity air from the bathroom to the attic. That may increase the risk of moisture growth in the attic. That’s why it’s not advisable to vent a bathroom fan to the attic.

On top of that, the IRS requirement codes specifically advise against (we could even use the word ‘forbid’) venting the air from the bathroom into the attic via a bathroom fan.

3. How To Vent A Bathroom Fan Through Soffit?

Venting a bathroom fan through soffit is usually easier than through the wall or through the roof. That’s because soffit is not as thick as the wall and it’s easier to cut through.

To install a bathroom fan through soffit, just follow the through-the-wall installation process described above. You can fit of soffit just as a less tricky wall to work with.

Bathroom fan through soffit installation is also not advised against in the code requirements. It is bathroom ventilation outdoors, you can achieve either 20 CFM continuous airflow or 50 CFM intermittent airflow, and it’s basically one easy way how to vent a bathroom effectively.

Hopefully, you will find all this useful in deciding how you want to vent your bathroom with no windows.

Leave a Comment