How to Vent A Bathroom with No Outside Access

  • By: Peter Allen
  • Date: 06/24/2021
  • Time to read: 4 min.

You will notice that builders and plumbers are extremely concerned about the proper vent in a bathroom while they build or remodel the bathroom space. It is essential since the space has baths, toilets, steamy showers, and even running sinks. And all these count for both dampness and odor inside the bathroom that needs ventilation to go outside.

However, the problem comes when a bathroom has no outside access for the venting system. So, we have dedicated this guideline on how to vent a bathroom with no outdoor access. Although venting a bathroom without proper outdoor access is challenging, it is not Mission Impossible.

How to Vent A Bathroom with No Outside Access

When you take a hot shower inside the bath or run the sink for a few minutes, often moisture will accumulate inside the bathing space. You will have to opt for the right venting system to allow such moisture and stinky odor to go outside.

If you don’t have access to outdoor space directly for the ventilation system, you have to find another way for the ventilation. You will need-

  1.  An HVAC contractor
  2. A bath fan

The HVAC contractor will install the right bath fan and create the proper ventilation process from the bathroom to the nearest outdoor point. It enables the fan to pass the moisture and smell from the bathroom into an outdoor space. Thus, the bathing space remains dry and hygienic.

Choosing the Right Bath Fan

You will have to pick the right fan for installation inside the bathroom to ensure a proper venting system. You need to consider the following factors for it.

Fan size:

The bath fan size refers to how much air volume it can move at one given time. The size of the fans is measure in Cubic Feet per Minute (CFM). It means how many cubic feet of air the fan can remove in one minute.

Ideally, for each square foot of bathroom space, the fan needs 1 CFM of capacity. Hence, a standard US bathroom would need a venting fan with 40CFM capacity for proper efficiency. Apart from the bathroom size, you will also have to determine the frequency of bathroom use accurately. For instance, if multiple people use the same bathroom, you will need a slightly higher-capacity CFM for the fan. Also, consider the sink running time for the most accurate fan size.

Bathroom Specifications:

Next, you should consider the bathroom specifications to choose the right fan for it. For instance, half baths don’t have shower space. So, it has less wetness and moisture. Thus, you can pick the recirculating fan for the half baths.

However, it only passes the air from outside to the bathroom using a filter. Thus, it only removes the odor.

If the bathroom is located far away from the exterior wall, your best bet would be the underneath vent. HVAC contractors will install such vents between the exhaust point and the floor joints correctly. It will then run right through the exterior wall to the outside space for the best venting results.

If you live in a small studio apartment inside a big building, your bathroom will less likely have outdoor access for ventilation. Thus, you need to consider commercial ductwork for it. It ensures that the bathroom remains dry and hygienic with one long duct system. You can additionally build a soffit to hide the duct vent outside for aesthetical purposes.

Should You Hire A Professional HVAC Contractor for Venting A Bathroom Without Outdoor Access?

Ideally speaking, you can install the bath fan with a simple DIY project. It doesn’t need much effort. However, you have to ensure that the bathroom fan is positioned properly and the air passes from the outside to the bathroom accurately.

At times, you might not feel comfortable with the installation process. Also, it runs the risk of damaging the bathroom walls. Thus, we recommend you call for professional help to mount the bathroom fan for ventilation. Also, an HVAC contractor is a must when you have to install the vent beneath the bathroom to the exterior space.

How Costly Is the Bathroom Vent Installation Process?

The actual cost will depend on the fan size and type of duct system you will use inside the bathroom for the ventilation process. However, most experts say that bathroom fan and vent installation is priced moderately.

On average, a standard US bathroom vent installation will cost anywhere from $210 to $540. It doesn’t include the cost of hiring professionals. If you need professional help, the cost might go up to $2000 for the entire setup.


Many homes these days come without any outdoor access to the bathroom. Thus, you need to know how to vent a bathroom with no outside access. You will have to select the right bath fan for it firstly. Then, you can mount the fan with a DIY project or call for professional help.

Also, be ready to spend a hefty amount on the vent installation process.

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