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How to Vent a Bathroom With No Outside Access

Bathrooms without outside access are actually fairly common. You are not alone in having to work out how to ventilate and dehumidify your bathroom without the space to run ductwork through the ceiling above or directly through an exterior wall.

There is one way to go about this if you are looking for a code-compliant and effective ventilation method. Any other methods are temporary and likely won’t be acceptable for building code regulations.

Exhaust fan ductwork can be run along the bathroom-side of the ceiling and vented outdoors through an adjoining room. A high-capacity dehumidifier and leaving the door open to vent the bathroom into adjoining rooms can provide ventilation but is temporary and may not suffice to ensure code compliance.

Clarifying “No Outside Access”

For the purposes of this article, we will be assuming that by “no outside access” you are in a situation where all the typical forms of ventilation are unavailable to you.

  • There are no windows.
  • There is no ceiling access or space to accommodate the ductwork of a ceiling- or wall-mounted exhaust fan. This could mean that the space above the ceiling is full or the ceiling is a concrete slab.
  • There is no external wall through which a wall-insert fan can be installed.

If you are simply in a bathroom that has no windows but there is ceiling access or an external wall, then you can rather read through my article on venting a bathroom without windows for some effective methods.

First Prize: Alternative Venting for Exhaust Fan

If it is possible, you can still install an exhaust fan. This is always going to be the best option.

To make this work, you would need to run part of the ducting on the underside of the ceiling (the side that is visible in the bathroom) and take this through an adjoining wall into a room where there is more ceiling space or there is an external wall.

Ceiling insulation ventilation system air ducts fire extinguishing

This method will allow you to properly ventilate your bathroom with just a little extra ductwork.

This doesn’t exactly sound attractive, but there are ways to cover it, and it will ensure you comply with building code ventilation rules.

Hide the Ducts With Bulkhead or Drop Ceiling

A bulkhead or drop ceiling will conceal what would be exposed ductwork in the bathroom (and any in the adjoining room).

Your concern here may be the height of the ceiling. The drop ceiling will take up some of the air space in the bathroom. A bulkhead is more precisely targeted as it fits around the ducting, meaning that this would only affect the ceiling height in the area where the ductwork is.

There are several considerations for installing a drop ceiling in a bathroom:

  • Section R305.1 of the International Residential Code (IRC) states that there is a minimum height requirement for a bathroom at 6’8”. There are exceptions for sloped ceilings, but there must be enough space above the showerhead and toilet.
  • You must use materials that are moisture resistant. There are different materials that you can use depending on your needs and decor goals.
Modern interior with drop ceiling

Do Not Vent Into the Adjacent Room!

There are at least 10 reasons why you shouldn’t vent the bathroom into another room. We will look at the most immediate issues, but I recommend taking all these reasons into consideration.

  • Building code regulations do not permit bathroom air to be exhausted into any other area of the house, as per Section M1505.2 of the IRC. The IRC, Section M1501.1, requires the exhausted air to be discharged directly to the outdoors. So, if you vent the bathroom air into the adjoining room, your house is non-compliant.
  • The damp bathroom air can damage furniture and fabrics. The structure of the other rooms can also be damaged, and this can result in collapsing, rotting, and molding walls, floors, and ceilings.
  • Other rooms are not generally equipped with the moisture-resistant electrics that the bathroom has, and this can quickly become dangerous.
  • Bathroom fans are designed to help deal with unpleasant bathroom odors, which would be released through the house.
  • Without the intentional discharge of the bathroom air, it may end up re-entering the bathroom and defeating the purpose of ventilating the bathroom.

Dehumidifier + Open Bathroom Door

A bathroom fan’s function is to remove moisture and provide ventilation. Technically, you can achieve this without a fan by using a dehumidifier and leaving the bathroom door open.

However, at best this can only be used as a temporary solution.

A dehumidifier’s function is to remove moisture from the air around it, so this would take care of the dampness. Leaving the bathroom door open and allowing the exchange of air in and out of the bathroom is a way of ventilating the room.

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You will need to use a dehumidifier powerful enough to tackle the moisture of a bathroom, and you will likely need to take a few measures to ensure that you are getting the most airflow using the door opening.

Dehumidifier Must Be High-Capacity

Any dehumidifier you choose to use in a bathroom without an exhaust fan must have the capacity to dehumidify the air the way a bathroom fan would. That means you will need a high-capacity unit.

If your dehumidifier cannot cope with the amount of moisture in the air after showering and bathing, then it is not acting as the solution you need it to be, and you will likely have to run it for longer periods. This uses more energy, creates more noise, and will cost you in higher utility bills.  

Fortunately, I can provide you with a list of 7 of the best dehumidifiers for a bathroom without an exhaust fan, with details and the pros and cons for each unit. At the top of the list (should it fit your needs) is the Inofia 30 Pint 1,500 Sq. ft. Home Dehumidifier (amazon link).

Different dehumidifiers have different methods of draining, some of which may be more or less convenient for your situation. So, ensure that the dehumidifier you are choosing will be able to operate (and fit!) in the bathroom and be able to remove enough moisture.

Enhancing Effects of Open Door

Dehumidifying the bathroom is the easier side of it; ensuring there is sufficient ventilation is the hard part.

Open Windows in Adjoining Rooms

By opening the windows in the adjoining rooms, you are engaging a natural ventilation system. As a result, air can circulate through the rooms and should push out the air you need to get rid of from the bathroom.

This is not convenient during winter and storms as you would need to leave the windows in adjoining rooms open for long enough to refresh the bathroom air. Additionally, as this is non-mechanical ventilation, there are factors, such as heat and wind speed, that will impact the quality of the bathroom’s ventilation.

I would consult with a professional in your area to find out the minimum time that you will need to have adjoining windows open to maximize ventilation after a shower.  

Take Advantage of Whole House Ventilation

Houses have a general ventilation system. This can be utilized for helping to ventilate your bathroom.

Opening windows and doors at the higher points in your house and the lower points increases passive ventilation. AC units, range hoods, and soffit vents will all assist with circulating air around your home and exchanging stale air inside for fresh air from outside.

Modern interior HVAC Ventilation

By leaving the bathroom door open, you are including this room in the general ventilation, which may help to ventilate the bathroom.

Turn on Kitchen Range Hood

Range hoods, like bathroom fans, are good for exhausting warm and moist air, so you might try putting it on to help with proximity ventilation.

The trouble here is that the bathroom would need to be close enough to the kitchen for this to have any sort of benefit. Even in those cases, the range hood will never accomplish what a bathroom fan can.

The other issue is this: if your bathroom is close enough to share air with the kitchen, now you are going to intentionally be venting bathroom air and all its unpleasant odors in your cooking and food space.

Leave Door Open While You Shower as Well

By leaving the door open while the shower is running as well as afterward, you prevent the troubles of moisture and heat building up in the bathroom. You’re allowing the bathroom to be ventilated during the process instead of getting rid of it once it has amassed.

This, however, impacts the matter of privacy. It might not be a problem to leave the door open while you shower if you live alone or with a significant other, however, it won’t likely always be acceptable.

If you have guests visiting or staying over, needing to keep the door open becomes awkward. This is also not a great resale feature.

You might try adding a ventilation grille into the door to allow for air exchange with the door closed, but an open door will still be best while the shower is running as well as after.

Contact Professional for Approval

The building code has rules and regulations for ventilating a bathroom and to contravene them is to go against lawful requirements.

A dehumidifier is not an alternative to ventilation. The open door would provide ventilation; however, there is a strong possibility that this open door will not be considered code-compliant even if it works well enough.

A local professional, such as an HVAC specialist or a home inspector, will be familiar with the ventilation requirements for your area and will be able to help you assess what is needed to abide by the building code.

Even if there is a situation in which an open door would be sufficient ventilation, it would still be prudent to get a professional to confirm that everything is according to regulation.


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