How to Vent a Bathroom with No Outside Access

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If you don’t have a window or fan in your bathroom, it’s really important to properly ventilate the room so you don’t have to deal with any mold or odors. While most building codes require outside ventilation, you may need to update older homes. Luckily, there are lots of different solutions you can try to get some fresh air inside. Keep reading for everything you need to know about the signs of poor ventilation, the alternatives to an exhaust fan, and the venting options you have.

Things You Should Know

  • For an easy solution that doesn't require an exhaust fan, leave the bathroom door open and run a dehumidifier . Immediately dry any wet spots that occur.
  • For a more permanent solution, add a ceiling, wall, or floor duct vent fan. These don't usually cost more than $2,000 USD to install.
  • Over the long term, bathrooms definitely need some sort of vent to the outside in order to prevent mold and mildew.
Section 1 of 4:

Signs Your Bathroom Needs Better Ventilation

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  1. If you have no exhaust fan in your bathroom, fresh air won’t circulate in. The air in your bathroom may feel heavy or muggy, and you may also notice a musty smell if you leave the door closed.
  2. The moisture stays in the air whenever you bathe or shower if you don’t have a lot of ventilation, which can make your mirrors fog up. You may also notice condensation gathering on the walls or the other fixtures in your bathroom.
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  3. Since the smelly air won’t circulate out of the bathroom, you’ll notice odors from your toilet or strong cleaning products remaining much longer. Over time, the odors might build up and be overwhelming.
  4. Water builds up on your ceiling when you don’t have proper ventilation, so it will start leaving discoloration or water damage. It could also cause wood rot or peeling and bubbled paint. [1]
  5. Mold thrives in damp environments, so it can grow really easily in an unvented bathroom. Look for any stains or discoloration that have a fuzzy texture where the moisture builds up in your bathroom. With proper ventilation, you’ll be able to prevent mold from growing. [2]
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Section 2 of 4:

Easy Fixes without Using an Exhaust Fan

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  1. Crack your bathroom door while you’re showering if you can so the moisture can escape from your bathroom. When you’re finished in the bathroom, leave the door wide open for at least 15–20 minutes to help dry it out and let fresh air circulate in. [3]
    • If you have a glass shower door, leave it open so it can air out.
    • If you have a shower curtain, pull it closed after you finish since mold and mildew can form if you leave it pushed to one side.
  2. Standing water in your bathroom takes longer to completely dry out, and leaving large spills or puddles could lead to mold or mildew. Use a towel or absorbent bath mat to pick up any water on the floor as soon as you notice it. [4]
    • Hang up any towels you use in a different room since they won’t dry out as quickly in your bathroom.
  3. Set up a portable fan . When you’re finished in the bathroom, plug in a fan and point it out of your bathroom. The extra circulation from the fan will help any moisture dry up and get rid of any odors. Run the fan for at least 10–15 minutes before turning it off. [5]
    • Keep a window open in another room so the air from your bathroom has someplace to escape.
  4. Run a dehumidifier . In a pinch, you can use a dehumidifier to help draw the moisture out of the air. Set the dehumidifier in your bathroom and turn it on after you shower. Leave the door open and let the dehumidifier run until the air feels dry inside your bathroom. [6]
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Section 3 of 4:

Bathroom Ventilation Options

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  1. A ceiling vent either moves air straight up through the roof or horizontally to an exterior wall of your home. Calculate the power of the fan you’ll need based on the size of your bathroom and the fixtures you have to ensure that it vents properly. Typically, 90-100 CFM would be sufficient for a bathroom. If you’ve already got ductwork, you can install a bathroom fan on your own, but contact an HVAC contractor if you’re starting from scratch. [7]
    • Different fans have different noise levels, usually from 0.3 to 3 sones. The lower the better, but keep in mind that a quieter fan might require a bigger duct. While most fans have a 4-inch duct, the quietest models have a 6-inch duct.
    • Some ceiling vent fans have built-in lights so you can use them as another lighting fixture in your bathroom.
    • Ceiling vent fans can cost around $100–200 USD for the unit, but hiring someone to install new ductwork could cost upwards of $2,000 USD.
  2. Floor ducts run underneath your bathroom floor and horizontally to the exterior of your home. Fans installed in the floor work best if you can’t install a vent in the ceiling, like if your bathroom is underneath a staircase. [8]
    • Use a floor duct vent and a ceiling vent to circulate air through your bathroom faster.
    • The cost of a floor duct fan depends on if you already have ductwork in your floor and how it needs to reach for an exterior wall, but it usually costs around $1,500–2000 for the unit and ducts.
  3. A wall vent draws the inside air through the wall to the outside of your home, so they work if your bathroom is on an exterior wall. Wall vents are usually smaller than ceiling or floor vents, but they can be installed directly in an exterior wall without additional ducts. [9]
    • Air may blow inside through a wall vent, so install an exterior vent cover over the outside of the vent to help prevent backdrafts.
    • Wall vents usually cost less than $1,000 USD to completely install.
  4. If you already have vents in your bathroom but moisture still builds up, the air ducts may not be big enough or you may not have enough vents. You can install wider ducts in your wall to improve the airflow. You can also add multiple vents to your bathroom so moist air has more places to escape. [10]
    • Replacing and installing new ducts requires a lot of work inside your walls. Get estimates from professional HVAC contractors when you want to replace or install new vents so you don’t damage the system.
    • The cost depends on the length of the ducts, the size of your new ducts, and the cost of labor.
  5. A recirculating fan filters air through an activated charcoal filter to eliminate odors, but they don’t effectively vent out moisture. Since recirculating fans are ductless, they don’t take as long to install and are great for adding a little circulation to half bathrooms that don’t have a tub or shower. [11]
    • Check the building codes in your area since using recirculating fans might not be allowed.
    • Recirculating fans usually cost between $50–200 USD.
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Section 4 of 4:

Do bathrooms need to vent outside?

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  1. If you only vent your bathroom into an attic or another area of your home, the moisture and humidity could build up. The increased moisture makes it easier for mold to develop inside. [12]
    • Most building codes require any exhaust vents to lead directly outside.

Expert Q&A

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  • Question
    How do I lower the humidity in my windowless bathroom?
    Victor Belavus
    Air Conditioning Specialist
    Victor Belavus is an Air Conditioning Specialist and the Owner of 212 HVAC, an air condition repair and installation company based in Brooklyn, New York. In addition to HVAC and air conditioning units, Victor also specializes in furnace repair and air duct cleaning. He has over 10 years of experience working with HVAC systems.
    Victor Belavus
    Air Conditioning Specialist
    Expert Answer
    Open the door for better air circulation, use a dehumidifier to remove excess moisture from the air, wipe down any surfaces that may be wet or damp (like shower walls, the bathtub, and the sink), use a portable fan or ceiling fan to circulate air and reduce humidity, and use moisture-absorbing products like silica gel packs, baking soda, or activated charcoal.
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  • Question
    What is the best ventilation for a bathroom?
    Victor Belavus
    Air Conditioning Specialist
    Victor Belavus is an Air Conditioning Specialist and the Owner of 212 HVAC, an air condition repair and installation company based in Brooklyn, New York. In addition to HVAC and air conditioning units, Victor also specializes in furnace repair and air duct cleaning. He has over 10 years of experience working with HVAC systems.
    Victor Belavus
    Air Conditioning Specialist
    Expert Answer
    The best type of ventilation system for a bathroom is an exhaust fan. Exhaust fans are designed to remove moisture and odors from the bathroom and vent them outside. They are available in a range of sizes and styles, and can be installed in the ceiling or on the wall. It's important to choose the right size of exhaust fan for your bathroom to ensure that it effectively removes moisture and prevents the growth of mold and mildew.
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      References

      1. ↑ https://www.smchealth.org/sites/main/files/file-attachments/cdph_mold_enforcement_guide.pdf?1621965061
      2. ↑ https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/mould-and-your-health
      3. ↑ https://aucklandhomeshow.co.nz/blog/bathroom-ventilation/
      4. ↑ https://aucklandhomeshow.co.nz/blog/bathroom-ventilation/
      5. ↑ https://www.epa.gov/mold/what-are-main-ways-control-moisture-your-home
      6. ↑ https://www.energy.gov/sites/default/files/2021-08/ES-HomeVentilation_081021.pdf
      7. ↑ https://www.tenancy.govt.nz/assets/Uploads/files/healthy-homes-standards-ventilation.pdf
      8. ↑ https://www.mass.gov/files/documents/2016/09/qx/780012_0.pdf
      9. ↑ https://youtu.be/dFP8dQsYMU4?t=228
      1. ↑ https://www.energy.gov/energysaver/minimizing-energy-losses-ducts
      2. ↑ https://youtu.be/gvinrSU5vEo?t=9
      3. ↑ https://www.energy.gov/sites/prod/files/guide_to_durable_attics.pdf
      4. ↑ https://www.bhg.com/homekeeping/house-cleaning/tips/how-to-clean-bathroom-fan/

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