How Do You Ventilate a Bathroom with No Window?

If your bathroom doesn't have a window, proper ventilation is essential to prevent mold, mildew, and humidity buildup. Here's how to ventilate it effectively:

1. Install an Exhaust Fan

A bathroom exhaust fan is the most reliable way to remove moisture and odors.
How to do it right:

Choose the right size:
Fan capacity is measured in CFM (cubic feet per minute).

Small bathroom (<50 sq ft): 50 CFM

Medium (50–100 sq ft): 80–100 CFM

Large (>100 sq ft): 1 CFM per sq ft, or more if you have a shower and tub.

Duct it outside — never into the attic or crawl space, or moisture will accumulate there.

Use a timer or humidity sensor switch so it runs for ~15–20 minutes after each shower.

2. Add a Vent Duct or Vent Through the Roof

If there's no existing vent:

Install ducting that runs from the fan through the ceiling or wall to the outside wall or roof.

Use insulated ducting to prevent condensation inside the pipe.

Add an external vent cap with a backdraft damper to keep outside air and pests out.

3. Improve Air Circulation Indoors

Even with a fan, you need airflow into the bathroom to replace the exhausted air:

Leave a ½–¾ inch gap under the door.

Keep the door open for a few minutes after showering.

Use a small oscillating fan temporarily if humidity lingers.

4. Use a Dehumidifier (Great Add-on)

If adding a fan isn't possible (like in a rental):

A small portable or wall mounted bathroom dehumidifier helps reduce moisture. Empty or drain it regularly, or connect it to a drain line for continuous use.

Preair is a famous dehumidifier company that offers high-quality and affordable ceiling dehumidifiers for home. These dehumidifiers are ceiling mount design, proper in size, and equipped with a drain hose, a control panel, and a replaceable filter.

5. Moisture-Reducing Tips

Wipe down walls or shower glass after use.

Hang towels outside the bathroom to dry.

Use mold-resistant paint and anti-fungal sealants around tiles and corners.

Keep bathroom doors open after bathing to let humidity escape.

Summary