How to Reduce Moisture on Bathroom Walls

I have two vent fans in my bathroom; and after a long, steamy shower, I’m still getting water and stains on my walls. How can I fix this problem? -Phil

Hi Phil,
You can’t expect prolonged exposure to a room full of steam not to condense on your bathroom walls, so start by cutting back on the length of your shower and lower the water temperature. A bathroom vent fan isn’t designed to remove all steam in a matter of seconds; so you have a confined space that’s filling with steam faster than one, or even two, fans can pump it out.

Here are some tips to improve the performance of your exhaust fan in removing moisture from the bathroom:

  • Turn the vent fan on before you start your shower, and let it run for 20 minutes after you finish your shower. Installing a timer switch or humidity sensing fan is a good way to make sure you run the fan long enough to clear the air after a shower.
  • Make sure the exhaust fan vents outside through a wall or roof. While nonventing fans are available for removing odors, they’re not designed to lower the humidity in the room.
  • Check the vent duct to make sure the flow of air isn’t impeded, and the duct is as short as possible with few turns.
  • Make sure you have enough fresh air entering the bathroom either through a gap (5/8” or more) under the door, or by leaving the bathroom door cracked when the fan is in use.
  • Be sure your exhaust fan has enough capacity for the size of the bathroom. To calculate the size fan you need in a bathroom with an 8’ ceiling, find the square footage of your bathroom (length x width) and install a fan with at least that capacity in cubic feet per minute (CFM) or more. Example, for a 5’x 10’ bathroom, you would need a fan rated at 50 CPM or more. For bathrooms with taller ceilings, multiply the cubic feet of the bathroom (length x width x height) by 0.13, then choose a fan with that CFM or higher. Example: a 10’ x 5’ bathroom with a 10’ ceiling would by 10 x 5 x 10 = 500 cubic feet, 500 x 0.13 = 65, so you would need a fan with a capacity of 65 CPM or more.
  • Finally, make sure you purchase a good quality fan. Pry open the pocketbook and spend the cash to get a fan that will move enough air and last longer.

Good luck with your project,


Further Information


  1. It was such a relief to read the beginning of this article. I installed a new bathroom fan motor, it works great but yes the walls are steamy. But leaving the fan on for 20 minutes helps. But my worry is mould, will mould collect on the wall?

  2. Install a shower dome and the steam problem is eliminated. Keep the shower door closed after showering until all the steam has condensed then leave it open to dry the shower out.


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