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Can my air return be preventing my bathroom exhaust fan from drawing air? We have a terrible time with moisture building up during showers. The air return is on the hall wall directly opposite the bathroom door.

Steps we have taken so far:

  1. Replaced the fan with a new fan sized for larger bathrooms (the bathroom is small.)
  2. Trimmed the bottom edge of the door to allow more air in.
  3. Tissue paper test was successful, but I don’t know if the air was running when I did it.

I’m wondering if air flowing along the floor into the return could be too strong for the fan to draw any into the bathroom. I’ve looked for deflectors to try, but need a 30” one (return is 20x30 mounted with the long side horizontal.)

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  • This could also indicate negative air pressure in the house.
    – Gil
    Dec 27, 2021 at 20:04

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You'll never be able to eliminate the moisture problems during showers unless you take cold showers. Even leaving the door open wouldn't solve the problem immediately because the moist air is so much heavier than dry air. You can test your theory about the return stealing the air by turning off the fan in the bathroom and turning on the AC and see if the bathroom fan spins on it's own from reverse flow... probably not in my humble opinion. Just leave the bathroom door open after showering and let the fan run for 20 to thirty minutes. You should also check the fan output where the duct leaves the house to make sure the duct is clear.

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