Bathroom fan ventilation inadequate

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  #1  
Old 11-23-14, 10:17 AM
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Bathroom fan ventilation inadequate

I've recently renovated my bathroom. It is about 75-80 square feet (12 feet by six feet), rectangular in size with the bathtub/shower placed crosswise at the far end of the room from where the door is.

Previously, the bathroom fan was located more in the middle of the room; however I wanted to relocate the bathroom fan into the shower and use a fan/light combination.

I installed the new fan (Air King BFQF70) at 70 cfm directly in the shower.

I also installed a new ceiling (smooth painted versus the old popcorn texture) and repainted the walls.

Upon finishing the project, we noticed within a week that condensation was accumulating on the ceiling and upper walls, and then running down the walls, leaving ugly streak marks. I tried washing and repainting the walls, then letting the paint fully cure for a week before operating the shower. Problem recurred.

I upgraded to a 120 cfm fan and while this slows the condensation process down, the streaks eventually come back.

I do like hot, steamy showers, but I've never had a problem like this before with my old bathroom set up. I feel 120 cfm should be more than adequate for this size room.

What am I missing here?

Thanks in advance for any advice.
 
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Old 11-23-14, 11:36 AM
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Welcome to the forums!
What am I missing here?
Leaving the fan to run at least 30 minutes after you finish your shower with the door open. The fan can't handle all the moisture and air at a short interval. You need replenished air to keep it at equilibrium.
 
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Old 11-23-14, 12:07 PM
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The problem happens during the shower. When I get out of the shower, I can already see the condensation on the walls. The fan is on a timer and runs for 15-30 minutes after I finish.

I could leave the door open when I shower but I never had to do this before with the old fan. There's also a window (well insulated) int he shower that I could open a bit?
 
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Old 11-23-14, 12:13 PM
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Is the fan actually functioning properly? Where does it exit the house? Have you checked for air flow from the outlet end? What size duct is being used? Is it corrugated or smooth bore?
 
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Old 11-23-14, 12:53 PM
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The fan appears to be functioning properly (I've tried several fans as well within the same housing). I just went on the roof and there is lots of air blowing out.

It's 4" plastic hose. There is some corrugation to the hose as it's wire reinforced plastic, but the plastic is quite smooth.

Is it possible that the paint is the problem, or the fact that the ceiling is smooth and not a popcorn ceiling?
 
  #6  
Old 11-23-14, 01:24 PM
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When your fan was centrally located, it caused air movement throughout the room. This reduced or prevented condensation on the walls and ceiling. With the fan in the shower, it pulls the warm, moist air from the shower, but some vapors escape into the room and cause the problems you are seeing.
 
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