Humidity streaks

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Frio39

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I recently renovated my small (about 50 square feet) front bathroom. I painted with a Behr Premium Interior Enamel in satin finish. I installed a Nutone 110 CFM exhaust fan. Everything in the bathroom with the exception of the tub is new, including all new green board, floor tile, wainscoting etc... I am having a problem now with humidity streaks on one wall, mainly at the top of the wall. Should I upsize the exhaust fan with one that will move 150+ CFM ? The bathroom is used by my 19 year old children who obviously take extra long showers. There is no other ventilation in the bathroom other than the exhaust fan. Thanks for any and all advice.
 

JRC3

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Are the children acually turning on the fan when they shower? Usually they do not. Best bet is the have the fan and shower light on the same switch.
 

Frio39

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Are the children acually turning on the fan when they shower? Usually they do not. Best bet is the have the fan and shower light on the same switch.
I would like to say they do everytime but not for certain, I know I have showered in there before with the fan on and it still happened.
 

Jadnashua

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How much of a gap is there underneath the door? The ability of the fan to move air is partially dependent on how easy it is to draw air into the room to then exhaust. If your house is particularly tight, without a window open somewhere (not a great idea in humid FL), it can be hard for the fan to actually push that much air out of the house. You might need something like an Energy Recovery Ventillator

https://en.wikipedia.org/wiki/Energy_recovery_ventilation

If you leave the door open and the fan on, do you still get the same problem?
 

Frio39

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How much of a gap is there underneath the door? The ability of the fan to move air is partially dependent on how easy it is to draw air into the room to then exhaust. If your house is particularly tight, without a window open somewhere (not a great idea in humid FL), it can be hard for the fan to actually push that much air out of the house. You might need something like an Energy Recovery Ventillator

https://en.wikipedia.org/wiki/Energy_recovery_ventilation

If you leave the door open and the fan on, do you still get the same problem?
There is virtually no gap under the door - I havent tried it with the door open. Should I trim an inch off the bottom of the door?
 

JRC3

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Funny, I know this...My recent last house of 14yrs had no gap under the door and I used to leave the door cracked 1/4" because of it.
 

Jadnashua

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A fairly simple, but kind of gross assessment would be to take something light and hold it near the fan with the door open, and then with it closed. It sounds like you'll probably notice a big difference. A smoking candle might also give you an idea of the airflow.
 

Erico

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I would definitely upgrade to a larger fan. 110 is close to the recommended minimum for your space and doesn't account for teenager marathon showers or lack of a window.

Residual moisture and humidity in one thing but this streaks are being formed WHILE the shower is in use. I have a similar problem in my 4x8 little bath even though I have a 110 cfm fan. Part of my problem is floor to ceiling glass tile on all four walls that condensates.

Panasonic has a 190 cfm fan. I like theirs because the fans are quiet. My neighbor bought an 80 cfm that was .3 sones. Almost silent. I went larger for the same 4x8 space with a 110 cfm at .8 sones because I was considering a steam shower(we did a joint stacked condo bath project so I ordered both fans). Some of the big box fans are cheap but sound like busted chainsaws at 2.5 sones when running. My neighbor was all over the quiet factor. I wouldn't have cared about sones if it wasn't for her.

Panasonic even has a 290 cfm fan but that might suck one of the kids up in the vent. :) Also, you may or may not need make-up air in the house if you go large enough. Not sure what the cut off is for make up air but you don't want to suck furnace and water heater chimney gas back in the house. For some reason I remember 500 cfm but don't quote me.

You may not be able to change it now but how the fan is ducted can be part of the problem. Flexible not as good as rigid. More elbows worse than fewer elbows.

What you can change:

Increase fan cfm

Allow more air in. Cut the door up an inch. Also, you might consider through the wall vents. Rather than place ugly vent covers on a door, consider one or more pass through holes in the drywall between studs. 12x12? Or 9x9? You can cover both sides with a flat vent cover. I've done this for friends who got dinged by a home inspector for make up combustion air in a utility closet. I placed the vent up high and turned the the grates so you can't see through in to the wall cavity from ground level. Drawback: lack of privacy - may not be a problem upstairs in a hallway but not so good off a living room or kitchen.

Add a timer. I have mine on a 60 minute digital count down timer from a big box. 20-30 bucks. Honestly, a 120 minute timer might be better. Or if you want to get fancy, a switch with auto moisture sensing.

Tell everyone to leave the door open when finished. I have this argument with my wife. She is worried the dog will get in to the trash can so she closes the door. She leaves at 5am and when I use the bathroom there is still a bit of condensation on the window and walls at 7am. And that's with a 110 cfm fan on 60 minutes. I tell her to place the trash can on the toilet if she is worried. Note to self: buy a trash can with a lid.

If I remember correctly, those Panasonic fans are rated for continual run use. Like 100,00 hours. I think They can be used as home ventilation.
 
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