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[quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous]Something else is going on.

Let's say it's a big bathroom and it's 200 square feet. With eight foot ceilings that's 1600 cubic feet. A minimal exhaust fan will exhaust 100 cubic feet per minute, so in 16 minutes it will completely exchange the air in that room. Changing the air should get rid of all the humidity.

[b]My bet is the exhaust fan isn't actually working. It happens all the time that the exhaust gets blocked, the vent on the outside gets painted shut by painters or the hose gets pinched in the wall or something builds a nest in it. It also happens all the time that it was never hooked up properly to begin with. It can also happen that the fan blade breaks and even though the motor is turning it's not moving any air. If you light an incense stick under it it should easily suck all of the smoke out of the room.[/b]

The other possibility is there's another source of humidity other than the shower -- most likely a plumbing leak somewhere. But I'd check the fan first. [/quote]

DH and I checked on whether or not it was actually working. The exhaust butts up against an exterior wall, so we went to the back of the house where the exhaust "exhausts" out, we could feel the air coming out. It felt quite surprising how much air was coming out, it felt like a fan.

The bathroom is about 125-150 sqft. The window is inside the actual shower stall, as is the new exhaust fan. Just like in this image: 
[img]https://www.homeadvisor.com/r/wp-content/uploads/2016/08/3838496_original.jpg[/img]

[/quote]

OK, let's do some science. You've got about 1000 cubic feet of air in that room. At room temperature air weighs about 0.075 pounds per cubic foot so that's about 75 pounds of air. Moisture content of air is measured in grains per pound, at saturation at 75F the moisture content of air is 131.7 grains per pound, so there's about 10,000 grains of water in the air. There are 7000 grains in a pound so that's about 1.5 pounds of water, which is about 24 ounces. You want to get the humidity down to around 50%, which means removing half of that humidity, or 12 ounces or 3/4 pint.

Option 1 is to remove that humidity by replacing the air in the bathroom with air from somewhere else that contains less moisture. That's what the fan does, it exhausts the bathroom air and replacement air comes from either the rest of the house or outdoors. With 1000 cubic feet in the room and a fan that does 100 CFM ten minutes should replace all the air. Note that running the fan while the shower is running doesn't really do you any good, the shower can probably put humidity into the air faster than the fan can remove it. It's ten minutes after the shower stops that you need.  And it has to be really exhausting the air. It's incredibly common for bath fans to be hooked up wrong, probably more common than not. Even if it's running and creating suction it could be just dumping the air back into the room.

Option 2 would be to run a dehumidifier. A popular size is rated for 72 pints per day or 3 pints per hour, if you need to remove 3/4 that's 15 minutes worth of dehumidification. Again, it has to be after the shower stops.  You can look at how much water is in the tank to see how much it's removing.

If one or the other of those two steps  -- removing all of the humidity in the air -- doesn't work, then you need to consider the possibility that something else other than the shower is your source of moisture.

[/quote]

Wow! thank you for taking the time to fully explain this! Okay so we need a larger dehumidifier for sure instead of the punie one we purchased.  One thing that I guess I should have mentioned but didn't is that this bathroom does not have an HVAC vent.  When we did our whole house remodel two years ago we requested that the contractor put one in, he did not. That's another story for another day.  I mentioned to DH yesterday that I thought not having an HVAC vent in there was not helping matters, and it seems like this is an accurate observation. So really our only option is option 2!

Thank you again! [/quote]

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