I moved your thread to the "AOP Residential HVAC (Beenthere Zone)" forum as this is the only place where homeowners can ask questions.

Please take note of this new location as the "Moved" icon in the other forum will only last a day.

 

Just noticed that and I was getting ready to move it. Sorry and thank you!

 

Bump.

 

72sqft isnt very large.
Excess steam / humidity in the room from long hot showers can be partially controlled by a quality extraction bath fan, but since the room has no outside air return, all the fan can move is the extra vapor feom the shower operation.
To get good control of system, there needs ro be a complete airflow circuit.
Air being pumped out of the room needs to have equal amounts of air pumped into the room from the same place the air is being pumped to from the room.

Meaning if air gets pumped outside, outside air needs to be replaced into the room.
Erv/hrv can be setup to perform this, or a dedicated dehumidifier can be tied into the room...

 

Here is what I find interesting. My wife took a shower this morning with the door cracked and mirror fogged up. I took my shower 1.5 hours later with the door fully closed and no fog at all on the mirror. How the heck can that happen?

I can assure you that our house was not built tight at all. We do have a house wrap, but all of the walls are R-11 bat insulation. The bathroom is located at one of the bump outs on the second story.

 

Do you set the house temperature differently night versus day?

What was the outdoor temperature for her shower versus the outdoor temperature during your shower?

Is the mirror located on the outside wall of the bathroom?

Which compass-point direction does the bathroom bump-out project toward?

Is the mirror mounted on a recessed cabinet?

Perhaps her mirror was colder and your mirror had had time for it's temperature to increase to above the dewpoint?

Perhaps she sets the showering water temperature higher than you do?

PHM
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Today was another interesting shower day. I took a slightly longer and warmer shower today with the door closed. When I finished the half of the mirror closest to the shower was fogged up, but the other half was perfectly clear.

 

Mirror fogging is based on wall / mirror temp… and stratification layer of the moisture.

 

That hypothesis crossed my mind last night. Decided to override the thermostat to keep the house at a constant 67 degrees Fahrenheit instead of dropping iIt to 64. I need to get a laser thermometer to see what my wall temps are.

 

What is the temprature of your house?

When I bought my home it only had wall heaters and no bath exhaust. Mirror would always fog up. After installing central heat/cooling, and a bath exhaust fan, here's what I do:

If the home is 70*F or warmer, I only need the bath exhaust. If the home is 69*F or cooler, I turn on the central heat while I am in the shower. Works great for me.

I later added a humidity stat and have it set a bit over 50% RH, it comes on once in awhile. Probably more often if someone else takes a shower and does not understand about turning on the central heat for a bit while taking a shower.

 

Temp usually drops to 64 for sleeping around 10pm and jumps up to 68 around 5am.