And I agree, I dont check a thing in the morning before my shower. My phones off, I get out of bed and shower. And for all these years of home ownership, have always ran the fan.

As well, try explaining this to your family and have them track the weather to use the fan or not? Or guests as well. Lets be honest, it wont ever happen.

I am huge into humidity mitigation in my house. I have remote gauges all over the house I keep my eye on alot. I mean a bathroom fan may cause a negative pressure and bring in the outside air, which may be as humid. But its all over the house, not just one room.

In winter here when it gets cold, we are supposed to have 15% humidity at -35 Celcius. Can it be accomplished, very hard to do. Ive been close, 20%, and it was so unbearably dry in the house, it just wasnt feasible. Plus with the low of a humdity you run other health risks. So you save you house, and risk your personal well being. Theres science, and then theres “real life”

While this all makes sense, lets face it, its not a fucntional way to live.

I enjoy the psychrometric analysis for bathroom ventilation, but in the end I just use simple observations based on trial and error. In the winter when I know the heating system is running a significant amount of the time, I don’t use the bath fan because the additional humidity is generally useful. In the summer when I know the cooling system is running a significant amount of the time, I also don’t use the bath fan because I know the cooling system will remove the additional humidity. During mild weather conditions when there is not much heating or cooling operation, I do use the bath fan. If water is condensing on any surfaces during any season, I use the bath fan. This is the part that I learn through trial and error. I do keep a cheap temperature/humidity sensor in the bathroom to be sure that the relative humidity is not getting too high.

I could develop an expensive control system to do all of this, but no one would buy it 😉

I used to work for Carrier and learned a little about their history. Willis Carrier’s first AC system just sprayed chilled water into the air stream which would then cool and dehumidify the air. I am guessing that it also helped clean the air. This was used in textile factories where humidity control was important.

Sounds nice but if you live in Texas there is no cold water in summertime 😂

I am west of Fort Worth which is quite a bit hotter than Dallas. If you are familiar with the area 360 is the dividing line and there is a reason they say that Fort Worth is where the west begins. Sadly the official chamber of commerce weather station is by 35C at DFW airport (Technically Fort Worths airport if you know it’s history) which is always cooler in the summer and warmer in the winter than where people actually live.
I’m also by the lake and have allot of oak trees which helps make our microclimate different than others. Also the rain generally goes around this area so everything is dry crunchy and bare dirt so the temps go up more here as well.
I would like to see Allison do some research on the impact of yard type in regards to heat. A property with a nice green yard is cooler than one with a zero scaped yard. I see aero scaping doing nothing but causing the heat island effect to increase exponentially. That cooler air around the house also lessens the load on the condenser…

FYI I go by my weather station and others around me to make sure it’s in the ball park.

When we vent a bathroom after a shower, we’re not interested in temperature, for the most part. We’re interested in moisture and all this dew point stuff is cool, but non-intuitive. Give me a gadget that will display humidity ratio (pounds of moisture per pound of dry air) for outdoors and indoors. Then I will ventilate, or not.

Then it’s also not obvious where this gadget should be located. In the bathroom? In the hallway outside the bathroom? In the walk-in closet if connected to the bathroom? I get uncomfortable with non-deterministic paths for infiltration, and so it’s always fan on, window open for me.

Charlie: The more water you send down the drain, the less there is to evaporate into the air.