My family and I are paranoid about a poorly-ventilated bathroom, so we religiously run the exhaust fan during and after showers. With busy lives and kids to take care of, this often means walking away from the bathroom right after a shower, with the fan still running.

On weekends I would occasionally come upstairs mid-afternoon to find the fan running from a morning shower. Some evenings I would come home from work and find that the fan had been running all day. In a previous home I installed a digital fan timer to remedy this problem. However, a moisture-sensing fan switch is a more elegant and appropriate solution. It also costs about the same as a digital timer, and the labels on my old timer wore off after a year or two. I have had this moisture-sensing switch installed for a few days, and without fail it turns on during a shower event. In some cases it comes on mid-shower, in some cases it comes on AFTER the shower is turned off, and in at least one case it has turned on post-shower, turned off, and then turned back on again. This gives me the confidence that the humidity sensor is working and is responding well to changing conditions. It's nice to be able to walk away from the bathroom after a shower and know that your home is being taken care of.

This device does require a neutral connection as well as the typical hot, load, and ground. For me this wasn't a problem, but if the power comes in at your fan and not at your switch box, and your switch box has only a switch leg, this device won't work for you.

I wanted to install a humidity-sensed fan switch in my bathroom, so I can forget the fan for ever. However, this product failed this minimal test. I set the humidity trigger to around 50%, Sensitivity to high, and time duration to 20 minutes. I hoped the fan would kick in while I am taking my shower. 5 minutes, the fan was not on. 10 minutes, not ON. 15 minutes, not ON. When I finished my shower, the mirror is condensed with water, and the fan is still not ON. What's the point getting this product????

Update: one reviewer mentioned that the humidity sensor may not work properly if your switch wire box has draft. I have caulked the surrounding of the wire box, and put a foam pad between my light switch and this fan controller. It helped but still not sensitive enough. I set humidity to 30-40%,high sensitivity. Still the outcome is quite random. I changed my review to 2 stars

I studied up on the available humidity switches and decided on Leviton based on the features and price. I'm happy with my purchase.

1. The timer is great, which can be set at 10 min, 20 min, 30 min and 45 min. The fan will run for that set time and turn off, or you can still manually turn off any time.
2. The humidity set point can be set for Off or any range between 20-80% humidity, and also an Air Cycle mode. When using Off it'll ignore the humidity set point and run when it detects excess humidity. I'm not sure if that means it'll detect an average of the current humidity level and only turn on if it increases above that average. I set mine at about 40%. Air Cycle will run the fan for the timer duration once every hour, nice if you need constant air flow regardless of humidity.
3. The sensitivity levels. Off, Lo, Med and Hi. Off is for Air Cycle mode only since it runs based on the timer not the humidity. Lo Med and Hi sensitivity levels have two uses each. Lo is for small spaces but also the least sensitivity, and so on for Med and Hi.

My bathroom is about 6 ft x 6 ft. I have my timer set for 10 min, humidity at about 40% and sensitivity on Lo. I live in Colorado so our humidity inside is usually around 30%. So far this setup is working perfectly, I turn the shower on and within about 2 minutes the fan turns on, then turns off about the time I get out. It might turn itself back on again if there's still too much humidity then shut off after another 10 mins. I have not had this randomly turn the fan on when not using the shower. This is exactly what I wanted to prevent mold and prevent manually touching a switch.

My fan and light are separate units but this switch can also be wired to a fan/light combo. Only problem there would be using the timer since it would also turn the light off. Regardless of that, you will need a neutral wire (usually white sheathed) for electricity return. This switch will not operate correctly without a neutral wire, it'll remain on all the time without it because the power has nowhere to return to. Most switches these days need neutral which is a good thing for safety. If your house was built in the 90s and newer, then you should have neutral wire capped in your switch boxes even if your current switch doesn't use it. It's easy to add a connection to that with more 14 gauge copper wire.

Edit: I changed the sensitivity level to Med. There's a vent directly below the switch and noticed on Lo the switch wouldn't activate if my furnace blower fan was running.

Update, a few weeks later: Now the switch won't turn on the fan regardless of the humidity settings. My wife said it still works for her but she didn't even want this switch. So I'm dropping my rating on this from 5 star to 3 star because it was for me and my peace of mind. At least the timer still works well.

Update, another few weeks later: Since my last update its been working well so I'm changing my review from 3 to 4 star. I won't take it back to 5 star, just in case.

I was really happy with the using out of the box settings in a master bath. It worked fine all summer even with the short ten minutes default timer.

But when the temperature dropped and the heat came on this started tripping all the time. I had to remove the switch plate and cover and extend the timer and drop the sensitivity from High to Medium and it seems fine.

I don't know if I will need to change things back when we go from heat to cooling.

The device works great but I wish I had more control.