Let's talk about the evolution of bathroom vent fans. Before we do, though, I think it's important to point out that bath fans aren't just to keep the room from feeling steamy or to ensure that you can see your pretty self when you get out of the shower. They're actually really important for maintaining the integrity of the materials in your home.
Many older houses don't have bath fans at all, which is okay if the room has an openable window (on the theory that the occupant will open the window to allow steam to escape even in the dead of winter). Other houses have fans that vent into the attic space, which is wrong, wrong, wrong. (This allows moisture to build up in the attic, where it can get trapped and turn your roof decking and insulation into a soggy, moldy mess.) The only proper installation of a bath fan is one where the duct leads to outside air. In most cases, that's up through the roof, but it may also be to an exterior wall or, in our case, up through the attic and out at the eave. (I wouldn't want to put it at the eave if the house had soffit vents -- which would likely just suck the moist air back into the attic -- but our sealed attic doesn't.)
We have a few different kinds of vent fans. Some of them are standalone units that have a plastic grate against the ceiling (which can also be installed in a wall). Others are disguised in light fixtures. Of those, there are a couple built into recessed lights, and the one in the front bathroom is hidden in a not-bad-looking ceiling-mounted fixture:
But there's another feature that sets two of our vent fans apart from the others. One ceiling-mounted standalone fan and one recessed light fan have built-in humidistats. This kind of fan is designed to be left on all the time, and when the shower is turned on, the humidity level will rise and turn the fan on automatically.
Unfortunately, this hasn't really been our experience. The fan in the master bathroom, which we have used the most, doesn't always come on when we shower. Sometimes it doesn't come on until five minutes after we turn the shower off (long after the humidity should have triggered it). Sometimes it comes on when it should but stays on for three hours. Sometimes, if we leave the switch turned on -- which we try to avoid -- it comes on in the middle of the night, waking us up. Our builder has replaced the unit, but the new one has all of the same issues. The sensitivity is adjustable (through a dial that, unfortunately, can only be accessed by removing the guts of the unit from the wall), but making it more sensitive would seem to worsen the nighttime wake-up calls and making it less sensitive would probably make it even less likely to come on during showers.
The builder is waiting to hear from the vent fan manufacturer for a solution, but I'm not hopeful that there's going to be a way to get these fans working for us. My suspicion is that this technology just isn't there yet. It's a great idea -- forgetting to turn the fan on won't result in moldy drywall, and forgetting to turn it off won't waste energy -- but it just isn't working. D-.
Stay tuned tomorrow for a much better solution for bathroom vent fans. (Spoiler alert: I give it a solid A.)