Cleaning your bathroom may not be your favorite household chore, but at least it’s pretty straightforward. In fact, you probably have some sort of routine down pat: Putting cleaner in the toilet to work its magic while you clear off the floor and counters, giving everything a quick-but-thorough wipe-down, running the vacuum through the room, and then giving your toilet a final scrub. (Or something like that.)

And while that’s great to do on a regular basis, you also want to give your bathroom a deep-cleaning every so often, where you tackle any problem spots in the tub or shower, wash the floors, and really get into the tiny nooks and crannies that collect dust and dirt. But even doing that, you still may be missing a crucial part of your bathroom: The exhaust fan. Here’s how to clean it.

Because its job is moving air around, it may seem like your bathroom fan should be self-cleaning, but alas, it’s not. In addition to flushing out malodorous air , exhaust fans also remove steam from hot showers and baths and any other excess moisture from the room, preventing (or at least reducing) the growth of mold and mildew.

But, like the rest of your home, bathroom exhaust fans are prone to getting dusty and dirty over time, which can block the grates in the cover, and prevent the fan from doing its important job. Cleaning your bathroom exhaust fan takes a little bit of effort, but the good news is that you usually only need to do it once or twice a year (depending on the dust levels in your home).

The whole process should take no more than 20 minutes. Here’s what to do:

Now that your bathroom exhaust fan is clean, don’t forget to use it every time you take a hot shower or bath, and then for about 20 minutes after —or until the room is no longer steamy.