To clear the air, clean your air purifier filter An air purifier can't do its job if the filter is dirty

Consider an air purifier as a last resort after you’ve done everything else you can do to improve your home’s air quality, such as banning indoor smoking, banishing pets from bedrooms, and vacuuming often. But if you still think you need a portable air purifier, keep in mind that there’s more to owning one than plugging it in and switching it on. Routinely cleaning or replacing the filter should keep your model doing its job for years.

Most of the air purifiers in Consumer Reports' tests have a filter indicator that tells you whether a part of the purifier needs to be cleaned or replaced. The challenge is that many of today’s air purifiers use a few different technologies. In addition to a pre-filter, which is usually cleaned rather than replaced, you’ll occasionally need to replace the HEPA filter and perhaps a carbon filter. We include these expenses in the annual costs we list in our ratings. Check your manual for other maintenance requirements, especially for more advanced models.

One more point about filter indicators: While some newer air purifiers might tell you it's time to clean or replace a filter based on how much you’ve actually used the unit, some others base their recommendation on time alone. So if you run your purifier less often, you might prefer to visually inspect at least the HEPA filter before tossing it to keep from replacing filters unnecessarily. That’s also what you need to do if you replace the filter on your forced-air heating/cooling system with a denser one designed to filter out dust and smoke in circulating air, such as the $20 Filtrete Healthy Living Ultimate Allergen Reduction 1900 MPR. Such replacement filters have no way of indicating that they’re getting clogged.

If you’re shopping for an air purifier, check out our Ratings of 40 portable room and whole-house (labeled home) air purifiers. Among top-scoring portables are the $250 Honeywell HPA300 and $300 Whirlpool Whispure AP51030K. Our air purifier buying guide will give you a rundown on the latest advances in this category.

—Ed Perratore (@EdPerratore on Twitter)