You may be using your air purifier incorrectly.

What I’m saying is If I were to visit your home, which I would do, I might look around to see if you have an air purifier, and if so, estimate the square footage of the room, and when I’m alone, I might open it up and check the filters.

I know I’m a bad customer, but I’m doing my best for the greater good.

Depending on what you find, resist the urge to tell them that their air purifier is too small to clean the room effectively, that they shouldn’t put it next to the couch or a wall, that their filter needs to be replaced, or worse, that the plastic covering the filter was never removed when they bought the air purifier.

The urge to give unsolicited indoor air advice runs deep. Before I took on the role of air quality, I didn’t know much about it. I never thought about it or understood that making a few changes or using a tool or two can have a lasting impact on our health, the quality of our sleep, and our intelligence. And I wish the same for you. Be sure to check out our related guides, including the best air purifiers, the best indoor air quality monitors, and the best robot vacuums.

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Size matters

You may already have an air purifier. Is it the right air purifier for your room? I used to think that a small, beautiful air purifier was enough. But now it’s different.

First, find out how much space your air filter is sized to cover, and understand that air purifiers are often sold with the advertised space capacity at their highest setting — and remember, that’s also the loudest setting.

You probably aren’t blasting your air purifier hard, so what’s the square footage of the setting you normally use? Then, find the formula: How many air changes occur in an hour in a room of a certain size?

The ideal number is called the Clean Air Delivery Rate (CADR) and can be found on the air purifier’s label. The higher the number, the larger the room it can clean. Keep in mind that CADR is based on a room with an 8-foot ceiling height. If you have high ceilings, like an A-frame, you’ll need an air purifier with a higher CADR.

The right fit for the right speed

Once you have your CADR, you’re not done – there’s still more work to be done to optimize your air quality. For example, if you use an air purifier in your bedroom, “sleep mode” means that your purifier is running on its lowest setting.