How do air purifiers work?

Air purifiers usually consist of a filter, or multiple filters, and a fan that sucks in and circulates air. As air moves through the filter, pollutants and particles are captured, and the clean air is pushed back out into the living space. Typically, filters are made of paper, fiber (often fiberglass) or mesh.

What is a HEPA filter?

HEPA is an acronym for High Efficiency Particulate Air. HEPA Filter capture variously sized particles within a multi-layered netting usually made out of very fine fiberglass threads (much thinner than a strand of human hair!) with varying sized gaps. The filter is composed of a dense sheet of small fibers pleated and sealed in a metal or plastic frame.

The air purifier's fan draws air into the filter and particulates are captured in the filter. The larger particles (ones bigger than the fibers) are captured via impaction (the particle crashes into the fiber), mid-sized particles are captured by interception (particle touches the fiber and is captured), and ultra-fine particles are captured by diffusion (while zig-zagging the particle will eventually hit and stick to the fiber).

So… should I buy an air purifier?

Before you do, know that an air purifier is not a cure-all. . That’s due in part to the fact that it is difficult to separate the effects of known air-quality pollutants in your home from other environmental and genetic factors. (For instance, how are the furnishings and ventilation in your home affecting you in addition to any indoor pollutants?) But if you are an allergy or asthma sufferer, an air purifier with a HEPA filter may be helpful for you as it will be good at removing fine airborne particles.

What should I look for in an air purifier?

• CADR (clean-air delivery rate) rating. This measures the cleaning speed of the purifier for removing smoke, dust and pollen.

• Size guidelines. For proper efficacy, you need a model that will work for your room size. Choose a model that is designed for an area larger than the one you are outfitting it for if you want to operate it at a lower, quieter setting.

• True HEPA. True HEPA filters are effective at removing ultra fine particles (think: dust, dander, pollen, mold and other common allergens in the home). The industry standard is that the unit must be able to remove at least 99.97% of particulates measuring 0.3 micron diameter in a lab setting.

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What are other ways I can improve the air quality in my home?

The best advice is to address the source of indoor air pollution and to ventilate your home. If you are looking to supplement the work of your air purifier or see if you can get by without one, we recommended trying these steps to help reduce indoor air irritants:

1. Keep your windows open when it's safe to do so to prevent locking irritants into rooms (especially when air purifiers aren’t running!). Create a stronger cross draft by opening windows on opposite sides of the room if possible.

2. Vacuum often. If you are in the market for a vacuum, opt for one that is sealed, has a bag and is HEPA-certified. They’re better at trapping dust instead of sending it back into the air.

3. Regularly change air filters to properly maintain HVAC equipment and maximize effectiveness.

4. Use an exhaust fan in the kitchen (and bath and laundry areas if possible). Switch it on before preheating the oven or firing up the burners, and leave it running for a few minutes after you’re done cooking.

5. Minimize the use of candles or wood fires and ban smoking inside the home. Reducing pollutant sources is a surefire way to improve air quality.