To Your Health

What is the best kind of air purifier to use in my home to help reduce allergens?

Q. Allergies run in my family, and I want to try an air purifier to see if it helps. What is the best kind: electrostatic or HEPA filter?

A. A growing body of scientific evidence indicates that the air inside homes can be more polluted than the outdoor air. Because most people spend more time inside their homes than anywhere else, it makes sense that indoor air pollution can cause or contribute to allergies. You will need more than an air purifier alone to keep allergy symptoms under control, for homes cannot be made entirely allergen-free, but the major sources of exposure can be greatly reduced.

The choice of air purifier depends on which allergen needs to be removed. You may need the help of an allergy specialist to identify the allergen or allergens that affect various family members, and then choose the purifier that does the best job of removing the most allergens. The most common allergens are rather large particles – such as pollen grains, dust mites, pet dander, and mold spores – which can be efficiently removed by HEPA (High Efficiency Particle Absorbing) filters. However, some allergens are gases such as formaldehyde that pass right through some purifiers.

The goal is to remove the allergens that are provoking symptoms for anyone in the family without the unnecessary investment of either money or time in trying to remove everything. To remove common allergens from the air in your entire home, an electronically enhanced furnace filter in your central-air system can clean the air continuously if you leave the fan on even when you are not heating or cooling. The unit costs less than $300, and the filters, which are replaced every month or two, cost about $60 for a year's supply.

If you think you can get by with just cleaning the air in one or two bedrooms, single-room air filters are widely available in a range of prices. Unfortunately, the most aggressively advertised models, the electrostatic filters without fans, are among the poorest performers, typically removing less than half the particles that the most efficient ones can. These types of air purifiers have the advantage of being noiseless, but even some of the models with fans are not much better. The best of these air purifiers with fans make about the same noise as a refrigerator, but some are definitely noisier, and if you plan to use an air purifier in your bedroom, you will want to get the quietest you can find. Prepare to pay in the range of $500 for the best of these, but you save money by not needing to use filters.

If it turns out that you must remove a chemical like formaldehyde from building materials or urea-formaldehyde insulation or some other volatile organic compounds released from carpet, house-cleaning products, paint, etc., you will probably need to use an air purifier with an activated charcoal filter. Compared to a HEPA filter that should last two-to-four years, charcoal filters last between six and 12 months and may cost $50-150 to replace. The least expensive of these air filters for a single room will be about $350, and some models cost more than $1,000.

Only about 5% of people with allergies suffer with sensitivity to chemicals, but for that population, the charcoal filters are an immense benefit. If your allergy symptoms are seasonal, or if you know that your allergens do not include volatile organic chemicals, the electronically enhanced whole-house furnace filter may be sufficient.

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