The Whole Truth

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Merely heating and cooling your household air apparently isn’t enough these days for some manufacturers. The green-building movement has placed much attention on indoor air quality issues and allergy-control, and industry experts expect an increase over the next 3 years in the sale of high-efficiency whole-house air purification systems that work with central heating and cooling systems to filter out bacteria, mold and other harmful particles.

Although there’s little independent, standardized testing to support the health benefits of these systems, in the past 2 years manufacturers have developed higher efficiency whole-house air purification systems that, they claim, can capture up to 99.97 percent of all airborne irritants and even kill viruses, such as H1N1. Assuming that that’s true, that would make today’s products light-years ahead of the disposable blue fiberglass filters that most furnaces used to clean air. Those filters cost as little as 99 cents each but capture—at best—15 percent of the dust that passes through them.

Such improvement is particularly timely, because Environmental Protection Agency is re-evaluating its decades-old standards for acceptable levels of airborne pollutants. And because today’s homes are sealed better than they used to be and thus waste less heat or cooling, indoor pollutant levels now can be higher than those from outside, because cooking fumes, tobacco smoke and household chemicals can build up.

CHOOSE YOUR WEAPON. Whole-house air purification systems can be grouped into one of two subcategories: media filter cabinets, which move air through a filter that must be replaced every few months, and electronic air cleaners, which apply an electric charge to trap irritants on plates or filter-like grids.

Media filter cabinets tend to be much less expensive than electronic air cleaners: About half of the models cost less than $300. Electronic air cleaners cost an average of 60 percent more, but the units can snare more than 90 percent of particles, particularly those that are smaller than 1 micron in size, according to tests by American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). However, most electronic air cleaners produce more ozone than Food and Drug Administration recommends for allowable discharge. In the past 2 years, Carrier, Lennox and Trane introduced ozone-free models, but they cost at least $1,000.

“I would never recommend an air cleaner that generates any ozone,” says Jeffrey Siegel, who is an associate professor at University of Texas and an air-quality expert. “The people who make the devices that emit ozone say, ‘We don’t know whether there’s any harm.’ To me, that’s a much weaker argument than, ‘It’s doing any good.’”

Lennox also now includes as standard ultraviolet lights in its electronic air cleaners. The good news is that 3 years ago, a UV lamp might have been a $400 to $700 add-on. The bad news is that you have to pay at least $900 to buy such a model from Lennox. Manufacturers claim that UV light can kill bacteria and viruses, but you should take that claim with a grain of salt. No study has addressed UV light’s effect on disease transmission in residential homes.

“UV light does cause some sterilization when it comes in contact with certain micro-organisms, like a virus,” Siegel says. “But the real world is pretty complicated. In some systems, a particle may not spend as much time under the light.” So, it might not be zapped.

TOP RANKING. Although the performance of any whole-house air purification system will vary depending on the quality of air and the placement and type of air ducts in your home, ASHRAE tries to rate their effectiveness by MERV, or minimum efficiency reporting value.

A model that is rated MERV 6 (the bottom of the scale) will capture the overwhelming majority of airborne lint, dust, dust mite debris, pollen and mold spores, ASHRAE says. A MERV 11 unit also will be effective against smoke, pet dander and auto emissions, while a MERV 15 model also will capture most bacteria.