Does the Furnace Filter Block Ozone?

Charcoal Filters

• Charcoal filters, or activated carbon air filters as they’re also known, are capable of removing gases like ozone as well as common household odors such as cigarette smoke, garbage and pet odors. The carbon air filter is incorporated into the pleated air filter design, which is the most common furnace filter available. Look for a carbon furnace filter with a MERV rating of 8 or higher.

How They Work

• Activated carbon is usually made from coconut shells that have been heated under pressure to over 2,000 degrees C. This process causes millions of tiny pores to form, increasing the surface area of the carbon to the size of a football field, if it were flattened out. Ozone particles that pass through the filter are trapped in the pores. Over time, some of the trapped ozone slowly “bleeds off,” allowing the filter to absorb more contaminants. Eventually, however, the filter needs to be changed.

Changing

• A dirty filter isn’t able to remove ozone and other pollutants from the air and it can make your furnace overheat and stop working. Check your furnace filter every month during the heating season and change it if necessary. Turn the furnace off before you change the filter. Look for the marking on the old filter that shows the direction of airflow, and use a permanent marker to copy this marking to the outside surface of the duct or some other flat surface nearby. This marking will let you know which side of the new filter should face the furnace.

Effectiveness

• According to the Environmental Protection Agency (EPA), even though properly designed and maintained charcoal filters do effectively remove ozone and other pollutants from indoor air, they can’t remove all pollutants from the air. For instance, charcoal air filters don’t remove carbon monoxide. In addition, according to the EPA, the filters may release pollutants back into the air once they become saturated. Carbon filters can range from 1/8 inch to 2 inches thick and weigh anywhere between a few ounces to several pounds. When shopping for a good carbon filter, look for one that is several inches thick, or one that is heavy, because they will more effectively remove contaminants.