Inside CR Test Labs: Maintaining an air purifier

How well you maintain your air purifier will directly affect its performance over time

Do you remember the last time you cleaned the filter in your range hood or replaced the filter in your furnace or air conditioner? If no, you're not alone. As part of our testing for "Filtering the Claims," we wanted to see how air-cleaning performance would changes as an air purifier's cleaning media became loaded with dust, smoke, and other airborne particles. We also hoped to determine if you  need to replace filters as manufacturers suggest or if doing so is a waste of money.

To measure how cleaning performance changes over time, we tested the Friedrich C-90B plate-type electrostatic precipitator, or EP, air purifier and the Whirlpool Whispure AP45030S and IQAir HealthPro Plus HEPA-filter models. We ran these air purifiers nonstop for one year in a very large commercial space whose air we expected to contain dust and smoke particles.

We also rearranged the devices in the space to ensure each machine experienced the same conditions. And throughout the year at regular intervals, we brought the purifiers back to our labs to gauge their cleaning performance.

While the performance of the two HEPA models declined gradually and at a similar rate, that of the Friedrich (shown) fell more abruptly—about 20 percent in one month. It took the entire year, including not changing the prefilters at the manufacturers' recommended intervals, for the HEPA models to decline that much.

However, because the Friedrich's initial performance was the best of this group, after a month its absolute performance, indicated by its clean-air-delivery rate, or CADR, was still higher than that of the IQAir when new—265 compared with 237. It took about another month without cleaning its plates before the Friedrich's CADR dropped below 237. What's more, after we cleaned its prefilter and collection plates, the Friedrich saw its CADR return to its original high value of 335, confirming the importance of maintenance.

The bottom line: You need to maintain your air purifier if you expect it to keep cleaning the air in your home. Our testing supports the typical maintenance recommendations from manufacturers. Note that our testing also shows that plate-type EPs generally require more-frequent filter cleaning than filter-based purifiers.

But you'll likely spend more to maintain and run a filter-type purifier than you will for an electrostatic precipitator since the former type normally uses replacement filters and consumes more electricity.

Still, if you're unlikely to perform the necessary maintenance, opt for a filter-type purifier, which we consider your best choice overall because it cleans the air without producing ozone. Research is increasingly warning against adding ozone to indoor air, though more studies need to be conducted to determine the effects of low-level ozone exposure on humans.—Ed Perratore

Essential information: Our Ratings of room and whole-house air purifiers include annual costs for energy and filters or other media. Read our advice on how to improve the air quality in your home without an air purifier.