Buying a room air filter

Amy Musser

I’ve had a lot of friends reach out recently asking about room air filters and whether they should buy one as a strategy for the COVID pandemic. In this blog, I’ll put together my current advice on how to buy a room air filter.

First, should you buy one?  Well, there’s just a lot that we don’t know about this virus.  We know that it is spread by large droplets (which typically travel about 6 ft but can be carried further by moving air under some conditions) and scientists suspect that it can also be spread by smaller aerosols that stay airborne for a longer time.  But no one is sure how much of the spread can be attributed to each mechanism.  Or how much of the spread is related to touching things and then touching your face.  So, a room air filter isn’t a guarantee.  It’s not a substitute for hand washing or social distancing or masking.  Don’t spend your food money on it.  But for people who are in situations where they have to be in the same room with another person, I think we’re at a point where they are a sensible addition to our safety protocols.  This might include massage therapists, college students living in dorms or apartments, and people who have to have one on one office meetings.  

If you are going to buy one, what should you look for?  There are 3 main criteria that I would recommend applying:  (1) look for one that does a good job of filtering small particles, (2) look for one that has been tested by someone and that appears to have been on the market for a while before COVID existed, and (3) make sure that the unit you buy doesn’t generate significant ozone.  I’ll share a few resources that will help you do this.  

The most widely available “small particle” rating is typically for particles 2.5 microns or smaller (often called PM 2.5).  A medical-grade filter that removes even smaller particles (like 0.1 microns) is even better if you can find that, and you believe their claims are credible, and it meets my other criteria.  Smaller particles are harder to remove from the air, so just because a filter is really efficient with larger particles like dust or pollen doesn’t mean it will remove small particles well.  One filter that I was aware of prior to COVID that filters small particles well is the Filter Queen Defender.  A friend of mine did a lot of research and ended up buying this one, and it’s probably the one I would buy if I were in a situation where I needed one.  It’s not cheap, but they do come up for sale used on ebay sometimes.  

A good place to look for other room air filters is the AHAM (Association of Home Appliance Manufacturers) directory.  Anything showing up in this directory has been tested by them and has presumably been on the market for a while.  If you go to their directory and type in the size of your room it will give you a list of filters that will reduce airborne particle concentrations by at least 80%.  They rate filters based on how well they filter tobacco smoke, dust, and pollen.  Tobacco smoke is the smallest of these options so from the list of products it generates you want to select highest tobacco smoke CADR that you can afford and find.

Once you find a filter that you think you’d like to buy, you should check that it meets ozone limits.  Some devices that are sold as air cleaners can generate some ozone.  Ozone is a lung irritant, so presumably it’s not something that we’d want to be breathing during a lung-related pandemic. The state of California doesn’t allow ozone-generating devices to be sold there and they’ve been nice enough to publish their “good list” for the rest of us to use.  So head on over to the California Air Resources Board’s directory and make sure your room air filter is listed on their web site before you buy it.  

Make sure that you understand where to buy replacement filters, how often replacements are recommended, and how much they cost.  These can be a significant cost of ownership.  These may become harder to get if filters catch on as something a lot of people are buying, so picking up an extra now is not a bad idea.  

So, to recap:  

Step 1:  Go to the AHAM directory, type in your room size, and select a filter from the list with a high CADR.  

Step 2: Check and make sure that your selected filter is listed as California certified for ozone by CARB.

Step 3:  Price shop, consider resale options like ebay, and make sure you know where and when to buy replacement filters.  

Stay healthy, everyone!

Copyright 2020  Amy Musser.