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RHR: How to Reduce Viral Exposure When You’re Stuck Inside, with Michael Schrantz


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As fall and winter approach and as the COVID-19 pandemic continues, it’s likely that we’ll all be spending even more time inside of our homes—which could mean more viral exposure. In this episode of Revolution Health Radio, I talk with indoor air quality expert Michael Schrantz about the practical ways you can improve your air quality and reduce your viral exposure even when you’re stuck inside.

Revolution Health Radio podcast, Chris Kresser

In this episode, we discuss:

  • How you can reduce viral exposure while you’re indoors
  • How to improve your home’s ventilation
  • The pros and cons of air purification and filtration
  • Practical steps to improve your indoor air quality

Show notes:

Hey, everybody, Chris Kresser here. Welcome to another episode of Revolution Health Radio. Eighteen months now into COVID[-19], it’s clear that ventilation and air filtration are two of the best strategies for preventing transmission and infection.

In fact, a few months into the pandemic, I shared a simple formula for assessing the risk of becoming infected, which is the volume of viral particles times the length of exposure equals the amount of risk. In an indoor environment, the volume of particles and length of exposure tend to be higher. So if you’re in an enclosed space with no ventilation and there are several people who are infected, then there are going to be a lot of viral particles in the air. People tend to spend significant periods of time in rooms, whether they’re working or at home, or what have you. So that’s one reason why the risk of infection indoors is so much higher. Data from a study that was published in the Lancet in September 2020 show that [in] indoor air without filtration, it can take weeks for aerosol viral particles to fall five feet to the ground. This means that if someone visits your house and they have a high viral load and cough or sneeze, those particles may stay airborne for a really long time. So both ventilation and air filtration affect the volume of particles you’re exposed to and the length of exposure.

Ventilation means that the particles are going to move out of your range of exposure more quickly, typically. So this is, of course, why being outdoors is so much safer than being indoors during the COVID[-19] pandemic. It’s also why there have been so few cases and outbreaks associated with air travel. Airplanes now have very effective air filtration. This is why the [Centers for Disease Control and Prevention], the [Environmental Protection Agency], and many other federal and international agencies recommend ventilation and air purification as strategies for protecting against infection. Unfortunately, most buildings in the [United States], whether they are homes or businesses, have poor ventilation and weak or even non-existent filtration. You can open the windows in your house, of course, but that isn’t very practical if you live [in] let’s say Chicago in the winter, or many climates, in fact, and winter is the season when COVID[-19] is most likely to be surging.

Last year, right around this time, I recorded a podcast episode with Mike Schrantz, who is an indoor environmental professional and an expert in these topics. We discussed the ins and outs of ventilation and air filtration, particularly in the home. So given that we’re approaching winter again here in the Northern Hemisphere and we’re still dealing with COVID[-19], I decided to rerelease this episode so that folks who didn’t get a chance to hear it, or maybe even those [who] did, can hear it again because ventilation and filtration are as important as they’ve ever been, maybe even more so. And this information is still highly relevant. In the episode, Mike and I didn’t recommend any specific air filters, but I’ve gotten a lot of questions from you folks as listeners and also people on my email list and social media channels about which air filter I recommend because there are a lot of options on the market. I think there’s a lot of confusion, as well, about what makes a good air filter and which ones are the best options.

After the interview with Mike, I share my top pick for an air filter that you can buy for your home or workplace or any other indoor environment that you’re spending a significant amount of time in. So make sure to catch that if you’re interested at the end of the episode. All right, so let’s dive into this interview from last year with Mike Schrantz.

Mike is the founder and operator of Environmental Analytics. He has over 20 years of experience in improving indoor air quality and building science. And [in] the first podcast that I did with Mike, we talked about indoor air quality in the context of mold and other biotoxins that you might encounter from water damage. That’s a big issue that’s, of course, been around for, really, as long as we’ve had buildings, but [there has] certainly [been] an uptick in mold biotoxin-related illness in the past couple of decades. In this show, I wanted to talk with Mike about changes that we might be able to make to our home to reduce our exposure to viral load during the COVID-19 pandemic.

And throughout the pandemic, I’ve talked about the risk of infection being a product of the volume of viral exposure, multiplied by time, so anything we can do to reduce that volume of viral exposure is a good thing. And [most of us are] going to be spending a lot more time inside as the fall and winter months approach. So I thought it would be helpful to talk about some things we can do to reduce that viral load exposure during the season to come. So, without further delay, I give you Mike Schrantz.

Chris Kresser:  Mike, [it’s a] pleasure to have you back on the show.

Michael Schrantz:  Chris, thanks for having me.

How You Can Reduce Viral Exposure While You’re Indoors

Chris Kresser:  So I’m just going to jump right in here. COVID[-19] is on everybody’s mind, of course, and we are heading into the fall-winter season where, in most places, I know in Tucson, Arizona, this may not be true, but it starts to get cold. And flu season is approaching, people are worried about a spike in COVID[-19] infections, [and] people are going to be spending a lot more time indoors. And all through this pandemic, I’ve been saying that the risk of infection is a product of [the] volume of exposure to viral particles multiplied by time.

So I want to talk to you about how we can reduce the volume of exposure to viral particles in our homes, and perhaps in other indoor environments. If someone’s a small business owner or rents an office somewhere or has some control over that indoor environment, how can we approach this indoor air quality issue so that we can create the healthiest living spaces that we can through this winter and beyond, for that matter?

Michael Schrantz:  Yeah, absolutely. We know that mechanical ventilation or even natural ventilation is a big topic. We can dive into that one, obviously, deeper. Filtration is going to be another successful way. And there’s a little bit of stuff coming out about purification, which I’m happy to elaborate a little bit more on in terms of the differences between [the two]. You hear terms that are interchangeable to certain people. Purification isn’t that filtration we’ll technically know, or if we’re filtering something out, we’re removing it; we’re filtering it. If we’re purifying it, we’re adding some sort of technology. But yeah, I think there’s a lot of potential improvements. The top two to me are going to definitely be filtration and some form of ventilation, which, as you indicated in the beginning, it might be good for somebody like myself in Tucson, Arizona, where we can just open up a front window, and a back sliding glass door. But that doesn’t do much for people in the colder climates.

Chris Kresser:  Right. Yeah, let’s talk a little bit about ventilation. I wrote an email a few weeks ago and did an Instagram video about the importance of ventilation. And this turns out to be one of the biggest factors influencing the risk of acquiring COVID[-19]. And of course, this is why outdoor activity has been one of the main recommendations throughout the summer months because that’s a very well-ventilated environment. That’s the best kind of ventilation you’re going to get. So even if you’re standing relatively close to someone, and they’re infected, and they’re talking or even singing or shouting, the viral particles that are emitted will disperse fairly quickly and become diffused in that outside air.

And it’s interesting to me how in the mainstream media, there’s not actually a lot of discussion about ventilation in indoor environments and that as a potential[ly] modifiable risk factor. I’ve seen it in some stories about airplanes and how air travel has been surprisingly safe until you understand how well purified the areas and how ventilated the air is in an airplane. There’s [a] change of air every two, three minutes in most airplanes. So yeah, what are the key factors for ventilation? Maybe starting with how does someone even know whether their house has good or poor ventilation?

Are you concerned about the health impact of staying indoors during the pandemic? Check out this episode of RHR for tips on improving your home’s indoor air quality and reducing your viral exposure. #optimalhealth #wellness #chriskresser

How to Improve Your Home’s Ventilation

Michael Schrantz:  [Use] an air conditioning company or somebody who is certified to do what’s called blower door testing. There’s an organization and there’s a couple of them out there. But Building Performance Institute is an example of an organization that can come out to your home and do pressure testing. We don’t know how leaky or tight your home is. And there are rules of thumb. If the house is built prior to the energy crisis on the edge of the late ‘60s and early ]70s, you might be what’s classically defined as having a leakier home, and the opposite is true as you get into the more recent times where houses are being built extremely tight, which means they’re not getting a lot of natural ventilation. Stuff that’s coming through the cracks, the crevices, and that sort of thing. So numerically, if you don’t know where you’re at and you’re trying to get an idea of [whether your] house [is] poorly ventilated, it starts with working with a professional company [that] can come out and do that type of testing or else it is kind of just guesswork.

Chris Kresser:  Right. So you said, general rule of thumb, more recent houses actually have poorer ventilation, which is interesting. Because I mean, that is good from an energy efficiency standpoint, right? So you’re going to have less heat escaping, or air conditioning escaping. And it’ll be better from an energy efficiency standpoint, which is why the newer houses are better sealed. But there was a kind of unintended consequence there with those better-sealed houses.

Michael Schrantz:  And never has that been more true than on the topic we’re dealing with today. It is an inverse relationship holistically. The energy crisis led the way. Tighter homes, lower utility bills, all of that good stuff is certainly attractive. But it comes at a consequence, and usually with indoor air quality, and I won’t go eight levels deep here, but there were chronic exposures. People were starting to feel weird, feel bad, sick building syndrome, you name it. Newer homes are going to be …

Chris Kresser:  Mold, [volatile organic compounds] (VOCs), all that stuff. Right?

Michael Schrantz:  Right. Exactly.

Chris Kresser:  Yeah.

Michael Schrantz:  So testing is the first step.

Chris Kresser:  Yeah, we just had one of these tests [done by a] local company in Utah. And a lot of times, these energy efficiency companies, where their business is to do upgrades for improved energy efficiency, will do a blower door test for free as a way of helping you to kind of assess what needs to be done. And sometimes local utilities will do them, as well. Our local utility offers credits if you have a leaky house. Here we’ve talked about leaky gut on this show, leaky brain, leaky skin, leaky lung, now we’re talking about [a] leaky house. If you have a leaky house, putting some money toward those upgrades sometimes can get you an energy credit. But you have to balance that, as we’ve discussed, Mike, where in our case, our house is probably so leaky that even if we do some sealing, we still are not going to be in that tight house where it becomes a health threat area. So it’s kind of where a homeowner has to assess what their goals are, and then where they’re starting from and where they want to get to.

Michael Schrantz:  To go along with what you’re saying, one of the issues I ran across in the research. Take, for example, the airplane example of ventilation. And I’m familiar with that. What a lot of people don’t know [who] are listening is that that’s primarily based [on] occupancy. So when you slam 150 people in a 737 aircraft, in a relatively small vessel, they’re compensating to improve the indoor air quality by changing the amount of fresh air that comes on. And that’s why, when you look at other things like commercial buildings [and] schools, you’re going to see higher guidelines for ventilation, air changes per hour, or ACH is the term. But when you look at residences, you’ll notice that the requirements all of a sudden fall off, and all of a sudden now it’s, like, 0.35 to maybe on the upper end, as just an example, one air change per hour. And people are getting all the data mixed up, because they’re like, “Well, can I just make my house six air changes per hour?

Chris Kresser:  Right. Two to three changes per hour. Yeah.

Michael Schrantz:  And you can’t do that.

Chris Kresser:  You need to live in a clean room. Yeah, yeah, if you [have] a 2,000 square foot house and a family of four, that’s a fundamentally different concentration of people per square foot than in an airplane, right?

Michael Schrantz:  Exactly.

Chris Kresser:  That’s fairly obvious. And obviously, less carbon dioxide and other stuff being emitted. So all right, so let’s say someone does a blower door test, and they find that their house is very tight. Maybe they have a newer house, [and] they have poor ventilation. What are some of the options then? And we can do this by climate. So let’s say, as you said, if they’re in a warm climate, the easiest low-tech but effective option is just opening some windows, right?

Michael Schrantz:  Yeah. And I would argue, obviously, it’s preferred. Excluding the wildfire scenario, or poor outdoors, that whole thing, that whole disclaimer put to the side, the amount of air changes you can get on a nice day through your home is going to arguably be more than the realistic mechanical ventilation. So just to clarify.

Chris Kresser:  Wow, especially, yeah, if you have a cross-breeze. Yeah, so maybe if you live in an apartment in Shanghai, you probably shouldn’t open your window, right?

Michael Schrantz:  Right.

Chris Kresser:  But if you’re in a place with relatively good air quality, that’s the number one. And yeah, maybe people will be willing to do that even when it’s pretty cool outside as a trade-off from the potential of having a home where the ventilation is poor and viral particles might be higher, versus putting on a sweater and having the heat on maybe a little bit less. I don’t know. All right, so then if someone lives, let’s say [in a] very, in Minnesota, or Chicago, and opening a window is just not even feasible [during the winter], what are the options there?

Michael Schrantz:  If we’re talking about, of course, I’m anxious to tell you about other alternatives. But on the topic of mechanical or ventilation in general, you’re going to be looking at probably mechanical ventilation. Mechanical ventilation is when you have a dedicated device that is bringing in outdoor air, hopefully filtering it to some level of minimum efficiency. You’ll see it’s not uncommon for some nicer units to have a MERV 11 or MERV 13 filter.

Chris Kresser:  Right.

Michael Schrantz:  And then ultimately injecting that fresh filtered, and if you’re running it through an energy recovery ventilator or a heating recovery ventilator, depending on your climate, you’ll be transferring energy from the air. So in plain English, if you have cold outdoor air, this device is designed to also exhaust out warmer air from the inside, thus warming in the incoming air. Here’s the challenge. You can’t just go out to your local air conditioning supply house and buy. Because most people are of the thought of if a little is good, more is better. And you can buy some oversized mechanical ventilation device that dumps in too much air. Because if you’re heating, we’re using the winter as [an] example.

Chris Kresser:  Right.

Michael Schrantz:  If your heater can’t keep up with that load, all of a sudden, you’re going to run into a couple of issues, one of which is comfort. It’ll be freezing cold in the house. And by golly, you got that monster unit. So I try not to over plug this disclaimer, but every time you talk about installing a device, everyone needs to assume that they need to bring in a professional who understands [guidelines from] ASHRAE, which is an organization that establishes ventilation guidelines for residential and commercial sectors, and have them look to see what is the maximum amount, what’s the appropriate amount of mechanical ventilation that your particular home can receive?

Chris Kresser:  Right, right. All right, so, or you just poke a few holes in your wall.

Michael Schrantz:  Sounds like natural ventilation again.

Chris Kresser:  Pull out your weatherstripping under the doors and windows and pretend you have an older house. So that’s, ventilation is key. And there are various options for dealing with it, as we just mentioned. And those are going to vary depending on your climate, when your house was built, [and] what your current status is as assessed by the blower door test. Let’s talk a little bit, or anything else to say about ventilation before we move on to purification? Because I think there [are] quite a few options that we should cover.

Michael Schrantz:  Yeah, I think with mechanical ventilation, it just boils down to understanding that [and] not getting caught up in [it]. Listen, we’d love for your house to be a cleanroom where you have a laminar flow of air coming through because that would be the ultimate dilution technique. But that’s not realistic. Your goal is going to be working in concert with a bunch of other things. This is just one component. You get the optimal amount of either natural ventilation or mechanical ventilation your home can take and then you do other things, which we’re about to talk about.

The Pros and Cons of Air Purification and Filtration

Chris Kresser:  Great. All right, so let’s move into this. And again, the context here is we’re trying to reduce the viral load exposure. So why are we talking about this? Well, let’s say a scenario where you have to have a repair person come to your house. You have no idea [if] they have COVID-19 and they’re in your house for a few hours. Well, ideally, you’d want to have some kind of mechanism for filtering and purifying that air so that your exposure to that viral load would be lower. Or let’s even say one of the family members gets infected. And in most cases, the family member [who’s] infected will be semi-isolated. Maybe they live in their bedroom for a little while to prevent infecting other people. But obviously, they’re still breathing, air’s circulating around the house, [and] their bedroom’s not completely hermetically sealed from the rest of the house. So this is another way of purifying the air or reducing that viral load exposure for anyone [who] happens to be in the house [who] might be infected, whether they know it or not.

So air purification and filtration. So let’s first talk about, you kind of briefly mentioned the difference between filtration and purification. But maybe you could give some commercial examples that are out there, like the difference between a filter and a purifier. And then which you would use in what situation. What are the pros and cons of each?

Michael Schrantz:  Sure. So filtration first, make no mistake about it until additional research comes out, it’ll probably be the safer go-to for those listening. And here’s why. Filtration is the physical removal of an airborne contaminant. And we’ve learned a lot; there is so much information online, you can only imagine. Well, I’m sure you can. In terms of the average size of the virus, depending on what you see is about a 10th of a micron. But then it comes out in respiratory droplets. So they may be bigger. And it’s all this stuff that leads into what is an appropriate filter that could, can you scrub the air physically to remove or lower the concentration so that people have a better chance of not getting infected?

And filtration is a proven technology. It’s been around for over a century. I’ll give you a couple of quick nuggets here. What you can find when you read, whether it’s from the [Centers for Disease Control and Prevention] (CDC), the [U.S. Environmental Protection Agency] (EPA), or both of those organizations that will reference ASHRAE, which again, can establish a lot of information including giving you information on filter efficiencies, they’ll recommend things like MERV filters that are somewhere in the neighborhood of 13 to 14. So this idea of having, you have an air conditioner, whether it’s an air handler, a furnace, and it can do heating and cooling, [and] you have a filter on that. And they’re recommended as guidelines to use a MERV 13 or higher. But there’s this huge caveat in big bold letters, that’s basically saying you need to make sure that your system can handle it.

If you slap a big filter that’s overly resistant in your system, because you think if MERV 14 is good, MERV 16 might be better, which you would be right in that sense, your system may not be able to handle the resistance. So filtration, a lot of times what we’re recommending for people who especially don’t have more robust systems, and one way for them to find out whether their system can handle higher MERVrated filters is, of course, going to an air conditioning company [that] knows how to measure that, is to bring in portable filtration devices. And I mean, I’m happy to give a couple of examples, but there is a commercial unit that I have in my son’s bedroom that provides hyper [high-efficiency particulate air] (HEPA) filtration. So much higher than MERV 16, and really able to scrub the air. And just to do some quick math with you, his room is getting about eight to 12 air changes per hour, filtered changes of air. To lower it is a great way, and is well documented and supported by the CDC and the EPA, to filter the air out, to lower those concentrations in combination with natural or mechanical ventilation when you can. There’s a couple of exceptions there. But that’s the primary thing.

Chris Kresser:  Yeah, people are, as you know, there’s a lot of marketing hype out there with filters and purifiers. And I think it’s really difficult for the average buyer to be able to sift through that and really know what’s legit and what’s not.

Michael Schrantz:  Fair enough. What you’re going to get for these higher-end models is a higher sense of confidence that they’re going to filter out particles at the marketed or advertised specifications because they have the science, [and] they have the money to have done that.

Chris Kresser:  Independent third-party verification.

Michael Schrantz:  Exactly. That’s key because everyone, they’re hiding behind words like HEPA-like or HEPA-type and you’re paying what you think is good money for true HEPA, but you’re not getting it. Those are two examples that work really well. And I’ll tell you, I had a particle counter in my son’s room when I first installed it. And again, this is not exactly a laboratory setting, but take a room that’s 10 [feet] by 14 feet in dimensions, eight and a half foot ceilings. In less than 20 minutes, I was able to get that 0.3 micron size particle 24 percent of the outdoors as a comparison, which is extremely good.

HEPA is going to offer you better filtration, much better filtration than a MERV 16. However, MERV 16 is pretty good, too. And a quick piece of information that’s useful. If you look at a graph of a filter, and how it’s able to remove, its efficiency or performance out of any particular particle size. Typically, the particle sizes that we’re looking at, you hear people saying, “Oh, it’s 99.9 percent efficient at 0.3 microns.” Whether you have a MERV 16 or a MERV 14, the size of the virus, and even some of the suspected particle sizes that [the] virus might be attached to, is going to have better filtration than the 0.3 rating. So, in other words, you’re actually getting a little bit better filtration than you think you do for any given filter. But most people, Chris, don’t have the access or the ability to run a MERV 16. In your case, that Perfect 16 is a great option, because you had the physical room to install what was a large box of banks of filters to get it down to that rating.

Chris Kresser:  Right. And the advantage also to the portable filters, you can, so you just mentioned that got it down to [24] percent of the outdoor value in 20 minutes. So in theory, you could have the filter in the kitchen during the day or [in] the living room or a home office or living space like that, and then take that up a half-hour before your kid goes to bed and put it in there, right?

Michael Schrantz:  Yeah, all other things being constant, one of which is doors and windows shut, you can’t filter the air. If your doors and windows [are] open, you’re not going to get that type of differential. And of course, the leakier home is going to be harder to filter out and get those lower numbers than a tighter home. But yes, in general obviously, because another part of this topic is okay, fine. So what the audience is hearing is that whole house filtration is definitely something to look at, work with your air conditioning company to make sure that you’re not over-installing something that’s too resistant. But portable filtration devices are a quick, easy way to get superior filtration. The next question that always comes up is how many? Because you’ve seen this, right? Online, it’s like this unit [is] good for up to 1,500 square feet.

Chris Kresser:  Right.

Michael Schrantz:  Based [on] what metric? Somebody with COVID[-19]? It’s based [on] perfect mixing.

Chris Kresser:  Are the doors open, [or] are they closed?

Michael Schrantz:  That’s right.

Chris Kresser:  How sealed is the house, etc.?

Michael Schrantz:  There’s a rule of thumb that I finally was able to find that comes from ultimately, infection and control and all that. And it’s a crude number, but it’s a good one. And the argument was for the area that you’re trying to filter, if you can get greater than or equal to 12 air filter changes per hour, that’s kind of a good, keep it clean, environment. So if you think about that, I did some quick math before we got on. And if you take an average room, 10 [feet] by 10 [feet] with eight and a half foot ceilings, and you say okay, that’s 850 cubic feet. And then you say times 12 because that’s how many air changes you’d want to have in an hour. And you do the arithmetic of how many cubic feet per minute do I need to filter to get 12, the number would come out to 170. Again, that assumes perfect mixing, which there’s not, but here [are] the ideas. Most of these higher-end or even medium-level portable filtration units will get you 170 cubic feet per minute in that scenario. So these are very attainable options for people to get superior filtration.

Chris Kresser:  Cool, that’s helpful because that is a big question that comes up a lot. Okay, so there’s a whole bunch of other options now that fall into the category of air purification. And so there are ozone-based units, ultraviolet (UV), a bunch of other technologies that are coming on the market. Some companies now are combining purification with filtration in the same unit. So what’s your take on purification? Does that have any additional benefit above and beyond filtration if you have a great unit? Should you even consider purification? Is there any situation where you would consider purification in lieu of filtration? Let’s break that all down.

Michael Schrantz:  Yeah, no, and it’s a good question. Here’s the thing with purification. I’m reminded of some of the concerns I’ve always had about purification, pre-COVID[-19]. There [were] always general concerns about byproducts or what’s called technically intermediates that can be created. Basically, the incomplete destruction of a particular contaminant in the air with these purification devices like UV light [and] ozone. You’ve heard [of], many of you have hydroxyl radicals. There’s nothing that I was able to find, Chris, that shows number one, superior performance to break down COVID[-19], or at least the virus that creates COVID[-19], in a reasonable time, or in a reasonable environment. And here’s what I mean. You have some companies that are working with different commercial airlines, where they will push a UV system, an empty plane, through the aisle of a plane, and have high doses of UVC to kill. And based [on] the intensity, and time that you’re saturating a given surface with, there [have] been studies that would show that that’s effective at killing.

But that doesn’t really help you out in a residential home for a couple of reasons. First of all, you’re not going to buy the device to do that. Second of all, there [are] exposure concerns. Ozone is, at minimum, a respiratory concern at levels that can actually kill. Same with UV light. There is a newer technology that they’re looking at. There [are] two forms of UV light. That’s where it seems a lot of attention right now with purification is going. One UVC option [is] ceiling-mounted, or high wall-mounted devices that shine the UV toward the ceiling. But you’re seeing this more in commercial applications, not necessarily residential homes. You can imagine walking into your friend’s house and there [are] these random lights that are shining upward. There’s an issue of how much dwell time the virus need[s] to be exposed to that virus. The bottom line is [that] it’s not well-known yet.

There’s a UVC stream called far UVC, which is the 222 nanometers of emission or wavelength. They’re looking at that right now, Chris, this idea that you could turn this device on in your home or in restaurants and be exposed to it and because of the wavelength, there’s under a certain, as long as it meets other parameters, it’s not going to be an exposure concern. But all of this stuff is [the] tip of the spear. There hasn’t been decades’ worth of consensus that purification would work. I think what it boils down to is qualitatively, okay? Qualitatively we understand that purification techniques can work, but you’re asking about quantitatively. I know this thing can kill a virus, [but] how much of it can it kill? If the average sneeze or cough throws out anywhere from 500 to 20,000 virions of this virus, how well of a job is it going to do?

So what I would invite the listeners to consider is user beware. Do your research. Look up the technologies. See what sort of independent third-party studies that they have are showing to report [the] performance of these units. And what are the possible side effects? The EPA has a document, right along the same document or page that you’d find online for their recommendations, I should say, the EPA for residential homes, and it gets you a link right to that paper. And they’re concerned about what they don’t know about the technology before they have a bunch of people go out and start buying it.

Chris Kresser:  Yeah, I mean, it sounds like there are a number of technologies [that] may be promising. But the data aren’t quite there yet. And there are some concerns. So it seems to me that if there’s certainly no additional proven benefit of purification beyond filtration, then it doesn’t seem to make sense to mess with that too much at this point.

Michael Schrantz:  Well, and I think to me, Chris, the truth is it’s the unknown risk. Because I would argue that in favor of UV light if it was an unoccupied building. And therein lies the point, we’re not talking about what we do with our homes when we’re not living in them. We’re talking about being exposed to them. And the other part of it, too, is because people thought, well, we’ve heard about adding UV light in the ductwork. And again, there are applications where putting a UV light by the evaporator coil in a humid climate could be a great way to minimize microbial growth. We’re not talking about microbial growth right now. But that would be a great way to minimize that under certain conditions and considerations. But if you think about dwell time, dwell time is the amount of time predicted [that’s needed] to kill the virus or damage it so that it can’t replicate in your body. That’s the important part here. It’s not short seconds; it’s typically minutes.

And when you have a virion, on a particle that has the virus in it, that’s flying through the ductwork at somewhere between 400 and 700 feet per minute, if you do the math in your head, it’s not getting minutes of exposure; it might get a second depending on where the bulb is. So this is what I mean is I’d like to talk about it more like if you were a family member, what would be the great ways to improve the overall indoor air quality of the home and beyond following, by far, the CDC, EPA, [and the] World Health Organization, which are all pretty much in line with washing your hands and [using] proper [personal protective equipment] (PPE), it would be filtration, and mechanical or natural ventilation. Those would be the top items.

Chris Kresser:  Great. So [I] just want to say something that maybe goes without saying, but [I] want to kind of highlight it because we didn’t mention this too much in the beginning. All this stuff that we’re talking about [is] not just going to be helpful for COVID[-19] protection, [but it is] going to also be helpful for just improving indoor air quality overall, and improving health overall. Because we know from so much research now that improving indoor air quality is one of the most important things we can do to improve our health and protect against diseases. But it’s one of the last things that I think people tend to think about. So this is an opportunity, and maybe a greater source of motivation with this acute COVID[-19] crisis. But any steps that you take to improve your indoor air quality will be valuable well beyond the lifetime of the COVID[-19] pandemic.

Michael Schrantz:  Absolutely. This conversation and, ironically, a lot of the staple solutions that we’re talking about today stem from other sorts of contaminants and exposures that we’ve been dealing with for decades. We know that they work, [and] we know that they present minimal exposure issues. And the other part, and this comes up a lot, is it’s like you said, whether it’s a temperature issue, or it’s an issue of wildfires. I’ve heard there [are] a few going on right now in California as an example.

Chris Kresser:  Oh boy, yeah.

Practical Steps to Improve Your Indoor Air Quality

Michael Schrantz:  Mechanical ventilation or natural ventilation may not be an option, right? I mean, you might notice an adverse condition by leaving that window open one day. That’s why you need to arm yourself with all these other things so that they can work in concert with each other, this idea of added filtration, portable devices. I think, somewhere between 150 and greater, that [is]going to be in a price range you can afford and stick one in your bedroom, stick one in your living room, and know that okay, on a day that I’m going to just open up my doors and my windows and get ample outdoor air. By the way, I’m looking forward to that in Tucson. I’m not going to run that filtration device and waste its energy and time because I’m just filtering the world. But I know that when I close my house up, now I have the ability to turn this filtration unit on. And that along with good clean habits, washing my hands, trying not to be up in front of everybody’s face who visits my house, all those sorts of things are the low hanging fruit options of minimizing exposure in the long run.

Chris Kresser:  Yeah, and don’t let the perfect be the enemy of the good is what you’re saying here.

Michael Schrantz:  Exactly.

Chris Kresser:  There’s the sort of superior premier models, but then there are other models that are also way better than not having any filtration at all.

Michael Schrantz:  Exactly.

Chris Kresser:  Are there any rating sites or organizations? You mentioned a few organizations that are more related to ventilation, but any kind of places that rank air filters, or what standard should people be looking for? Is there kind of a minimum MERV value that you want to see below which it doesn’t make sense to use that device?

Michael Schrantz:  Golly, any filtration is going to be better than no filtration assuming it’s still a good working filter. Even a MERV eight filter or MERV six that offers relatively poor performance, it doesn’t mean it doesn’t offer any. What I would recommend for people who are looking at air filtration that deals with their air conditioning systems, so we’re talking whole house filtration, is to work with your local air conditioning company to find a way to install a MERV 13 or higher based [on] what is coming out of the ASHRAE recommendations and suggestions based [on] the curves on what they’re able to remove at these given particle sizes. MERV 14 seems to be the ideal target. But don’t sweat it if your unit can handle it. If you’re in a very financial[ly] tough spot, or there’s not the physical room to install these types of upgrades, you also have portable filtration, which we spent some time talking about. That is a great option. In fact, in some cases, it might be the preferred option over marginally improving what may be a MERV six filter right now on your system to a MERV eight.

This information is coming from independent studies from filtration studies. The EPA and the CDC are smart not to specify things because they’re afraid people will abuse it, [and] not understand that it’s complicated. You can’t just slap in a nice filter. But I think if you could do a combination of what we’ve been talking about today, you’re going to be eons better than the majority of people [who] are in less fortunate situations.

Chris Kresser:  Yeah, so we had a previous podcast where we talked a lot more about filtration and indoor air quality in the context of mold and other biotoxins that you might encounter in the indoor environment. So for folks [who] are interested in that, just Google “Kresser Mike Schrantz Revolution Health Radio,” and that should pop right up. Or we’ll put the link in the show notes, as well, [and] you can check [it] out on the website.

And, Mike, thanks again, for coming back on the show. I think this is a really interesting way that we can reduce our exposure, reduce our risk over these winter months, especially when we’re going to be spending more time indoors. It’s probably not on a lot of people’s radar. So I always appreciate your expertise in these areas.

Michael Schrantz:  Thank you very much, Chris. I appreciate the opportunity.

Chris Kresser:  All right, everybody. Thanks for listening. Send in your questions to ChrisKresser.com/podcastquestion and stay healthy and well this winter.

Okay, now that we’ve covered the basics [of] why improving the quality of indoor air is so important, I want to tell you which air filter I use myself and recommend to my patients, the doctors and coaches I train, and my friends and family. But before I do that, I want to cover some of the most important variables to consider when you’re choosing an air filter. The first is the number of air changes per hour. I talked about this with Mike in the podcast, but experts recommend cleaning the air five times per hour or one air change every 12 minutes for maximum effectiveness. Again, as a side note, airplanes do even better with a change every two to three minutes. And I think that explains why air travel hasn’t been associated with significant outbreaks, despite people sitting close together for long periods. So that’s how important the number of changes of air per hour can be. How often an air purifier can clean the air is a function of how much air it moves and the size of the space it’s in. You really need to pay attention to this because some air purifiers or manufacturers of air filters and purifiers claim that their products can change the air five times an hour. But when you look at the fine print, you see that that’s only true in like [a] 100 square foot space. Or some companies might claim that their filter can clean a 2500 square foot area, but at that size of a room, it will only be one change of air in an hour, which isn’t enough.

The second factor is a little easier to understand, and that’s just how effective the purifier is at removing potentially harmful particles from the air. This can include things like particulate matter you would find in air pollution, mold, bacteria, and, of course, viruses. And some of these particles, like viruses, can be really, really small. So it’s crucial that the purifier can remove those, as well. The third factor is whether the purifier also captures toxic volatile organic compounds or VOCs. A lot of the cheaper [high-efficiency particulate air] (HEPA) filters don’t do this, but I think it’s crucial because these compounds can cause serious issues for some people. The fourth factor is noise. Some air filters are really loud; it sounds like an airplane [is] taking off or something. And I’m particularly noise-sensitive. So having one that operates quietly is essential for me.

The fifth factor is cost and, in particular, cost relative to effectiveness, because even the cheapest air filter, if you pay 75 bucks, if it doesn’t work, that’s a wasted $75. So we can’t just look at price; we have to look at cost-effectiveness. And this can be measured with air filters with the metric cost per clean air delivery rate (CADR). CADR is a metric used to measure the effectiveness of air filters. So if we take cost as a function of CADR, that can give us some more insight into just how cost-effective an air filter is.

With all that in mind, my pick is the AirDoctor group of filters. So let’s see how they stack up against my criteria. Their most popular product is the AirDoctor 3000, [which] cleans the air once every 12 minutes or five times per hour in a 500 square foot room. They also have a product for smaller spaces, the AirDoctor 1000, which cleans the air five times an hour in a 235 square foot room. And then for larger spaces like a living room or a great room, the AirDoctor 5000 cleans the air five times an hour in [an] approximately 870 square foot room. In terms of effectiveness, it’s tough to beat the AirDoctor. It filters 100 percent of airborne particles as small as .003 microns in size, and that makes it 100 times more effective than typical HEPA filters. And in an independent third-party lab test, the AirDoctor remove[d] 99.99 percent of a test group of 11 bacteria and viruses, and it’s obviously very important in the world that we live in today especially. As far as gases like volatile organic compounds (VOCs), AirDoctor’s dual-action carbon gas trap, VOC filter captures toxic VOCs. These could be VOCs from off-gassing furniture, building materials, paint, carpet, household cleaning products, and even formaldehyde and ozone.

AirDoctors are super quiet. I’ve used a lot of air filters and purifiers over the years, and I find that the AirDoctor is the least obtrusive that I have used. It’s not just that they’re 30 percent quieter than standard HEPA filters, which they are, but it’s the pitch or the quality of the noise, I think, that makes an even bigger difference. Some of the other air filters, like I said, kind of rattle around and sound like a plane is taking off or they have this really high-pitched whine that drives me nuts. But the AirDoctor is almost like white noise. It just fades into the background really easily. Finally, AirDoctors are extremely cost-effective. I think they’re probably the most cost-effective filter on the market. Some other filters have a cost per CADR ranging from $5 to $8. For the AirDoctor 3000, which is their most popular unit, it’s about $1.50. That is between three and five times more cost-effective than other filters that people tend to buy. So it’s clearly a much better deal, and it’s even lower if you take advantage of the discount I’m about to mention.

I’ve worked out a special group buying discount for my community through AirDoctor. You can save up to $300 off the retail price, which is nearly half off of the AirDoctor 3000. They also offer payment plans with a company called Affirm that [has] payments as low as $30 a month, which can be a good option for some people. To learn more about these filters and take advantage of this offer, go to kresser.co/airdoctor. I have a few filters in different rooms in my house. I love how fresh and clean the air smells, and I love the peace of mind that they give me. As many of you know, we lived in a house with serious mold issues many years ago, and it caused really significant harm to my family’s health, to all three of us. And since then, I’ve been very serious about maintaining indoor air quality. And of course, in the world that we live in today, I’m happy to know I have air filters that capture 99.99 percent of the bacterial and viral particles that were tested. And that’s especially true as we’re moving into the winter and I’ll be spending more time indoors. So again, go to kresser.co/airdoctor to check [out] these [air filters] and pick one up. I hope this was helpful and leads to cleaner air for you and your family.

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