Home Cleaning Tips My Interview With Indoor Air Quality Extraordinaire, Author, and Scientist Jeff May

My Interview With Indoor Air Quality Extraordinaire, Author, and Scientist Jeff May

by Catherine

How to Know If Your House is Killing You With Jeff May

When you are looking for someone to trust on all matters concerning indoor air quality, hidden leaks, mold problems, weird or unpleasant odors, contaminated mechanical systems, and the overall “health” of your home, Jeff May should be at the top of your list. I know he is at the top of mine. As a matter of fact, I learned about Jeff and became acquainted with his expertise in the Indoor Air Quality (IAQ) and home inspections fields when my family was going through our mold nightmare. At the time, I was desperate to find information on how to fix our home, and found one of Jeff’s popular books, My House is Killing Me! The Home Guide for Families with Allergies and Asthma, at our local public library. It was the most comprehensive and helpful guide on the myriad things that can cause a home to get “sick” I had ever seen. Needless to say, I couldn’t put it down and later ordered his book, The Mold Survival Guide: For Your Home and for Your Health on Amazon—I can’t recommend it enough to others navigating the confusing world of mold in their home or anyone suspecting that something in their home is making them sick. To this day, I find myself referencing sections of the book when I am working on articles about below-grade spaces, like basements or crawlspaces, or wanting to understand more about proper attic ventilation or ice damming and mold growth. If it has anything to do with mold in a home, believe me, that book covers it!

The thing about Jeff May’s expertise is that it comes from boots-on-the-ground experience paired with a science background and a very personal understanding of what it is like to deal with allergies, and environmental/chemical sensitivities. Not only is Jeff a published author (his other books include My Office is Killing Me! The Sick Building Survival Guide and Jeff May’s Healthy Home Tips), organic chemist, certified indoor air quality inspector, home and building inspector, and certified mold and microbial inspector, but he is also a former adjunct professor at U. Mass Lowell and Chair of the Science Department at The Cambridge School of Weston. He even has a certification in Food Science and Technology.

Jeff has inspected and investigated thousands of homes as well as many buildings and schools. He sometimes even carries his own microscope to jobs for on-the-scene specimen identification—with his BA in chemistry from Columbia College and his MA in organic chemistry from Harvard University, he is uniquely qualified to do so. Jeff also deals with allergies and chemical sensitivities himself, so he has a unique understanding of the importance of his work and the health repercussions of bad indoor air quality. Jeff May is “the guy” who the other professionals call when they can’t figure something out, or need someone to teach them about mold and indoor air quality. In fact, Jeff was inducted into the Indoor Air Quality Hall of Fame in 2018 by the National Indoor Air Quality Association.

Recently, I was offered the opportunity to speak with Jeff about his work and his experiences investigating homes and, as you can imagine, I jumped at the chance. I was so excited to pick his brain and to ask him “all of the things” about indoor air quality and about maintaining a mold-free home that I could barely contain myself. It was difficult to trim down my litany of questions into a list that would fit into one blog post, but I did my best. I tried to keep myself limited to some of the most frequently asked questions about home inspections and mold from you, my readers. I am secretly hoping that our talk will be the first in a series, where Jeff would be willing to answer some questions more specific to singular topics later on—fingers crossed. I can always, hope, right? So, without further ado, what follows in my in-depth conversation with Jeff May of May Indoor Air Investigations LLC. Enjoy!

(Note: Since our interview is LONG and very detailed, I have divided it up by topic, so that you can skip around to what interests you most. If you have time, though, read it ALL. It is sooo good. Jeff is FULL of helpful information, especially for cleaning away mold that I had never heard before. Also, all photographs below were taken by Jeff May onsite at various jobs and inspections and are used with his permission.)

Professional Background, Experience, and Becoming an Indoor Air Quality Professional

Me: For the benefit of my readers who don’t “know” you and your background, like I do, I thought we could start from the beginning with you telling us a little bit about what you do, and what brought you to the field of building and indoor air quality consulting in the first place.

Jeff May:Sure. I actually started in life as a teacher, and then did some property development and ended up learning a lot about houses. My wife was a real estate agent for a while, and I didn’t want to continue doing the development part of things, so she said, “Why don’t you become a home inspector?” And I’d actually never heard of the profession before. So, I followed a home inspector around and fell in love with the work. I took classes and got certified and licensed. During that time, I looked at probably over a thousand houses. Sometimes I would feel sick in places, and often, I had to wear a mask. So, I started to make the connection between indoor environmental conditions, and how I was feeling. We also have a son with asthma, and he was quite symptomatic at home. We discovered that we had a huge dust mite problem in the beds, and when we put dust-mite encasings on the mattresses and bed pillows, everybody got better. Connections like that pretty much got me into the IAQ field. Also, as I was doing home inspections, I started taking some samples to look deeper into what was going on. I then took a class on indoor air quality in the Harvard Extension School from John Spengler, who’s a very well-known person in the field. So that really got me started. I liked knowing that I could look for problems, understand homes, and then make changes that could make people healthier.

Me: Well, that’s awesome. So, when did you transition from being more of a general inspector to an inspector for indoor air quality?

Jeff May: Actually, I started doing the home inspections in 1988. Then, about four or five years later, I took that air quality course. So very slowly over the years, I just did more and more air quality work. I think it was around 2004 when I actually sold the home inspection business and just did only air quality investigations. I’ve looked at thousands of homes now and helped many, many people.

Me: I love it! You truly happened upon your calling. So, when you go to a home these days, do you have a time where you call and speak to the homeowner before you are physically onsite? What I want to know is how much do you want to know about the problem before you arrive? Do you want to dig and ask them over the phone the things that they think are causing the problem, or do you like to just go in and investigate for yourself?

Jeff May: Well, Connie, my wife, does most of the initial contacts with people, although for the physician referrals, I usually talk to the people directly. But we always want to find out the conditions in the house: how old the house is, if the basement is finished or not, if there are carpets, what kind of heating and cooling is there? We have a list of things. And, we have two levels of service. One is an investigation, which is a really thorough look at the house. We look at every room in the house. The other is just what we call a consultation. That’s usually for just a particular problem. It might be a mold problem or an odor problem. We also do phone consultations for people. They’ll send me some photographs or possibly even a sample, and then I will talk to them on the phone about that. So, we’ve helped quite a few people just that way.

Me: I didn’t know you do phone consults! So, when you’re talking to people over the phone for those phone consultations, do you find, or have you found that there are certain questions that you can ask that seem to be the best questions for getting you the answers you need? In other words, what are the BINGO questions that lead you to the underlying problems?

Mechanical Systems and Indoor Air Quality

Jeff May: Well, I often know from the kinds of symptoms people are having where the key places are to look. I’ll have people email me some pictures or reports beforehand, so that gives me a much better idea of the property and what might be going wrong. For example, I did a study of homes. I compared 600 sick houses that I had investigated to 300 control houses that I had looked at as part of just home inspections. All of these houses were in the Boston area—I found that 19% of the houses that I looked at for home inspections had central air conditioning. And Boston has older housing, so air conditioning at the time was not that common. Thirty eight percent of the houses where people were experiencing health symptoms had central air conditioning. So, from my study, I found that people are twice as likely to have asthma, allergy, respiratory problems if they have central air conditioning.

Me: With all the problems with central heating and air, what do you think is the best way to heat and cool a home in order to avoid the inherent mold problems that come with a centralized system?

Jeff May: I have a lot of allergies–mold allergies and dust mites and pets. I’m also chemically sensitive. So, when we moved from an old house where I experienced some symptoms to a new house that we had built, we decided on forced hot water heat. I think 95% of new houses are built with hot air heat and central air conditioning, because that’s what people want. We had to fight to get forced hot water heat, and we still had to put in air conditioning, because we couldn’t sell this house without it. I didn’t want air conditioning, because unless you live in a relatively arid part of the country, when you cool air in an air conditioning system, there’s water condensation in the system. And so, if there’s any dust at all on a coil or in the vicinity of the coil and the condensation pan, there’s going to be microbial growth in the dust, because it gets wet. And it really only takes just a few days for anything to start growing. The tragedy of most new housing is that when they’re building the house, they’re using the heating system to heat and to cool, so the ducts and coils get covered with sawdust, which is cellulose, and it’s biodegradable. Before people even move in, the system is completely contaminated. Most people aren’t really bothered by it. They might even get a lot of drywall dust blowing out of the system. It’s annoying, but they’re not really bothered by the microbial growth and drywall dust. But then, those that are bothered, get sick.

Me: So how do you prevent that from happening?

Mold Prevention in HVAC Systems

Jeff May: The mechanical system should never be operated during construction. Now, that’s going to be a big problem for a lot of people. But we’ve had clients who are very mold-sensitive. When they were having their houses built, if it was in the wintertime, they had trailer-mounted furnaces parked in the driveway in order to avoid using the duct system. If construction was happening in the summer, they would use portable air conditioners to cool things. If you do that, there would never be any dust in the system. When we had our air conditioning system put in– they didn’t actually put in the cooling units until just before we closed. And every time they installed a duct, they sealed the end of the duct. So, I have the cleanest air conditioning system that I have ever seen. There’s no dust. And it still bothers me when it is on, because of some minute amount of microbial growth hidden somewhere in the system.

Me: Let’s say somebody is– their house is already built and they’re just trying to do as much preventative maintenance as they can. What do you recommend when somebody is doing a renovation? To seal and cover all supplies and intakes and turn off the system during the work and be crazy about cleaning up the dust while it’s happening?

Jeff May: That’s correct. They have to really contain the work area. And if there’s a duct system, it has to be sealed off from the work area. For people who are very sensitive, they should do cleanup on a daily basis as well. A lot of times, when there’s work going on, workers just leave a huge mess, and then start over the next day. So, it certainly minimizes the chances of cross-contamination by daily clean up. And cleanup should always be done with a HEPA-filtered vacuum.

Me: Yes. I totally agree. I find that dust management is hugely helpful for me in terms of my sensitivities. Really getting serious about making vacuuming routine and thorough, helps me to not get sick as often.

Dust Management—the Key to Mold Prevention

Jeff May: Dust is the devil. That’s what I tell people. It’s funny because often they’ll test people for allergies, and there’s something non-specific. They say, “Oh, you’re allergic to dust.” Well, what does that mean? Having looked at 40,000 samples of dust–I take air samples and dust samples, and then I look at them with a microscope and see what’s in the dust. As an example, it’s somewhat unpleasant, but if you look at just typical house dust that settles, let’s say, in a week or two on a surface, it’s mostly just skin scales and cellulose fibers from paper, lint in clothing, and that sort of thing. The dust is relatively benign at that point (assuming it doesn’t contain pollen or pet-dander particles, to which some people are allergic). But actually, dust is food. 90% of dust is skin, human skin. And those skin scales are protein, which is food for microarthropods, which are little bugs that crawl around and that you don’t see. So, when you don’t dust, there is more food for these bugs. For example, if you go into a closet that you haven’t cleaned in 10 years and take everything out from the floor and look at the baseboards, and you’ll see that instead of gray settled dust, there’ll sometimes be orange dust or little spots, colored spots. This happens to books on shelves too. Initially, the dust is nice and gray and sort of homogeneous. But, if you look at it 10 years later, there are all of these kinds of spots. Those spots are all the droppings from all the microarthropods that have been eating all the dust. So, there’s book lice and dust mites and spiders and silverfish, all these different things foraging around. And spiders are the ultimate consumers. They only eat live insects. If you see a lot of spiders in an indoor environment, that means that there’s a miniature, even invisible food chain present, because the spiders may be eating things that you can’t see. All microarthropod fecal material is allergenic. The most common microarthropods that people are familiar with are dust mites. That’s what’s in beds and couches and pillows. If a house has a mold-growth problem, a mite problem will usually be present. People are usually only familiar with house dust mites. But in fact, there are other species of mites that eat mold, and mites that eat mites. And all mite droppings are allergenic. Then, as the mites go around, disturbing the dust and depositing fecal matter, they are also providing food for other organisms. Book lice are also microarthropods. Under my microscope I sometimes see big fecal pellets full of chewed up pollen grains from book lice. There’s this sort of invisible war going on, with spiders at the top of this tiny food chain. Even spider droppings can be allergenic. So, going back to the original question, you want to get rid of dust, because you don’t want to be feeding the soldiers in the war.

Spider Droppings on Wood Floor

Me: People just have to get real about cleaning.

Hidden Sources of Indoor Mold

Jeff May: Yup. That’s right. Keeping things dry and clean is just really, really critical. It’s a never-ending battle. When I inspect a home, I go into every room in the house and check every single piece of furniture with a mirror and a flashlight. A lot of times, people will have antiques in the home. And they’re beautiful and clean, but the bottom is full of mold. I have found hundreds and hundreds of pieces of furniture in bedrooms, and in dining rooms and kitchens, where people are sitting on moldy chairs or eating at tables full of mold at the bottom. Very often, people will buy antiques that have been stored in somebody’s garage. With antiques, often you don’t know where something’s come from. The top may look beautiful, but the bottom and the back can be all covered with mold. One piece of furniture can be a very big source of mold in the environment. If people want to check furniture for mold growth, they can go around with a flashlight and a mirror and look at the bottom and the back of everything in the house. You just can’t believe the things that you find.

Mildew on underside of basement piano seat

Me: What a great tip! I don’t even know who taught me this, but this was a great little tip too. Just about when I got my latest HEPA vacuum, it actually has a light on it. So, I like when I’m vacuuming to shine that light underneath furniture to see the layer of dust that you can’t normally see.

Mold on underside of chair

Tricks for Finding Hidden Sources of Mold Growth

Jeff May: The trick to seeing dust and mold is to hold a bright flashlight at a glancing angle so that the particles will scatter light. We go into rooms and shine the light on a piece of furniture, and there’s mold all over the thing because it was stored in somebody’s basement. People don’t detect a musty odor so they don’t know the mold is there. I mean, you may not smell anything, and mold may have been there for years, but the allergens persist, even if the mold is dead.

Me: So, we know you’ve got your flashlight and your mirror when you go into homes. What other tools do you take with you for inspections?

Jeff May: My nose is always with me, and my lungs. I’ve been doing IAQ inspections for so long that I can sense things quickly. I’ll be in one room and there’s no problem, and go in the hallway and just step into the next room at the door and start to react to something. I do have many instruments that I bring with me, though. Obviously, the moisture meters to test the moisture, and a camera. I have different kinds of air sampling devices too. The most useful thing to me is an air sampler, which is a small machine that holds a glass slide with grease on it. The machine sucks air in, and particles in the air stick to the grease on the slide. Then I stain the slide and look at it with a microscope. When I first started doing this work, I would just take an air sample and look at it. Then I realized that you really have to disturb the dust a little bit to get a reasonable sample of what is in the home. And just as an example, I looked at a crawl space one time during a real estate deal. Supposedly, it had been remediated, but all the fiberglass insulation was still there at the ceiling between the joists. The crawl space itself was perfectly clean and had a concrete floor. I put the air sampler in there and took an air sample for six minutes, and there were no mold spores in the sample. Then, I waved my notebook three times, and there were 16,000 Aspergillus spores per cubic meter of air.

Me: Oh, man!

Jeff May: If you don’t disturb the dust, you come up with very meaningless values, unless there are other sources of IAQ problems, like moldy air conditioning or heating that’s blowing air around. But for people who are involved in legal situations about mold, I will make sure to wave a notebook around and walk on a carpet before I take a sample. Many times, a property management company hires somebody to do the testing, and the tester walks in, and doesn’t disturb any surfaces. Then the person takes an air sample, and there’s no mold in the air at all. What that sample doesn’t reflect are the 1,000’s of mold spores that are settled. So how you sample is critical if you’re trying to find the problem. When I am on a job, there are two things that I want to do: I want to know whether the client has exposure to something, and if so, what and where is the source? In order to find the source, you have to take samples. I also take what I call “pat” samples, which is something that I invented. I go up to a piece of furniture, a cushion, or a carpet, and I hit it gently with a spatula to disturb the dust the way someone would walking on a rug or sitting on a chair, and then I take an air sample. That gives me an idea of what is in that cushion or rug. I’ve found all kinds of serious exposure issues from sampling this way. If you know that there’s something in the air that’s making people sick, you have to identify the particle, and then you have to ask, well, what’s the source of that particle and where might that source be?

Air Testing the Right Way, Lab Reports, and the Benefits of an Inspector Who Knows How to Use a Microscope

Me: So, you do recommend air testing? I guess what I’m saying is, when it’s done right, you recommend it. Correct?

Jeff May: I can’t tell you how many lab reports I’ve looked at that are just completely wrong or the data has been misinterpreted. The most common mold spores outdoors are basidiospores from mushrooms. I read a report from a fellow who was told to demolish his bathroom because there were basidiospores in the air in the bathroom. To demolish and rebuild his bathroom would have cost him about $30,000. But the basidiospores were from outdoors. The crucial thing for air sampling is that you have to identify if there are chains of spores. The most important species of mold indoors in terms of exposures that can impact health are Penicillium, Aspergillus, and Cladosporium. Now, Stachybotrys, that so-called black toxic mold, can make people sick, but you rarely see the spores in the air because the spores are heavier than Penicillium, Aspergillus and Cladosporium spores, so they settle onto surface more quickly. If Aspergillus, Penicillium, or Cladosporium molds are growing indoors, the spores appear in chains or clusters. If those same spores are outdoors, because of the air turbulence, they don’t really appear in chains or clusters. So, if you see one chain of Aspergillus or Penicillium spores indoors, there’s a mold problem. Period. It doesn’t matter what the count is, because a chain of those spores cannot be there unless that mold is growing on something indoors. There’s only one lab that I know of that reports on whether or not the spores occur in chains or clusters (Q Lab in NJ, although EMSL will do so upon request). There are probably over a hundred labs that analyze the data from air samples, but they are missing the most important point: the appearance of the spores. By looking at my own samples, I often know where the mold growth may be located because of the appearance of the spores. For example, Cladosporium is a type of mold that often grows in air conditioning systems. When it is in the air conditioning system and there’s a lot of airflow, the spores actually get dirty and have little black particles (soot or carbon) on them. So, when you look in the microscope and you see a cluster of dirty Cladosporium spores, even if there’s only five of them, it doesn’t matter. There’s mold growing in the system somewhere. Period. And again, none of the labs really report on that. They’ll give you an outdoor count of Cladosporium spores and an indoor count of Cladosporium spores, and the indoor count is a tenth of the outdoor count, and so the lab tells you, “This is a normal indoor count.” But there’s mold growing in the air conditioning system.

Me: That is so common. Mold growth in air conditioning systems is often missed completely. It was in our home. Speaking of missed or hidden mold problems, how often are you taking cavity samples?

Common Areas of Hidden Mold Growth

Jeff May: I’ve been in some places, say a home with an intense musty odor, and found no mold spores. In one property I found a little crack in the exterior brick under a second-floor bedroom window. Water was overflowing off the roof and getting into that crack. Then, the water went down the wall cavity from the second-floor bedroom to the entrance way and into the basement. There was no exterior visible sign of mold anywhere in the house. But the smell of the mold was so unbelievably strong at the front entry. So, a musty smell is a big indicator. The odor of mold growth consists of molecules called microbial volatile organic compounds (MVOCs). And those molecules are much smaller than the spaces between the gypsum crystals in the drywall. That’s why the smell just comes right through the drywall. But the actual spores from the growth cannot get through the drywall at all because they’re way, way too big. So, you can have very significant exposure to the odor and have no exposure to the spores at all.

Me: What about other common, but hidden mold exposures?

Jeff May: Well, in older homes, many times there is wainscoting on the walls. For example, we had a Victorian house built in 1894. My office had wainscoting – you know these vertical wooden boards around the lower third of the wall? There were some gaps between the boards. On certain days, I had trouble breathing in my office. I couldn’t figure out why. One day, I realized my breathing trouble seemed to occur when the wind was blowing outdoors from the northeast at the wall. So, I took an air sample at the crack between the two boards. I found Aspergillus spores coming in through the crack that were covered with coal soot. The mold in the dust in those wall cavities had been there for years and was coming into my office. I put a little bit of removable tape over a couple of the cracks and solved the problem. The point here is that if you have an older home, you probably don’t have insulation in the wall cavities. So, when the wind blows on the wall, it can actually pressurize the wall cavity and blow spores or whatever else is inside those cavities into your home. I’ve even found mold-eating mite fecal pellets blowing in through an electrical outlet. But, if all the walls are insulated, there’s much, much less air movement and it’s much less likely for anything to be coming into the home from a wall cavity. That is also why I don’t like to make holes in wall cavities to test them. Instead, I use a plastic box with a hole in it, and put my air sampler over that and bang the wall to take an air sample. The banging disturbs any mold that might be on the back of the drywall or in the wall cavity, and then it pulls spores out via the electrical outlet, because all outlets have holes and are leaky. So, I can test wall cavities where there are electric boxes, switches, or outlets that way. And many times, I find numerous mold spores.

Me: You have the mind of the detective! That is so cool! You are definitely the exception and not the norm, though. Many mold inspectors are very myopic and don’t really dig deeper or investigate to find the problem. It is just some indoor and outdoor mold samples, and then they are gone.

Jeff May: We’re constantly going back into places that have been remediated or inspected, and we still find all kinds of problems. I’ll tell you another hidden source of problems — refrigerator drip pans. Again, I discovered this the hard way. I was sitting in my kitchen, and every once in a while, I’d start to wheeze, but just couldn’t understand why. One day, I realized every time the refrigerator turned on, I would have trouble breathing. Our refrigerator was only three years old, but in those days, the drip pan was accessible from the front. When I removed the grille and took it out, there was a pearl onion that somehow bounced into it. The onion had an inch and a half of Penicillium mold growing on it. So, every time the compressor turned on, it would blow mold spores out into the room. Every frost-free refrigerator has a heating cycle. The cooling coil gets full of ice, and you have to melt that ice in order for the refrigerator to cool. The water from that melt goes into a pan at the bottom. The heat from the compressor is supposed to evaporate the water, but very often, the water persists. There’s just not enough heat. So, if there’s any dust in that pan, mold growth ensues. And if you’re allergic to cats and dogs, and somebody had a pet in the house before you moved in, that refrigerator can be a perpetual source of allergens just from the dust that accumulated on the coils when the pets were there. We’ve had people who have just simply cleaned their refrigerator, and all of their allergies went away.

Bioslime (bacteria and mold) from drip pan on refrigerator coils

Refrigerator coils with mold spores, dust, and pet dander.

The other big one is baseboard convectors and radiators. Whenever there’s airflow, you get dust accumulating. The air comes in at the bottom, and goes out at the top. Whatever dust there is gets trapped in the middle between the heating elements and can get very moldy, because when the water in the heating system is cool, the temperature around the unit is hot and humid, condensation forms in the dust. Then, mold grows. A lot of allergens get trapped there too. You have to clean radiators and baseboard heating convectors. You can HEPA vacuum the radiators to get the dust off, but with the baseboard convector, there’s a metal plate at the front. If you take that off, you can vacuum that, but you can’t get the dust out from between the fins. You can clean those with steam from a steam vapor machine—it’s basically like a kettle on wheels and puts out high-pressure steam. You put some rags underneath the fin tubing and you blast the fins with steam, and it just about sterilizes those surfaces. Even units that look clean, when you blast the fins, the rags all turn black. So, I would say that, for anybody with any kind of allergies at all, running a fan to move air and also operating exhaust and supply fans in windows to vent the dust should be the first thing you do before moving yourself and even any of your belongings into a home, even one that’s newly constructed.

Moldy dust on fin tubing in baseboard convector heater

Proper Duct and HVAC Cleaning

Me: What about if someone wants to clean their ducts and central HVAC system properly? How should they do that?

Jeff May: The EPA doesn’t really promote duct cleaning. Part of the problem is that when the EPA did its original study, they hired blow-and-go companies. Such companies just have a truck-mounted vacuum out in the street, and then they just suck the dust out of the ducts. You have to send brushes through the ducts to clean them. Also, if a home has air conditioning or even a furnace, the most important part of the cleaning, or at least equally important, is that the blower cabinet and the air conditioning coil be cleaned. I would say that more than half of the furnaces that I open up have exposed fibrous insulating material inside and the blower cabinet is at the bottom of the furnace. Dust accumulates in the insulation. Since the mechanical systems are usually placed in basements, the floor is cold and sometimes damp, and then you get mold growing in the insulation. A lot of the companies, if they even clean the insulation will just vacuum it. Vacuuming doesn’t really get rid of the mold at all, because it’s trapped in the fibers. So, the insulating material has to be very carefully removed, and not even necessarily replaced, because it’s primarily for soundproofing. But if it’s to be replaced, it’s better to replace it with closed cell foam. Then the blowers have to be cleaned. For the air conditioning, you have to clean the coil. Actually, physically clean the coil, get all the dust and mold off. And then, if there’s fibrous insulation around the coil, that has to be cleaned too or replaced. But, in many, many cases, you cannot even access the cooling coil. It’s completely housed in sheet metal with no way to get to it, to clean it, or even inspect it. I’ve devised a little test where I’ll put an air sampler on top of a floor register and then turn the system on. Then, I’ll bang the walls around the air conditioning coil. I’m nervous about doing this test, because if there’s mold, you’ll see many, many spores come pouring out of that system. I want to minimize the exposure as much as possible, so I’ll open windows to air the house out. But if the coil is inaccessible, there’s really no other way to find out if there’s mold growing there except by doing that, unless you drill a hole into the system. If there is mold growth, I will see the spores in my air sample.

Air Filtration and Purification

Me: In terms of filtration and your mechanical systems, do you recommend certain kinds of filters or whole-home air purification systems? Is there anything in terms of preventative maintenance or for allergy sufferers that you recommend?

Jeff May: For any heating and air conditioning system, you have to have good filtration. The best filtration that you can use is a pleated media filter. They are sold in all the big-box stores and many hardware stores. They’re one-inch filters, pleated media filters. The ASHRAE, American Society of Heating, Refrigerating and Air-Conditioning Engineers, says you cannot have air conditioning with a filter less than a MERV 8 rating. That’s MERV, M-E-R-V, minimum efficiency reporting value or a rating system for filters. For people with allergies, it’s better to have a MERV 11 filter. A HEPA filter is about a MERV 16, but you can’t really put that on a heating system, because it’s too restrictive of the airflow. The one-inch filters are not that deep, so they do restrict the airflow as they get clogged with dust. The four- or five-inch pleated filters are much better. They’re a lot more expensive, though, and you have to install a special housing for them. An Air Bear is a great filter. It comes pre-assembled. Aprilaire also makes very good filters for their whole-home purification systems, but they have to be assembled. Using that level of filtration on your central system makes an enormous difference. (For me, the most important function of an air filter is to keep the system clean.)

Portable air purifiers can be very helpful, but they’re not really the answer. I always believe in removing the source of the problems first, and then air filters can be very effective in cleaning. If you can position the airflow of a good air filtration machine to blow directly on you, sometimes, it can help minimize exposure. Once I was able to speak in a moldy basement as long as I stood in the airflow from an IQ Air machine that had a goose-neck flexible duct to direct air into my breathing zone. As soon as I stepped out of the airflow, I started to cough. IQ Air has just come up with something called an ATEM, A-T-E-M. It’s a little desktop unit that’s designed to blow HEPA-filtered air in your face. So, I always recommend something like that if you’re in a workplace where you can’t breathe, and if you’re more or less at a desk. With an ATEM, you can actually have an air filter that directs HEPA-filtered air towards your face. And that can make a difference between having a workspace livable and not livable. The important thing is that you have that purified air stream going directly at your face. Otherwise, you will still have that exposure.

DNA-Based Mold Testing–Is It Necessary? Valuable?

Me: Well, Jeff. This has been amazing. So much valuable information. But, before we close our conversation today, I do want to ask you one last question about testing. What are your thoughts on DNA-based mold testing, like the ERMI or EMMA Tests? Do you do those during inspections? Do you find value in that type of testing? Many doctors advise patients to do it, but it is so expensive.

Jeff May: DNA testing is useful, and very helpful for scientific studies, like with the excellent paper you discussed on your blog about the distribution of mold spores in homes. I don’t think those scientists could have done it any other way. As a matter of fact, the EPA says it’s a research tool. But I’ve been to so many places where people only use ERMI (Environmental Relative Moldiness Index) testing. In some real estate deals, buyers had big ERMI results and they didn’t want to buy the house, but there was nothing actually wrong. In other places, they had low ERMI results and there were mold problems present. The tests were originally developed for carpets only. So, if you don’t do the test by vacuuming your carpet, like two square meters each in the living room and the bedroom, you can’t use that ERMI scale to determine your results or exposure to get an accurate picture. If you test the tops of shelves and other surfaces, you can’t compare the numbers to that ERMI scale, because that ERMI scale was developed for carpets. ERMI results can therefore be confusing. If you want to know the species of fungi present (and only the 36 species used in the test), though, ERMI rest results can be useful.

Me: My issue with just doing an ERMI is that, at the end of the day, you want to help people solve the problem. And just knowing your ERMI score doesn’t always tell you if the mold problem was historic or is still an issue. It also doesn’t help you to locate or fix the problem.

Jeff May: Exactly. In one test where I did indoor and outdoor ERMI cloth wipes, the Aureobasidium pullulans count was very high indoors, but it was also very high outdoors. If I had only done the ERMI test indoors, I would not have known about the outdoor source for the mold. Yet someone could have had just one moldy leaf on their shoe and walked into the house from the exterior. ERMI tests have helped some people to find hidden mold, but the test is costly. In my opinion, the most important thing is to have a really thorough visual inspection done and to have the IAQ inspector take some air and dust samples to see where the problems are. With that information, you can make better decisions.

Me: Well, thank you for taking all of this time. I hope that more and more doctors and indoor air quality professionals can work together to help people. The environmental piece of healing, in my opinion, really is the most important. If you can get that right, you can really help someone make a full recovery. It certainly worked for me and my family.

Jeff May: Happy to speak with you. Thank you for interviewing me.

Comments? Questions? Write to me below or at catherine@moldfreeliving.com. For more information on Jeff May, his business and his books, please visit his website www.mayindoorair.com and www.myhouseiskillingme.com. All four of his books are available on Amazon. Edition two of “My House is Killing Me” is scheduled to be published in the fall of 2020. Jeff also offers phone consulting; 978-649-1055. The fee is $85 per half hour, including time to review any reports or photos sent in advance.

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Monica - 2:24 am

Love this! Great interview. So informative and I’m actually blown away by the sheer amount of knowledge May has on mold and his unparalleled creativity for testing for it. Inspiring to say the least. Mold sick mama of two, we’ve moved four times in the last year due to mold exposure after spending two years in an (invisible to the naked eye) toxic Chateomium nightmare. Love that you are sharing the truth and knowledge for all. How did you find a mold free home after your exposure?

Catherine - 7:50 pm

Hi, Monica,
We actually left and stayed with family and in hotels for about 4 months while we fully remediated our home. We basically had to take it down the studs, and replaced our HVAC system, ductwork, and removed and replaced all insulation in our attic. It was a tremendous overhaul, but was the only way to make the home safe for us to be there. It still took about a year of me continuing to clean for mold and HEPA vacuum, etc. for the home to “feel” right for me again. I can safely say that we are all doing quite well and are continuing to recover and thrive now.

Thank you for reading and for writing to me!


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