Filtration, Dehumidification & Ventilation
By Emily Mottram
More people than ever are working from home but, unfortunately, most of us don’t have homes that were designed and constructed with the kind of high-quality air systems that many offices have. And though we know how important clean air is to our health, the place that most of us usually think of as safe—our home—too often has poor indoor air quality. To find out how we can address this issue, I asked four experts for insight on what’s going on in our homes and what we can do to make them healthier.
We all know that we can’t survive without air, but most of us would be surprised to learn just how much we breathe. Kristof Irwin, Principal at Austin, Texas-based Positive Energy, says, “We breathe 30 to 40 pounds of air every day. And where does it go when you breathe deeply? Into your blood. We breathe more than we drink, more than we eat, so it has a big impact on our health.”
So, how do we start to improve our indoor air quality? After gathering detailed information from her clients, Portland-based Ripcord Engineering CEO Sonia Barrantes and her team provide an initial analysis of the house and make recommendations, including the pros and cons of the proposed systems, from heating and ventilation to cooking, and what those choices mean from health and energy perspectives. And she doesn’t mince words. “I tell them, ‘If you’re going to do a gas range, we’re going to give you direct exhaust; there’s no room to maneuver on that. You will do it because it’s unhealthy not to.’”
But what happens when you don’t have a mechanical engineer like Barrantes who can tell you exactly what you need to buy and how best to install it? Unfortunately, as Dr. Allison Bailes, founder of Energy Vanguard, notes, most HVAC systems are designed by installers, who may or may not be able to provide the best solution for the client’s needs.
Irwin supports this view: “When an installer or contractor says, ‘What I recommend is…,’ the rest of that sentence is based on what the contractor knows, what they don’t know, what their local distributor sells, what they think they can service afterwards, what they can make a profit on, or what you’re not going to call them back for because there is an issue.”
There are many reasons for this and, certainly, some installers do a fine job at designing and installing systems. But, as the homeowner, you need to know a little bit about what is available and what it does, so you can make the right choices for your home and your health.
Dehumidification: why you need it and how to get it
A moist cake is wonderful. A moist house, not so much. Excess moisture in a house will damage the structure—and our health. But how do you know if you need a dehumidifier? Irwin says that one easy way is to look outside: “If you have lush grass in the summer, with dew on it in the mornings, chances are very good you need a dehumidifier.”
Of course, this depends on the individual situation. Nikki Krueger, Building Science & Business Development Manager at Therma-Stor, warns, “When we [cite] these ranges for safe indoor humidity levels of 40%–60%, we’ve got to be careful. Because if I had tried to get to 40% indoor humidity in the winter in Wisconsin, my windows would have been covered in condensation.”
Barrantes concurs. “As mechanical engineers, we’re really uptight about people actively humidifying, because we’re afraid that they’re going to get condensation, and it’s going to drip down and create mold and other issues. So we try to actively discourage our clients from adding humidification.”
But we just told you that you probably need to dehumidify your home, right? So why do we need to do this in a place with such long winters? Because summers in Maine are getting more and more humid, and even though the outdoor temperatures aren’t always high, people feel uncomfortably warm and think that the way to fix things is to install air conditioners and turn their thermostats way down. Yet they don’t realize that what they really need to do is address the indoor humidity. So they wind up with cold, clammy houses, when they really needed to control the indoor humidity first, then the temperature. The same is true in our shoulder seasons. The temperature outside isn’t high, but the humidity is rising because the cooler air can’t hold as much moisture.
It’s not enough to take only the outdoor humidity into account; when you’re dealing with humidity in your house, you need to first look underneath it. If you’ve got a crawl space or basement, half of the air in those spaces is going to end up in your living space. And even if you don’t have a basement or crawl space, excess moisture in the indoor air also comes from cooking, showering, breathing and construction materials, to name just a few of the most common culprits.
That feeling of discomfort you get in a humid home is annoying, but there are far worse byproducts of interior moisture: mold, mildew and rot. As humidity increases, the building itself gets wetter and wetter, but you just don’t see it—at least not at first, and sometimes not at all. Will things smell musty and moldy to you when you have a problem? Not necessarily. Will you see something when you have a problem? Again, not necessarily. But there is a simple solution: put the appropriate-sized dehumidifier into your home, and it can keep the air dry.
So what do you buy? Krueger says that most people’s first instinct may be to get a portable unit but typically the ones from big box stores come with short warranties and the homeowners find themselves replacing them repeatedly, until they realize that the best solution in the long run is to invest in a whole-house system that draws air from more than one location, directly empties the water into a drain or to the outdoors and is possibly ducted throughout the entire house, not just the basement.
Filtering the air we breathe
Once you have nice, dry air inside your home, you need to filter it. All of it. If you have a whole-house ERV (energy or enthalpy recovery ventilator) system, though, the filter just needs to remove the outdoor particles. Barrantes feels that Maine homeowners only need a MERV 8 level filter* in their ERVs, which is simply to protect the core from things like dust. “There’s no point in higher filtration here in Maine because the outside air is fresh. And the air being replaced is leaving; it’s not recirculating back into the home.”
Indoor air, however, needs to be filtered. For this you need a better quality filter, like MERV 13. Rarely will a home need high-efficiency particulate air (HEPA) filters. “One of the biggest issues [homeowners need to] understand is that if a ventilation system isn’t sized for better quality filters, you’re going to end up with problems, because the better filters are more resistive,” Bailes says. “Contractors often are the ones doing the design, [but] they’re not the ones who should be doing the design in most cases. There are some good contractors who know what they’re doing and can design systems well. But so many designs use standard one-inch MERV 2 filters. And later on, some homeowner is going to… buy the oneinch MERV 13 filter and put it in the system and cause problems.”
But what if you don’t have a ducted heating system or an ERV? Can you filter the air in your home with a portable air cleaner? The answer is yes. You can even make one yourself. Bailes recently wrote an article about how to make your own portable air cleaners that uses a box fan to create a cost-effective, DIY, four-filter system. “You can spend thousands of dollars on portable air cleaners, and you can get some questionable products that have ionizers and ozone generators; you don’t want those,” she cautions. “Filtration and ventilation are the two best things for indoor air quality. So, focus on those.”
Bringing the outdoors in: ventilate, ventilate, ventilate
An indoor filtration system does the vital job of trapping particles, from dust to pollen to viruses (if you have a really good system). But it doesn’t reduce carbon dioxide, volatile organic compounds (VOCs) or other indoor contaminants. Now we come to the third leg of the three-legged stool of healthy indoor air quality strategy: ventilation. And having a drafty home is NOT true ventilation. That air comes into your home through a crawl space, attic or holes in the envelope. If you haven’t been in your attic recently, pop a head up there and see if the air trapped between your roof and insulation seems like fresh air to you. The same is true for many basements.
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) gives ventilation guidelines that Irwin says are “a reasonable place to start.” Every home needs a system that ensures you’re breathing clean air that came from outdoors.
In Maine, Barrantes says, the outside air is just too dry in the wintertime to use a heat recovery ventilator (HRV). Exhaust-only ventilation systems (bathroom exhaust fan + a make-up air vent) and HRVs often leave you and the other people in the household with cracking skin or, worse, frequent nosebleeds. ERVs, which allow for heat and moisture transfer, are the way to go, and any system you install should have professional verification that it is operating as designed, providing, at minimum, the level of ventilation specified by ASHRAE 62.2, and the owners should be instructed on how to use it properly.
How do you know if you need to ventilate? A good indoor air quality monitor, like a uHoo, Foobot, or Awair, can tell you if the air inside your home needs dilution of any contaminants it might have. But a caveat is in order: Bailes says that monitors are more reliable at showing changes in the indoor air quality than they are in giving absolute numbers, so you need to pay attention to the fluctuations you may see. Monitoring aside, he recommends putting in “the capacity to ventilate for more than what ASHRAE 62.2 requires, and then [give] the homeowner some control over the system, which is one of the things that the standard actually does require. But a lot of times that’s just an on/off switch, and we don’t want homeowners just to turn it all the way off.”
During construction and in brand-new homes, it’s even more important to be vigilant about ventilation to help get rid of excess moisture and the VOCs found in so many building materials.
The most important steps that we can take to create homes that are safe, healthy and comfortable havens are to seek out the best professionals we can find to help us to dry, filter, ventilate and monitor the air we each breathe indoors. All 30–40 daily pounds of it.
This article appeared in the Spring 2021 edition of Green & Healthy Maine HOMES. Subscribe today!
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