New Home Ventilation Solutions



Indoor air quality (IAQ) is more than just a green building buzzword. Poor IAQ is such a serious issue that the Environmental Protection Agency lists it as a top five environmental threat.

Asthma is one of the most serious chronic illnesses among American children, according to the Centers for Disease Control and Prevention. Because the increase in IAQ problems seems inextricably linked to building tighter and tighter houses, the answer may seem simple: stop building tight houses.

Unfortunately, it is not that simple. As energy costs escalate and energy conservation becomes a matter of national security, energy codes respond and specify tighter, more energy efficient houses. Fortunately, tight houses and superior IAQ can go hand in hand when the two are considered together. In fact, tight houses can actually lead to CAUSE great IAQ because they eliminate accidental sources of bad air, like musty crawl spaces, radon-ridden basements, exhaust-filled garages, and dusty attics.

A quick definition of indoor air quality

Before going into detail about IAQ problems and solutions, let’s look at what IAQ is. Because all people are different, there is no set standard for indoor air quality — it is based on tolerance to pollutants. Some people are very chemically sensitive, others are very tolerant. This is why definitions of things like IAQ and comfort must be vague. From our article on IAQ: "As technically defined by the US Environmental Protection Agency (EPA), a home with appropriate indoor air quality maintains indoor air which a majority of occupants find acceptable in respect to both odor and sensory irritation. Indoor air quality is measured through aspects like temperature, humidity, ventilation, and chemical or biological contaminants."

Sources of indoor pollution

Contaminants may come from outside the home, or from within the home’s interior. Common indoor pollutants include mold, bacteria, viruses, allergens, volatile organic compounds (VOCs), radon, carbon monoxide, asbestos, lead, pesticides, respirable particles, and second-hand smoke. All of these pollutants can cause short-term and long-term health effects.

Ways to manage indoor pollution

Dr. Joseph Lsiburek, one of North America's leading building science engineers talks about controlling indoor air pollution in terms of the four P's — people, pollutant, path, pressure. “You can have people in one room and pollution in another, but if a path does not connect them, and there is no pressure pushing the pollution to the people, there really is not a problem.” So in order to solve IAQ problems, we must eliminate one of the four P's. Eliminating the people is the least likely option in a house, so that leaves eliminating the pollutant, the path, or the pressure pushing the pollutant down the path to the people.

Pollutants can come from a lot of places

Dr. Max Sherman, a physicist at the Lawrence Berkeley National Lab, and former chair of the ASHRAE 62.2 committee, describes some common sources of indoor pollution as things that come from cans and bottles (like gasoline, paint strippers, cleaning supplies, and — ironically — 'air fresheners'), building materials, biologicals (mold, dust mites, etc.), and smoke.

Lstiburek describes many indoor pollutants that come from building materials as happening "when things that get really hot, really wet, or exposed to ultraviolet light," and he calls these three items 'damage functions.'

As heat, moisture, and UV act on building materials, the materials break down into contaminants in the form of gasses and particles. Lstiburek says that for each twenty-degree F rise in temperature, a building material can double its off-gassing rate. Similarly, an eighteen percent increase in relative humidity doubles the off gassing in many building materials. Not only can houses in hot and humid climates experience more mold growth, they can experience more off gassing than houses in cold and dry climates.

Eliminating sources of VOCs is the simplest way to avoid indoor pollution

Use low VOC building materials that will not off gas, store toxic chemicals like paint thinner and gasoline in a garden shed outside the house, and exhaust the rooms where pollutants and moisture are produced. "But even after you’ve isolated, eliminated, and exhausted, there are still pollutant sources that are most practically diluted with controlled whole-house ventilation" writes Sherman, who describes three ways to clean the air with fans: "blow out old air (exhaust), suck in new air (supply), or both (balanced ventilation)."

Pull the pollutants out of the living space

The easiest, least expensive, and least invasive way to remove contaminants from a house is to suck them out with continuously running exhaust fans. If you have a forced air heating and cooling system, you can use a supply ventilation fan to distribute fresh outside air through the house. But you still need exhaust fans in the wet rooms. Pairing supply and exhaust fans is technically a balanced system, but the best path to clean indoor air is to use a balanced ventilation fan such as an energy recovery ventilator (ERV) or heat recovery ventilator (HRV) that combines supply and exhaust within one fan unit. HRVs capture heat from the outgoing exhaust air and transfer it to the incoming supply air to save energy and improve comfort. ERVs do the same with the added feature of capturing moisture from overly humid outdoor air.

Controlling the paths means sealing the house tight

As mentioned earlier, a tight house is an excellent way to ensure clean indoor air because sources of pollution are sealed out of the living space. By keeping the indoors in and the outdoors out, it is possible to control where the air you breathe comes from and goes to. Moisture, mold, radon, soil gasses, auto exhaust—even dead animals can contaminate air inside a house if the crawl spaces, basements, garages, and attics are not sealed from the outside. That bonus room over the garage? Potentially a dangerous place for kids to play if not sealed tight and ventilated right.

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