November 3, 2016

This blog was originally posted on ProTradeCraft and has been lightly edited.

Poor IAQ is such a serious issue that the Environmental Protection Agency (EPA) lists it as a top five environmental threat and asthma is one of the most serious chronic illnesses among American children, according to the Centers for Disease Control and Prevention (CDC). Because the increase in Indoor Air Quality (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 national matter, 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 CAUSE great IAQ because they eliminate accidental sources of bad air, like musty crawl spaces, radon-ridden basements, exhaust-filled garages and dusty attics.

Sources of indoor pollution

Contaminants may come from outside the home, or from within the home. 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. 

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.

As heat, moisture, and UV act on building materials, the materials break down into contaminants in the form of gasses and particles. For each 20 degrees) F rise in temperature, a building material can double its off-gassing rate.

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.

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 an efficient mechanical ventilation system.

If you have a forced air heating and cooling system, you can use a supply ventilation fan to distribute fresh outside air throughout the house..  

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 path of the pollutant by 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.

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.

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