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Building Science

How to Manage Indoor Air Quality

Source control, ventilation, dehumidification, and filtration are key to regulating air pollutants such as formaldehyde in our homes

Image courtesy of Aprilaire

Maintaining good indoor air quality (IAQ) requires us to manage a wide range of contaminants. The list runs well into the hundreds and includes radon, mold spores, volatile organic compounds (VOCs), carbon dioxide, and by-products of fossil fuel combustion. To keep these pollutants at acceptable levels we rely on four fundamental strategies: source control, ventilation, dehumidification, and filtration. Together, these form a versatile tool kit that can address most IAQ problems. I plan to explore these strategies in depth in future posts; for now, I’ll introduce each and discuss the role they can play in the management of formaldehyde, a VOC of particular concern.

Source control

Source control needs to be the starting point for every IAQ effort. The fewer pollutants that enter the living space, the less mechanical energy is required to remove them. Source control measures include physical barriers (e.g., crawlspace liners to exclude radon and soil moisture), material choices (low-VOC cabinetry and finishes), and equipment selection (electric induction rather than natural gas cookstoves). It may involve controlling house pressures to avoid drawing in contaminated air from spaces like garages. Occupant behavior and household product choices are also important for source control.


Mechanical ventilation, the second piece of a comprehensive strategy, involves diluting indoor air with outdoor air to reduce pollutant levels. One of the most common ventilation strategies is “exhaust-only”—a bath fan is set to run continuously or on a schedule, and outdoor air enters the house passively through gaps and cracks. More sophisticated systems—including heat recovery ventilators (HRVs), energy recovery ventilators (ERVs), and ventilating dehumidifiers—provide better control of the incoming air; they also allow it to be treated (filtered, tempered, and dehumidified) before it enters the living space. With these systems, the house remains at a neutral or slightly positive pressure, allowing better…

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