Indoor Environmental Quality: Sources, Ventilation, and Measurement
Categories of indoor pollutants
Indoor environmental quality covers biological, chemical, particulate, and combustion pollutants. Candidates should know representative sources: moisture and dust mites, mold, and pests for biological; volatile organic compounds from finishes, adhesives, and furnishings for chemical; cooking, candles, and outdoor infiltration for particulates; and gas ranges, fireplaces, and attached garages for combustion byproducts including carbon monoxide and nitrogen dioxide. A reliable exam trap is attributing a symptom or odor to the wrong category, or assuming that a new home is low-risk when new materials often off-gas.
Ventilation strategies
Distinguish source control, dilution ventilation, and filtration. Source control is preferred: vent the dryer outdoors, seal the garage interface, use a range hood that exhausts outside. Dilution ventilation includes local exhaust (bath and kitchen fans) and whole-house strategies such as balanced systems with heat or energy recovery. Filtration captures particles but does not remove gases or moisture. Questions frequently test whether a recirculating range hood or a bathroom fan vented into the attic counts as ventilation; neither removes pollutants from the building.
Measurement and interpretation
Evaluators use humidity meters, moisture meters, carbon monoxide alarms, and sometimes particle or CO2 monitors. CO2 is a rough proxy for ventilation adequacy, not a direct measure of contaminant risk. Trap: treating a single spot reading as conclusive. Take repeated readings, compare indoors and outdoors, and record conditions such as weather and occupancy.
Worked rule of thumb
Bath fans should run long enough to clear moisture; a common guideline is to continue operation roughly 20 to 30 minutes after showering ends, or until mirror and wall surfaces are dry. For kitchens, run the exhaust hood during cooking and for several minutes after. If a fan is noisy, undersized, or ducted into an attic, treat it as nonfunctional ventilation and document it.