Ventilation and Indoor Air Quality
Why ventilate
Homes are tighter than they used to be, so pollutants and moisture build up without deliberate ventilation. Candidates should know the main pollutant classes: moisture, combustion byproducts (CO, NO2), volatile organic compounds, particulates, radon, and biological contaminants. Know that source control comes first, then local exhaust, then whole-house ventilation.
Local and whole-house strategies
Local exhaust includes kitchen hoods (vented outdoors, sized to the range) and bath fans (typically 50-110 cfm, run long enough to clear moisture, often 20-30 minutes after a shower). Whole-house strategies include exhaust-only, supply-only, balanced (HRV/ERV), and intermittent or continuous operation. Know that an HRV transfers sensible heat, an ERV transfers both heat and moisture, and that ERVs are often chosen in humid climates. Traps: bath fans vented into the attic or soffit, recirculating range hoods counted as exhaust, and unbalanced ventilation that creates pressure problems.
Combustion safety and backdrafting
Understand that exhaust fans can depressurize a house and backdraft naturally drafting appliances. Know the role of the CAZ (combustion appliance zone) test, spillage, and the need for makeup air where required.
Worked example
A 2,000 square-foot home uses ASHRAE 62.2-style continuous ventilation. A common simplified rule is about 7.5 cfm per occupant plus 0.01 cfm per square foot, with occupants = bedrooms + 1. For 3 bedrooms and 2,000 sq ft: 4 occupants x 7.5 = 30 cfm, plus 20 cfm = 50 cfm continuous. Confirm the exact formula your exam references before applying it.