Air Quality
Air Quality
The Air Quality domain tests ventilation, filtration, and source control. NATE expects you to apply ASHRAE 62.2-style whole-house ventilation, select filters by MERV and pressure drop, and verify combustion safety.
Core rules
- Whole-house ventilation rate for a home: Q = 0.01 × floor area + 7.5 × (bedrooms + 1). Local exhaust: bathroom fan 50 cfm intermittent or 20 cfm continuous; kitchen 100 cfm intermittent or 25 cfm continuous.
- MERV 8–13 captures most particulates; higher MERV increases pressure drop and can reduce airflow unless the fan is rated for it.
- Keep the house pressure-balanced. A tight house needs makeup air for large exhaust fans; backdrafting a natural-draft water heater is a carbon monoxide hazard.
- Measure CO in ambient air and in flue gas after the appliance has reached steady state. Ambient CO should stay below 9 ppm; flue CO air-free should be compared with the appliance manufacturer’s limit.
Worked example
A 2,000 ft² house with three bedrooms: Q = 0.01 × 2,000 + 7.5 × (3 + 1) = 20 + 30 = 50 cfm continuous. A 50-cfm bath fan run intermittently does not satisfy the whole-house requirement, and a 100-cfm kitchen fan can depressurize the house unless makeup air is provided.
Traps
Assuming the highest MERV is always best; using a bathroom fan as the only ventilation; measuring CO before steady state; and ignoring return-air pathways that starve the air handler.