Indoor Air Quality, Filtration, and Ventilation
Indoor Air Quality, Filtration, and Ventilation tests how filtration, outdoor-air ventilation, exhaust, and humidity control interact with air distribution. Expect MERV selection, filter pressure drop, ASHRAE 62.2 ventilation rates, ERV/HRV application, and combustion-safety diagnostics.
Filtration
MERV rates particle capture from 1 to 20; higher MERV usually means higher initial pressure drop and better fine-particle capture. A filter must fit its frame without bypass; gasket or seal the edges. Pressure drop rises as the filter loads, so check the blower's airflow margin before moving to a high-MERV filter. Install filters with the airflow arrow correct.
Ventilation and IAQ
ASHRAE 62.2 sets whole-house ventilation and local exhaust targets. A common whole-house rate is Q = 0.03 × floor area (ft²) + 7.5 × (bedrooms + 1), in cfm; local code may differ. Exhaust-only ventilation can depressurize a house and cause backdrafting of atmospheric combustion appliances. Balanced ventilation with an HRV or ERV limits that risk and recovers heat or moisture. Test CO, humidity, and pressure; do not use CO2 alone as a proxy for all contaminants.
Worked example
A 2,000 ft² house has three bedrooms. Q = 0.03 × 2,000 + 7.5 × (3 + 1) = 60 + 30 = 90 cfm continuous. If the selected ERV delivers 90 cfm and is balanced, it meets the calculated target; verify with a flow hood and check that bath fans and dryer exhaust do not create excessive depressurization.
Traps
Do not assume a higher-MERV filter is always better without checking static pressure and airflow. Do not ignore filter bypass. Do not treat an exhaust fan as makeup air. Do not accept a ventilation rate without verifying actual delivered cfm and house pressure.