Ventilation and Indoor Air Quality
What this domain covers
The Ventilation and Indoor Air Quality domain tests whole-house ventilation rates, local exhaust, filtration, pressure balance, and moisture control. In Hawaii's humid marine climate, latent control and mold prevention matter as much as pollutant removal, so the exam expects you to calculate ventilation and recognize when a system is fighting humidity.
Core rules
- Whole-house rate. ASHRAE 62.2 (2016 and later) uses Q = 0.03A + 7.5(Nbr + 1), where A is conditioned floor area in ft² and Nbr is the number of bedrooms. The result is a continuous fan rate in cfm.
- Local exhaust. Bathrooms need 50 cfm intermittent or 20 cfm continuous; kitchens need 100 cfm intermittent or 25 cfm continuous. Local exhaust does not replace the whole-house rate.
- Balanced vs. exhaust-only. Balanced systems (ERV/HRV) avoid depressurization. An ERV transfers moisture as well as heat; an HRV transfers heat only.
- Filtration. MERV rating must be matched to blower capacity and pressure drop. A high-MERV filter on a restrictive return can cut airflow and freeze a coil.
- Source control first. Remove the pollutant, then dilute with ventilation, then filter.
Worked example
A 2,000 ft² conditioned house has three bedrooms. Q = 0.03 × 2,000 + 7.5 × (3 + 1) = 60 + 30 = 90 cfm continuous. A 90-cfm bath fan running continuously can meet the whole-house rate, but if it runs intermittently on a timer, verify delivered cfm with a flow hood. A box labeled 90 cfm that measures 70 cfm at the grille is not meeting the requirement.
Traps that cost marks
- Using the number of occupants instead of bedrooms and forgetting the +1.
- Including garage, lanai, or unconditioned area in A.
- Assuming a range hood satisfies the whole-house ventilation rate.
- Ignoring makeup air; exhaust-only systems depressurize and pull humid outdoor air into the envelope.
- Setting the humidistat too high; keep indoor relative humidity below roughly 60% to limit mold growth.