Researchers estimate that people spend up to 90% of their time indoors. Homes need some means to bring in fresh air and remove stale air on a regular basis to keep the indoor air healthy, especially in today’s more airtight homes. Most state codes use ASHRAE 62.2 as their residential ventilation standard. There are different methods for meeting this standard including supply-only ventilation, exhaust-only ventilation, and balanced air ventilation.