Ventilation and Air Quality in New California Homes with Gas Appliances and Mechanical Ventilation

Conditioning air that enters California homes through building and ductwork leaks uses a substantial amount energy, typically about a third of all energy used for heating and cooling, so making energy use more efficient by sealing leaks is essential to achieving zero energy homes in California. At the same time, outdoor air contributes to healthy indoor air quality by diluting pollutants emitted inside the building. To ensure acceptable indoor air quality, California’s Title 24 Building Standards require ventilation in new homes built since 2008. This report presents a comprehensive study of the effects of these requirements in recently built homes with natural gas appliances. The study included a survey on occupant satisfaction with air quality and ventilation-related activities like using range hood that affect air quality; a field study of homes built in 2008 or later; and simulations on how various ventilation rates might affect exposures to indoor pollutants as homes become more “air tight” in California.
The field study included 70 homes built between 2011 and 2017. The researchers monitored each home over roughly one week with the mechanical ventilation system operating and windows closed. The study found that the bulk of homes met most ventilation requirements and that ventilation fans on average moved 50 percent more air than the minimum specified in Title 24. Air pollutant concentrations were similar or lower than those reported in a study of recently constructed California homes done in 2007-08 before the minimum ventilation requirement. Measured concentrations were below health guidelines for most pollutants, indicating that indoor air quality is acceptable in new California homes when mechanical ventilation is used. However, labeling and controls for ventilation systems need to be improved.
Based on project findings, the researchers recommend that the core ventilation requirements of dwelling unit and local exhaust ventilation should remain in the Title 24 Building Energy Efficiency Standards for the foreseeable future.