In 2008 the State of California adopted new building codes that required the use of mechanical ventilation systems in homes that meet the requirements of ASHRAE Standard 62.2. The standard requires both a dwelling unit mechanical ventilation system and exhaust fans in kitchens and bathrooms. A field study was undertaken to evaluate the IAQ and ventilation performance of homes built to these requirements. For ventilation system performance, the airflows of all mechanical ventilation systems were measured and their use was monitored for a one-week period. To evaluate IAQ, key pollutants were measured indoors and outdoors during the week, and occupants completed satisfaction surveys. The key pollutants included: formaldehyde, humidity, PM2.5 and NO2. Passive samplers were used to determine average concentrations for the week. Active samplers were used to develop time-series results that can be used to correlate pollutant concentrations with occupant activities. Other ventilation/IAQ related parameters were also recorded, such as stove top temperatures to indicate cooking, exterior door contact switches to know when large openings were being used for ventilation and sensors to determine when clothes dryers were being used. The building envelope and duct leakage were measured to enable estimates of infiltration and duct leakage effects. This paper presents an overview of the test procedures and preliminary results from several homes. The results show that although average concentrations may be reasonable compared to available standards (with the exception of formaldehyde), occupants have a strong impact on pollutant variability and source strength and that outdoor concentrations cannot be ignored. Overall, these mechanically ventilated homes have reasonable IAQ. The homes and duct systems are moderately tight, though not excessively so, by US standards. Significant concerns have been expressed regarding compliance with the ventilation requirements in the California building code. However, almost all the ventilation systems in this study complied with the ventilation air flow requirements and on average were significantly higher than the minimum required air flow rates.