Most of the modern air-conditioned buildings have a low fresh air supply to reduce energy consumption. This results in a poor indoor air quality (IAQ) and a 30–200% higher sick building syndrome than that of a naturally ventilated building. Alternatively, energy-efficient and eco-friendly earth air tunnel system (EATS) provides a good IAQ because of the sufficient fresh air supply. This paper presents the cooling performance and IAQ characteristics of a sparsely occupied building supported with an EATS. The building was monitored for the concentration of fine and coarse particulate matter (PM), carbon dioxide (CO2) and carbon monoxide (CO), temperature distribution and relative humidity (RH) in September and October 2012. The average PM10, PM2.5 and PM1 concentrations were 6.77, 6.11 and 3.17 μg/m3 respectively when the EATS was operated. These are marginally higher compared to that when the EATS was not operated. The average indoor CO2 level, air temperature and RH were 418 ppm, 26.5 °C and 58.2% respectively when the EATS was operated. The diurnal indoor CO2 trend relates well with photosynthetic and anthropogenic activities in and around the building. The CO2 and PM concentrations correlate well with indoor air temperature and RH with a time lag. © 2017, Metrology Society of India.