There is a significant lack of indoor air quality research in low energy homes. This study compared the indoor air quality (IAQ) of eight new-build case study homes constructed to similar levels of air-tightness and insulation, with two different ventilation strategies (four homes with MVHR/Code level 4; four homes with natural ventilation/Code level 3). IAQ measurements were conducted over a 24 hour period in the living room and main bedroom of each home during the summer season. Simultaneous outside measurements and an occupant diary were also employed during the measurement period. Occupant interviews were conducted to gain information on perceived IAQ, occupant behaviour and building related illnesses. Knowledge of the MVHR system including ventilation related behaviour was also studied. The results suggest IAQ problems in both the mechanically ventilated and naturally ventilated homes. Lower humidities were recorded in the Code 4 homes, possibly due to use of MVHR.