A hybrid ventilation system controlled by a pressure difference sensor was installed on a detached test house. Performance of this ventilation system was evaluated through the field measurement taken into account the different conditions of the air supply and the exhaust systems. The results of the measurement revealed that the exhaust airflow rate was relatively stable while the indoor-outdoor temperature difference varied and the wind velocity changed. The exhaust airflow rate met the target airflow rate of 64% during the whole measuring period. From the comparison about the air supply systems, the crawl space air supply system showed better result than the passive air supply system not only for the balance of air supply in the first floor and the second floor but also for the stability against various outdoor condition.