Houses are places where people spend most of their time. Consequently, if there is an infected person in the household, the risk of infection increases. To prevent the spread of infection among family members, the importance of having treatment rooms within houses—designed to prevent infectious particles from spreading to other areas—is growing. This paper examines a ventilation system that can be installed in such treatment rooms. In 2022, an experiment was conducted using house treatment rooms as the downstream spaces for a supply ventilation system. However, due to external weather conditions and internal disturbances, it was found that this system was unsuitable for house treatment rooms. Therefore, in 2023 and 2024, the ventilation system was changed to an exhaust ventilation system, and further experiments were conducted. In the exhaust ventilation system, the house treatment rooms are maintained at a higher pressure than other spaces, causing air to flow out. To address this, an auxiliary fan was installed in the treatment rooms, and the experiment was conducted with negative pressure relative to the other spaces. The results of the experiment showed that it is feasible to create treatment rooms in a house using an exhaust ventilation system. Operating the auxiliary fan will help ensure air quality in the treatment rooms and prevent the spread of infectious fluids. The airflow rate of the auxiliary fan was set to approximately 20 m3/h, taking into account the number of occupants and the overall airflow balance in the house.