There are a a variety of signs you should look into house ventilation, such as:
1. Ever-present odors
If you have issues getting strong smells out of your home, you could have a ventilation issue.
2. Musty air
The air in your space should be fresh, but musty zones mean you likely have issues with ventilation.
3. Lots of dust
Dust can develop more often in rooms with stifled airflow.