There are a a couple indications you need house ventilation, including:
1. Persistent odors
If you have issues getting potent smells out of your space, you could have a ventilation issue.
2. Musty air
The air in your house should be fresh, but stuffy spots mean you might have inferior ventilation.
3. Disproportionate dust
Dust can build up more quickly in areas with inadequate airflow.