There are a a variety of indications you need house ventilation, including:
1. Enduring odors
If you have issues getting powerful smells out of your house, you could have a ventilation issue.
2. Musty air
The air in your space should be fresh, but stale zones mean you could have inadequate ventilation.
3. Disproportionate dust
Dust can develop more frequently in areas with insufficient ventilation.