There are a a couple signals you should look into house ventilation, such as:
1. Lasting odors
If you have problems getting strong smells out of your home, you could have a ventilation issue.
2. Musty air
The air in your home should seem fresh, but musty zones mean you may have issues with ventilation.
3. Disproportionate dust
Dust can build up more rapidly in areas with inadequate air movement.